View Full Version : Reliability Improvements M16 - M4A1
List the reliability improvements that have been implemented starting with the military fielding the M16 through the M4A1. (Not civilian AR's)
For organization list the improvements that only pertain to reliability in the cycle of operation and those that addressed known issues and increased service life. Not furniture, sights, etc.
For example chrome lining barrels, what corrective actions were taken to address bolt failures, extraction issues, etc.
Hopefully we can put it in chronological order later.
Buffer weight was changed to slow the cyclic rate due to a switch from IMR powder to ball powder....I think.
Copper extractor spring and black insert.
The forward assist was added, but that will probably incur some denial as to it's addition to reliability.
magazines, springs, and followers went through multiple iterations.
standard 5.56 round went through a few revisions as well. I suspect a gunpowder changed quite a bit to improve performance/reliability.
thicker barrel on M4A1 (socom) probably didn't improve reliability as much as stability under high rate of fire.
magazines, springs, and followers went through multiple iterations.
standard 5.56 round went through a few revisions as well. I suspect a gunpowder changed quite a bit to improve performance/reliability.
thicker barrel on M4A1 (socom) probably didn't improve reliability as much as stability under high rate of fire.
The early gun powder change actually made the rifle less reliable by jacking up the cyclic rate from about 750 rpm to something like 950 rpm. If I remember correctly, this powder fouled more.
Within the parameters of reliability in the cycle of operation it doesn't appear there was much to improve upon the original Stoner design with the gun itself.
Midlength gas system on the URGI.
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Wasn't there a problem with bolts breaking after the GWOT kicked off?
Seems like that was do to a manufacturing process that didn't require any design modifications...
Chrome lining of bore/chamber, fencing on lower receiver, forward assist, thickened barrel profile (A2, M4, SOCOM), extractor insert, O ring and gold extractor spring, M4 feed ramps, various buffer weight corresponding to barrel length and gas port size.
Wasn’t the extractor spring upgrade a result of the change in barrel length and gas system from rifle to carbine?
Within the parameters of reliability in the cycle of operation it doesn't appear there was much to improve upon the original Stoner design with the gun itself.
Agreed. In fact, skimping on Chrome lining was the decision of MacNamara if I remember correctly. And that's the only TRUE reliability improvement I've read in this thread. The other stuff is nice, but not a reliability improvement.
I also recall an issue with bolts breaking prematurely and Colt actually discovered a flaw in the manufacturing process? So the bolt design was unchanged.
Agreed. In fact, skimping on Chrome lining was the decision of MacNamara if I remember correctly. And that's the only TRUE reliability improvement I've read in this thread. The other stuff is nice, but not a reliability improvement.
This is like saying 1911 is better than Browning Hi-Power. When clearly Browning himself didn't think that was the case since he started working on Hi-Power.
There are a number of issues with the original design. Reliability issues were/are due to both materials and design. Fairly minor ones have been addresses with the official incremental changes listed above (not just chrome lining).
Others issues are inherent to the design and as a result you see significant design changes of HK416 and AR18, and to a lesser degree KAC SR-15 and LMT.
COLT has also made a number of subsequent variants and design improvements, unfortunately non of them were released to the public. I don't remember the exact model numbers, but somebody can chime in with more knowledge on Colt variants including piston and re-designed lower.
This is like saying 1911 is better than Browning Hi-Power.
I don't follow the logic. We're not comparing different weapons.
There are a number of issues with the original design.
I would imagine there were issues with the original design, like any new weapon system. But the military fielded M16 really suffered from the jungle environment and lack of chrome in the bore combined with the mis-info on maintenance for the soldiers/marines.
I can't remember ANY other improvements related to reliability. And none of the other points brought up in this thread are reliability improvements for the M16 at all.
This video covers some of the changes.
https://youtu.be/NYar4Zf8jH8
I don't follow the logic. We're not comparing different weapons.
I would imagine there were issues with the original design, like any new weapon system. But the military fielded M16 really suffered from the jungle environment and lack of chrome in the bore combined with the mis-info on maintenance for the soldiers/marines.
I can't remember ANY other improvements related to reliability. And none of the other points brought up in this thread are reliability improvements for the M16 at all.
The improved extractor spring increased reliability.
Improved magazines increased reliability.
Changes to the buffer were made to improve reliability.
Shot peening of the bolt was an early enhancement.
Not a reliability improvement, but Colt proposed the following:
"Upper and Lower Receiver. Shot peen the surfaces to provide a more durable finish and to aid in the prevention of exfoliation and inter-granular corrosion."
I don't think the Army ever approved that one (?).
There are quite a number of changes that improved reliability that people don't know about, or over-look.
There were 145 changes made during the first contract, and 68 further changes made during the second contract.
A large number of these were simple house-keeping, changing the drawing to match the parts as manufactured, or accepting parts that were not quite made to print. However, a good number of them were product improvements, albeit minor ones, like adding a drain hole to the ejector spring passage in the bolt to prevent hydro-locking of the ejector, or changing the gas tube from regular steel to stainless steel.
I don't think a single part escaped modification between the first contract and the acceptance of the drawing package license in 1968.
Shot peening was introduced for a number of parts.
A more interesting question is:
"What changes were made to the M16A1 to make the M16A2 that were improvements to the combat usability of the rifle?"
To discuss changes made to the design to accommodate the M4 configuration is immaterial, as the M4 is a different beast altogether.
The early gun powder change actually made the rifle less reliable by jacking up the cyclic rate from about 750 rpm to something like 950 rpm. If I remember correctly, this powder fouled more.
The early lots of Ball Powder not only increased the cyclic rate but it had too much calcium carbonate added I believe to kill flash which led to increased fouling and as the gas tube fouled it raised pressure which caused the rate to go even higher.
But there are two types of early reliability improvements that need to be considered, the mechanical of which being fielded in a tropical environment the chrome lined bore and chamber was one of the most important. Then you have the other little changes that improved not the mechanical reliability but the combat reliability like fencing off the magazine release, closing off the flash suppressor and fielding cleaning kits and supplies.
The early lots of Ball Powder not only increased the cyclic rate but it had too much calcium carbonate added I believe to kill flash which led to increased fouling and as the gas tube fouled it raised pressure which caused the rate to go even higher.
But there are two types of early reliability improvements that need to be considered, the mechanical of which being fielded in a tropical environment the chrome lined bore and chamber was one of the most important. Then you have the other little changes that improved not the mechanical reliability but the combat reliability like fencing off the magazine release, closing off the flash suppressor and fielding cleaning kits and supplies.
AMMUNITION:
There seems to be a lot of confusion about the propellant used, and why. It should be remembered that the primary propellant used in all 5.56mm still is a ball propellant. And up until M855A1, it was basically the same propellant.
1) The original specified propellant was IMR 4475, which wasn't the best choice, as a few years earlier the Army had tried it in 7.62mm and rejected it as giving to wide a pressure variation (Investigation of Ballistic and Chemical Stability of 7.62mm Ammunition Loaded with Ball and IMR Propellant, June 1962). Also, the energy density of the IMR propellant was a little shy of where it needed to be to achieve the required 3,300 fps and stay below 52,000 psi. IMR 4475 could not meet the requirements, full stop. In fact, it was so well known that IMR 4475 would not meet requirements, no ammunition manufacturer tendered a bid on the first full scale production solicitation.
The only available propellants that could meet the ballistic and pressure requirements were Winchester's ball powders. So, it was either use ball propellant or not have a round*. The choice of WC 846 was logical, as it was used with good reliability in 7.62mm of all types.
2) Calcium carbonate (CaCO3) is used in the production of ball propellants to neutralize the acids and stabilize the resulting mixture. You have to ensure that enough is added to neutralize all the acid, so normally there will be some left over. This excess CaCO3 will be deposited in the gun after the propellant burns so ball propellant is considered somewhat "dirty". SOME lots of 5.56mm had very high levels of excess CaCO3 and it can clog the gas tube causing failure to function. Testing showed that propellant with CaCO3 levels at the high end of the tolerance band could be problematic. CaCO3 is also very good at preventing throat erosion so it is not desirable to eliminate it altogether, in fact, 7.62mm for machine guns has additional CaCO3 in it and is designated "WC 846+CaCO3". The corrective action was simply to make two types of WC 846, WC 846 for 7.62mm ad WC 846 for 5.56mm, each with the correct CaCO3 level for best operation. WC 846 for 5.56mm was later re-designated as WC 844., and was the primary propellant for M193 and M855 for forty years without further issues.
3) The original "Edgewood" buffer was not a very good buffer. It was very light and used a series of steel cones and split rings to achieve a spring effect. The problem is once dirt, moisture and/or corrosion get into the the system the split rings and washers lock together and it ceases to be a spring. This results a higher than normal rate of fire and in very bad bolt bounce with associated failure-to-fire in full automatic. The slower burning WC 846 did increase the rate of fire to around 900 rpm with the "Edgewood" buffer, but the new buffer designed to correct the bolt bounce was heavier and also corrected the high rate of fire issue.
It should be noted that for unrelated issues, tracer ammunition continued to be loaded with IMR propellants (IMR 8208M), and showed poor reliability when loaded 100% tracer after the introduction of the new buffer. The bolt velocity was too low, they were under gassed. But, since tracer is usually loaded 4 ball to 1 tracer, you could usually burp through a weak IMR round. Later, WC 844 was approved for tracer.
The problems with the change from IMR 4475 to WC 846 were not unforeseen, as Winchester, Springfield Armory and Frankford Arsenal suggested testing to ensure compatibility in the rifle-ammunition combination before a wholesale switch. However, the representatives from the Office of the Secretary of Defense (OSD) rejected testing as an "unnecessary expense" and "might delay procurement".
CHROMIUM PLATING:
The lack of chromium plating for the bore was not a oversight, but a technical limitation. We take chrome plating a bore for granted these days, but in 1963-64, things were different. Achieving a uniform thickness, well adhered, plating layer on a hole with such a large length-to-diameter ratio was difficult. They were having problems with chrome plating flaking in the .30" M14 and M60 bores around this time. In 1957, almost immediately after seeing the AR-15 Springfield Armory began to investigate how to plate .22 caliber bores to the exacting requirements of a gun barrel (Chromium Plating of Caliber .22 Barrel Bores, June 1957). They knew how important it was to have a chromium plated chamber and bore.
_ _ _ _ _ _ _ _
* Another option was redesign the bullet, but that was rejected, as "unnecessary".
AMMUNITION:
There seems to be a lot of confusion about the propellant used, and why. It should be remembered that the primary propellant used in all 5.56mm still is a ball propellant. And up until M855A1, it was basically the same propellant.
1) The original specified propellant was IMR 4475, which wasn't the best choice, as a few years earlier the Army had tried it in 7.62mm and rejected it as giving to wide a pressure variation (Investigation of Ballistic and Chemical Stability of 7.62mm Ammunition Loaded with Ball and IMR Propellant, June 1962). Also, the energy density of the IMR propellant was a little shy of where it needed to be to achieve the required 3,300 fps and stay below 52,000 psi. IMR 4475 could not meet the requirements, full stop. In fact, it was so well known that IMR 4475 would not meet requirements, no ammunition manufacturer tendered a bid on the first full scale production solicitation.
The only available propellants that could meet the ballistic and pressure requirements were Winchester's ball powders. So, it was either use ball propellant or not have a round*. The choice of WC 846 was logical, as it was used with good reliability in 7.62mm of all types.
2) Calcium carbonate (CaCO3) is used in the production of ball propellants to neutralize the acids and stabilize the resulting mixture. You have to ensure that enough is added to neutralize all the acid, so normally there will be some left over. This excess CaCO3 will be deposited in the gun after the propellant burns so ball propellant is considered somewhat "dirty". SOME lots of 5.56mm had very high levels of excess CaCO3 and it can clog the gas tube causing failure to function. Testing showed that propellant with CaCO3 levels at the high end of the tolerance band could be problematic. CaCO3 is also very good at preventing throat erosion so it is not desirable to eliminate it altogether, in fact, 7.62mm for machine guns has additional CaCO3 in it and is designated "WC 846+CaCO3". The corrective action was simply to make two types of WC 846, WC 846 for 7.62mm ad WC 846 for 5.56mm, each with the correct CaCO3 level for best operation. WC 846 for 5.56mm was later re-designated as WC 844., and was the primary propellant for M193 and M855 for forty years without further issues.
3) The original "Edgewood" buffer was not a very good buffer. It was very light and used a series of steel cones and split rings to achieve a spring effect. The problem is once dirt, moisture and/or corrosion get into the the system the split rings and washers lock together and it ceases to be a spring. This results a higher than normal rate of fire and in very bad bolt bounce with associated failure-to-fire in full automatic. The slower burning WC 846 did increase the rate of fire to around 900 rpm with the "Edgewood" buffer, but the new buffer designed to correct the bolt bounce was heavier and also corrected the high rate of fire issue.
It should be noted that for unrelated issues, tracer ammunition continued to be loaded with IMR propellants (IMR 8208M), and showed poor reliability when loaded 100% tracer after the introduction of the new buffer. The bolt velocity was too low, they were under gassed. But, since tracer is usually loaded 4 ball to 1 tracer, you could usually burp through a weak IMR round. Later, WC 844 was approved for tracer.
The problems with the change from IMR 4475 to WC 846 were not unforeseen, as Winchester, Springfield Armory and Frankford Arsenal suggested testing to ensure compatibility in the rifle-ammunition combination before a wholesale switch. However, the representatives from the Office of the Secretary of Defense (OSD) rejected testing as an "unnecessary expense" and "might delay procurement".
CHROMIUM PLATING:
The lack of chromium plating for the bore was not a oversight, but a technical limitation. We take chrome plating a bore for granted these days, but in 1963-64, things were different. Achieving a uniform thickness, well adhered, plating layer on a hole with such a large length-to-diameter ratio was difficult. They were having problems with chrome plating flaking in the .30" M14 and M60 bores around this time. In 1957, almost immediately after seeing the AR-15 Springfield Armory began to investigate how to plate .22 caliber bores to the exacting requirements of a gun barrel (Chromium Plating of Caliber .22 Barrel Bores, June 1957). They knew how important it was to have a chromium plated chamber and bore.
_ _ _ _ _ _ _ _
* Another option was redesign the bullet, but that was rejected, as "unnecessary".
Was there any changes made to the manufacturing process of the bolt or to the bolt itself other than upgrading the extractor spring and insert/buffer?
MikhailBarracuda91
02-06-22, 07:16
Was there any changes made to the manufacturing process of the bolt or to the bolt itself other than upgrading the extractor spring and insert/buffer?This is a great point to bring up. I graduate from machinist apprentice school in June, and then go on to train under a journeyman.
Manufacturing processes as a whole have gotten much better, even since the 90s. We use GD&T (geometric dimensioning and tolerencing) even though they used GD&T to measure back in the 60's they didn't have computers or CNC machines like we do now
It's really amazing if you compare modern manufacturing to even 50 years ago. It's so much easier to hold tolerance to the blueprint, and faster to make parts with less mistakes
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Was there any changes made to the manufacturing process of the bolt or to the bolt itself other than upgrading the extractor spring and insert/buffer?
8 Apr 64 - Modified drain hole for ejector spring passage.
14 May 64 - Extractor, extractor spring and ejector spring, changes to improve reliability.
6 Aug 64 - Ejector spring, minor changes
8 Oct 64 - Ejector spring, minor changes
10 Nov 64 - Extractor, change in spring seat hole
20 Jan 64 - Bolt, revised requirements for staking cam pin hole
7 May 64 - Bolt, extractor, ejector, and extractor pin, change to Parkerized finish
27 May 65 - Bolt, change in hardness requirement
6 Jan 66 - Bolt, shot peen cam pin hole area, scatter peen remaining areas
1 Feb 66 - Bolt and extractor minor dimensional changes to extractor hole location and tolerances
16 Dec 66 - Ejector and extractor pin shot peen
27 Oct 67 - Bolt, changes to improve tolerancing
Other high points:
Nov 64 - Stainless steel gas tube
Dec 66 - first rifles with new buffer received by Army
May 67 - Hard chrome plating on firing pins
Changes that were proposed in the 1960's but not approved (foreshadowing):
Handguard slip rings with angled outer diameter (as done on the XM177E2), to permit easier disassembly
Round, interchangeable handguards
Nested extractor spring (the extractor spring with the rubber insert wasn't approved until 1971)
Add windage marks on rear sight
Wasn't there a problem with bolts breaking after the GWOT kicked off?
Seems like that was do to a manufacturing process that didn't require any design modifications...
I thought this was a quality control issue with Colt at the time that has since gotten resolved?
MikhailBarracuda91
02-06-22, 08:33
I thought this was a quality control issue with Colt at the time that has since gotten resolved?It sounds like a heat treat issue.
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MikhailBarracuda91
02-06-22, 08:48
I would say CAD/CAM and high speed machining could be an improvement.
You guys might think I'm not following the format but hear me out
The TDP for any firearm is just a blueprint. You can create a 3 dimensional object in a CAD program like fusion 360, bobcad, etc. Even enter values like mass, velocity, surface finish, you name it. And make the gun function via a simulation.
The CAD drawing (object) is dimensionally perfect. Now you can write the entire G code to machine it by hand like they used to (still useful sometimes) but CAM software uses post processing to do it for you, and with high speed machining.
The job will be so precise (if you have the right machine and tools) I'm talking within 99.9% accuracy for everything. From gun to gun
That's literally impossible to do on a manual setup like they did back in the day. This is why the AR-15 is so much more reliable nowadays.
The AK would also benefit from modern technologies, but it was always very reliable from the beginning.
I can only imagine where we'll be in 20 years
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8 Apr 64 - Modified drain hole for ejector spring passage.
14 May 64 - Extractor, extractor spring and ejector spring, changes to improve reliability.
6 Aug 64 - Ejector spring, minor changes
8 Oct 64 - Ejector spring, minor changes
10 Nov 64 - Extractor, change in spring seat hole
20 Jan 64 - Bolt, revised requirements for staking cam pin hole
7 May 64 - Bolt, extractor, ejector, and extractor pin, change to Parkerized finish
27 May 65 - Bolt, change in hardness requirement
6 Jan 66 - Bolt, shot peen cam pin hole area, scatter peen remaining areas
1 Feb 66 - Bolt and extractor minor dimensional changes to extractor hole location and tolerances
16 Dec 66 - Ejector and extractor pin shot peen
27 Oct 67 - Bolt, changes to improve tolerancing
Other high points:
Nov 64 - Stainless steel gas tube
Dec 66 - first rifles with new buffer received by Army
May 67 - Hard chrome plating on firing pins
Changes that were proposed in the 1960's but not approved (foreshadowing):
Handguard slip rings with angled outer diameter (as done on the XM177E2), to permit easier disassembly
Round, interchangeable handguards
Nested extractor spring (the extractor spring with the rubber insert wasn't approved until 1971)
Add windage marks on rear sight
Nothing after the 1998-1999 increase in bolt consumption?
How was that resolved?
Dunno if its helpful for the broken bolt discussion, but I saw a few in the early GWOT. Then suddenly, bolts stopped breaking, at least in my experience. I’m pretty sure there’s an AMU or Crane armorer floating around here that can piece that puzzle together.
Nothing after the 1998-1999 increase in bolt consumption?
How was that resolved?
I don't have that hard data on changes later than 1969. But, I do know at some point the area of shot peening was extended to include the locking lugs, and there were a lot of tests with other fatigue reducing processes like low plasticity burnishing and laser peening.
I don't have that hard data on changes later than 1969. But, I do know at some point the area of shot peening was extended to include the locking lugs, and there were a lot of tests with other fatigue reducing processes like low plasticity burnishing and laser peening.
Thank you for the information. I really appreciate it!
The TDP for any firearm is just a blueprint...
Blueprints are only a small part of a TDP. TDP includes how a company will do business with the government. It covers safety, waste disposal, training, manufacturing processes and who knows what all. Companies with government contracts jealously guard their TDP to keep competitors from coming in and under bidding them.
The TDP for any firearm is just a blueprint.
Not hardly . . . .
https://i.imgur.com/923gcHV.jpg
Yes, that is a full sized M14 for scale. 1465 documents, of which only 174 are the actual part drawings.
https://i.imgur.com/qYwcX7O.jpg
Not hardly . . . .
https://i.imgur.com/923gcHV.jpg
Yes, that is a full sized M14 for scale. 1465 documents, of which only 174 are the actual part drawings.
https://i.imgur.com/qYwcX7O.jpg
WOW!!
MikhailBarracuda91
02-07-22, 22:27
Blueprints are only a small part of a TDP. TDP includes how a company will do business with the government. It covers safety, waste disposal, training, manufacturing processes and who knows what all. Companies with government contracts jealously guard their TDP to keep competitors from coming in and under bidding them.That's really incredible to see how specific they are.
So if the M16 had a TDP somewhat similar to this, then they wrote out specific manufacturing processes (which are outdated now) I wonder how much of the TDP is still used. I'm sure the materials, dimensions, and lots of other things.
It seems like nowadays a data package would be a reference point. We've far surpassed any capabilities from back then
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TDPs are changed as needed. If a company comes up with a better way to do things, they can submit a proposal to change or add to the TDP. Or, the government can propose a change. For example, TDPs changed over the years concerning the handling and disposal of chemicals and which chemicals are authorized. TDPs have changed as new safety procedures have been adopted and security tightened. TDPs are never “one and done”.
The one other thing I thought of that could arguably be considered a reliability improvement (designed for the mil) is the A5 buffer system. It's intended use really would only maintain the reliability of the Rifle buffer system. So it's not really an M4 improvement.
TDPs are changed as needed. If a company comes up with a better way to do things, they can submit a proposal to change or add to the TDP. Or, the government can propose a change. For example, TDPs changed over the years concerning the handling and disposal of chemicals and which chemicals are authorized. TDPs have changed as new safety procedures have been adopted and security tightened. TDPs are never “one and done”.
Industry likes the term "a living document" . . .
I have always wondered if they changed the depth of the hole for the front pivot pin spring. The old TM shows to drill a 1/16" hole in the springs channel 1" back from the front edge cut on older lowers if the hole was not there. Using today's depth numbers, location, and tolerances that older 1" number hole could be so far back it would miss the spring channel completely or only partially catch it. Maybe it was just a mistake in the TM when it said to go back that far. Someone told me it was because the old Colt print started the spring channel depth from a different point than what the newer drawings, but I have never had access to see the old Colt drawing.
One manufacturer sold some lowers using the old 1" inch from the cut and newer hole depth. The 1/16" hole only partially accesses the springs channel on the right side of the hole.
MikhailBarracuda91
02-09-22, 23:18
TDPs are changed as needed. If a company comes up with a better way to do things, they can submit a proposal to change or add to the TDP. Or, the government can propose a change. For example, TDPs changed over the years concerning the handling and disposal of chemicals and which chemicals are authorized. TDPs have changed as new safety procedures have been adopted and security tightened. TDPs are never “one and done”.This is why M4C is the best place on the web for AR info. A lot of members here are really knowledgeable.
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titsonritz
02-10-22, 13:35
Dispelling the myth their new rifle were “self-cleaning” and issuing cleaning kits/instructions along with using the correct type of powder in the ammo seemed to do more for AR reliability than anything else.
I have always wondered if they changed the depth of the hole for the front pivot pin spring. The old TM shows to drill a 1/16" hole in the springs channel 1" back from the front edge cut on older lowers if the hole was not there. Using today's depth numbers, location, and tolerances that older 1" number hole could be so far back it would miss the spring channel completely or only partially catch it. Maybe it was just a mistake in the TM when it said to go back that far. Someone told me it was because the old Colt print started the spring channel depth from a different point than what the newer drawings, but I have never had access to see the old Colt drawing.
One manufacturer sold some lowers using the old 1" inch from the cut and newer hole depth. The 1/16" hole only partially accesses the springs channel on the right side of the hole.
That TM is not in error. The center of the hole is at 1 inch from the front face of the boss.
The hole for the detent spring hole for the pivot pin is 1.125 in from the center of the pivot pin hole. The front face of the boss is 0.145 in from the center of the pivot pin hole. That means the spring hole is 0.980 in deep (1.125 - 0.145 = 0.980). The specified cross hole to be drilled is 1/16 inch, or 0.062 inch. That means 0.031 in goes forward of the center and 0.031 in goes behind. That means the forward edge of the newly drilled hole sits at 0.969 in (1.000 - 0.031 = 0.0969). It will intersect the spring hole, as there is an 0.011 in overlap.
The hole could not have been deeper, as the length of the spring and detent determine that dimension and it has to match the takedown detent hole.
You have to ignore the tolerances just to get a partial intersection. Try it with the minimum hole depth and maximum distance back for the face of the boss and tell me how much intersection you get then.
I think measured from the face of the boss the current holes max center may only be about .915". This allows the complete hole to intersect the spring channel. There are a lot of brand lowers that are drilling the full spring depth from the face of the boss instead of the center of the pivot pin. You wind up with a spring flush or below the face of the boss. They must be using a drawing from somewhere that shows it like that for more than one to be doing it.
You have to ignore the tolerances just to get a partial intersection. Try it with the minimum hole depth and maximum distance back for the face of the boss and tell me how much intersection you get then.
I think measured from the face of the boss the current holes max center may only be about .915". This allows the complete hole to intersect the spring channel.
Nope, did not ignore the tolerances.
You did not take into account the length of the hole specified on the drawing is the length of the cylindrical portion of the hole*. In a drilled hole there will always be an 118 degree cone added to the end of the cylindrical portion from the drill point**. In this case with a 0.097" hole the drill point cone adds another 0.029" to the total length.
https://i.imgur.com/cRT6VOe.jpg
There are a lot of brand lowers that are drilling the full spring depth from the face of the boss instead of the center of the pivot pin. You wind up with a spring flush or below the face of the boss. They must be using a drawing from somewhere that shows it like that for more than one to be doing it.
Yes, there are a lot of people making things wrong.
The correct depth of the hole is from the center of the pivot pin hole, full stop.
______________________-
* That is standard practice from ASTM Y14.5 - Dimensioning and Tolerancing.
** Which is shown on the drawing, by the way.
An added angle to a bit just to try and reach the curve edge of a 1/16" hole that does not give the full access to the spring channel as intended. The current hole location that cannot be located that far back by the drawing. The whole point of the hole was to give access to the channel to assist in removal of frozen springs and detents. I doubt it was to give some little piece of a odd shaped attempt at a hole past the normal end of the channel. Either channel hole was deeper or the 1" was someone's mistake which was corrected by moving the hole further forward on the drawing.
The point of the hole is to allow water to drain out of the hole and reduce corrosion of the spring and detent.
The location of the hole for production is different from the manual's retrofit instructions.
Dispelling the myth their new rifle were “self-cleaning” and issuing cleaning kits/instructions along with using the correct type of powder in the ammo seemed to do more for AR reliability than anything else.
I'm in no way disputing this post at all. But it occurs to me that we use stick and ball powder in our ARs and almost never clean most of them. And there's no reliability issues at all... ever. Perhaps the combination of jungle environment is the additional factor that caused problems... with the lack of chrome lining.
I'm in no way disputing this post at all. But it occurs to me that we use stick and ball powder in our ARs and almost never clean most of them. And there's no reliability issues at all... ever. Perhaps the combination of jungle environment is the additional factor that caused problems... with the lack of chrome lining.
There are multiple factors.
- Hot-wet conditions. Most folks shooting and not cleaning are not shooting in wet condition, which makes the carbon fouling gummy.
- Lubricants. Most modern lubricants, even motor oil, have some detergents in them that do make them "self-cleaning" to a minor degree. Back in the 1960s, issue oil, VV-L-820, was basically just a lubricant.
- Training. Even those that do not clean these days know to "keep it wet". Try shooting a few thousand rounds without injecting some oil in it every so often.
- Modern ball propellant, while not the cleanest, is better that some lots of WC 846.
- Soft brass. This is probably the most overlooked problem with early M16 reliability. There was no officially approved case drawing for the 5.56mm until around 1969 or 70. If you look at the graph below, you can see that soft brass (low yield strength) will not spring back sufficiently to release from the chamber, resulting in failure to feed due to low bolt velocity to cases stuck hard in the chamber requiring driving out with a cleaning rod. It also exacerbates the problems associated with pitted chamber.
https://i.imgur.com/SgkSOjl.png?1
This would also be a good time to note that the 1963 manual for the M16, explains the importance of cleaning and lubrication in order to keep thing running properly. It also goes into great detail on how to clean it. The problem is that procurement of the cleaning kits was not put on the same priority as the M16s themselves. Neither the cleaning implements nor the manuals were issued in sufficient numbers. I highly doubt any sergeant in the Army believed that any weapon was "self-cleaning", but without the tools to do it, what are you going to do?
- Soft brass. This is probably the most overlooked problem with early M16 reliability.
That's interesting. I never read/heard about that component of the equation.
I'm in no way disputing this post at all. But it occurs to me that we use stick and ball powder in our ARs and almost never clean most of them. And there's no reliability issues at all... ever. Perhaps the combination of jungle environment is the additional factor that caused problems... with the lack of chrome lining.
I don't know if this is pertinent, I think all medium fast burn rate stick and ball powders we can get off the shelf have the ability to give us the correct pressure curve to run all gas system lengths, carbine, mid, and rifle. I bought some Radway Green surplus, maybe 15 years ago, that would only run in my carbine gas length rifle, would not run a mid or rifle. It seems to me that the commercial market for AR powders is a bit more squared away than the market for military powders. Maybe they just experiment more trying to squeeze the best performance out of a powder, but then, sometimes mess up or just cook up a powder from the get go that was never meant to run in different length gas systems. IDK.
That's interesting. I never read/heard about that component of the equation.
It is mentioned very briefly in the book, "The Black Rifle", but if you read through all of the testimony given in the Ichord Hearings, I think it is Frank Miller, goes into great length about case hardness.
Stoner gave somewhat misleading testimony, in that he alluded that the problems with stuck case was due to the increase in cyclic rate, but that is just flat incorrect, but Stoner was "the inventor", and Miller(?) was just an engineer at APG. So, guess what became the official culprit in the stuck case issue?
I don't know if this is pertinent, I think all medium fast burn rate stick and ball powders we can get off the shelf have the ability to give us the correct pressure curve to run all gas system lengths, carbine, mid, and rifle. I bought some Radway Green surplus, maybe 15 years ago, that would only run in my carbine gas length rifle, would not run a mid or rifle. It seems to me that the commercial market for AR powders is a bit more squared away than the market for military powders. Maybe they just experiment more trying to squeeze the best performance out of a powder, but then, sometimes mess up or just cook up a powder from the get go that was never meant to run in different length gas systems. IDK.
I had some of that stuff too. It would choke a Colt AR 20" rifle. I don't even know how you can make a round that will do that. And it was hot enough (from reading the brass). My best guess was that powder was too fast. But crap... we load fast benchrest powders all the time with no issues.
That TM is not in error. The center of the hole is at 1 inch from the front face of the boss.
The hole for the detent spring hole for the pivot pin is 1.125 in from the center of the pivot pin hole. The front face of the boss is 0.145 in from the center of the pivot pin hole. That means the spring hole is 0.980 in deep (1.125 - 0.145 = 0.980). The specified cross hole to be drilled is 1/16 inch, or 0.062 inch. That means 0.031 in goes forward of the center and 0.031 in goes behind. That means the forward edge of the newly drilled hole sits at 0.969 in (1.000 - 0.031 = 0.0969). It will intersect the spring hole, as there is an 0.011 in overlap.
The hole could not have been deeper, as the length of the spring and detent determine that dimension and it has to match the takedown detent hole.
Please tell me you didn't just pull this from memory.
Impressive posts in this thread, thank you for the time and effort you're going through.
I don't know if this is pertinent, I think all medium fast burn rate stick and ball powders we can get off the shelf have the ability to give us the correct pressure curve to run all gas system lengths, carbine, mid, and rifle. I bought some Radway Green surplus, maybe 15 years ago, that would only run in my carbine gas length rifle, would not run a mid or rifle. It seems to me that the commercial market for AR powders is a bit more squared away than the market for military powders. Maybe they just experiment more trying to squeeze the best performance out of a powder, but then, sometimes mess up or just cook up a powder from the get go that was never meant to run in different length gas systems. IDK.
Given my experiences with reloading for the AR, I have to wonder how the Brits managed to create ammunition that caused functional problems. In its current point of development, the AR platform simply does not seem to be finicky to load for.
I know they did it, it just makes me scratch my head at how.
I am not confusing my experiences with experience, by the way.
Andy
Given my experiences with reloading for the AR, I have to wonder how the Brits managed to create ammunition that caused functional problems.
My exact sentiment. How is it even possible? It wasn't underpowered at all. Rifle system is worst, and I already load really fast powders that fun fine in rifle gas systems. It's like they loaded it with pistol powder that burnt up in the first 10" of barrel.
Given my experiences with reloading for the AR, I have to wonder how the Brits managed to create ammunition that caused functional problems. In its current point of development, the AR platform simply does not seem to be finicky to load for.
I know they did it, it just makes me scratch my head at how.
I am not confusing my experiences with experience, by the way.
Andy
My exact sentiment. How is it even possible? It wasn't underpowered at all. Rifle system is worst, and I already load really fast powders that fun fine in rifle gas systems. It's like they loaded it with pistol powder that burnt up in the first 10" of barrel.
The British were manufacturing ammunition tailored to the L85A1 or A2, not the M16 . . .
I had some of that stuff too. It would choke a Colt AR 20" rifle. I don't even know how you can make a round that will do that. And it was hot enough (from reading the brass). My best guess was that powder was too fast. But crap... we load fast benchrest powders all the time with no issues.
The British were manufacturing ammunition tailored to the L85A1 or A2, not the M16 . . .... and it was shitty.
"TACOM Maintenance Advisory Message 05-038 authorizes the use of British 5.56mm rounds for training only with the M16A2/A4 rifle, the M4/M4A1 Carbine, and the M249 Machinegun. The British round leaves more residue, which causes the weapon to jam if not cleaned frequently."
https://i2.wp.com/rifleshooter.com/wp-content/uploads/2015/01/PM-2.jpg?w=597&ssl=1
The point of the hole is to allow water to drain out of the hole and reduce corrosion of the spring and detent.
The location of the hole for production is different from the manual's retrofit instructions.
The 68 TM states to drill the hole as a repair to a frozen detent so the associated parts can be removed after soaking with a wire. Page 3.2.1.
... and it was shitty.
"TACOM Maintenance Advisory Message 05-038 authorizes the use of British 5.56mm rounds for training only with the M16A2/A4 rifle, the M4/M4A1 Carbine, and the M249 Machinegun. The British round leaves more residue, which causes the weapon to jam if not cleaned frequently."
https://i2.wp.com/rifleshooter.com/wp-content/uploads/2015/01/PM-2.jpg?w=597&ssl=1
I can think of at least 10 off the shelf powders we can get that will operate any of the gas length AR's just fine, but yet the Brits come up with some janky powder that only works in their crappy short stroke piston guns. It probably didn't work that well in their piston guns either, that's why they dumped it on the surplus market.
... and it was shitty.
"TACOM Maintenance Advisory Message 05-038 authorizes the use of British 5.56mm rounds for training only with the M16A2/A4 rifle, the M4/M4A1 Carbine, and the M249 Machinegun. The British round leaves more residue, which causes the weapon to jam if not cleaned frequently."
https://i2.wp.com/rifleshooter.com/wp-content/uploads/2015/01/PM-2.jpg?w=597&ssl=1
The most interesting thing there is the claim that a 249’s effective range is a kilometer with M855 and half that with M193. I’m now curious how that was calculated.
Ability to perforate an M1 helmet was the original metric.
Ability to perforate an M1 helmet was the original metric.
500m with 193 and 1000m with 855, though? Thats a huge difference. I thought 600 was the limit with M855 for the helmet thing?
Edit: just ran some numbers…. We’re looking at ~transonic pistol velocities around 800-ish yards with M855 and around 650-ish yards with M193. No way is M855 going through a steel helmet at 1000 meters. 900fps on a real good day. Real good day, probably not reality. Looks like M193 gets down to 900fps around 880 meters with the same caveat.
Iirc, tracer burnout on the Mk46 was written as 800m in the manual… does it go to 1,000 from a 21”? Whats tracer burnout on the red tip?
Edit 2: I checked the 249 TM… doesn’t list tracer burnout, but does list max effective range on a area target at 1,000m. Better be shooting at a sizeable element to test that.
The changes to the M4 feed ramps. Also the multiple generations of magazine followers.
500m with 193 and 1000m with 855, though? Thats a huge difference. I thought 600 was the limit with M855 for the helmet thing?
Edit: just ran some numbers…. We’re looking at ~transonic pistol velocities around 800-ish yards with M855 and around 650-ish yards with M193. No way is M855 going through a steel helmet at 1000 meters. 900fps on a real good day. Real good day, probably not reality. Looks like M193 gets down to 900fps around 880 meters with the same caveat.
Iirc, tracer burnout on the Mk46 was written as 800m in the manual… does it go to 1,000 from a 21”? Whats tracer burnout on the red tip?
Edit 2: I checked the 249 TM… doesn’t list tracer burnout, but does list max effective range on a area target at 1,000m. Better be shooting at a sizeable element to test that.
The penetration capability of the M855 is far superior to the M193. The 600 meter range (actually 640 meters) is for complete penetration of the NATO standard 3.45mm (0.136 inch) mild steel plate, for complete penetration of the M1 helmet the range is 1,300 meters. Hit probability reduces the effective range down a bit.
Penetration of a 9.5mm (3/8 inch) thick mild steel plate (20 in barrel):
M855 = 186 meters
M193 = 76 meters
Mk262 = 39 meters
Penetration of a 9.5mm (3/8 inch) thick mild steel plate (14.5 in barrel):
M855 = 131 meters
M193 = 37 meters
Mk262 = Cannot achieve complete penetration
EDIT - Tracer performance.
The requirement for M856 Tracer is for the trace to start no closer than 13 meters, and no further than 70 meters, and continue to be visible from an observer at the muzzle of the weapon to a minimum of 900 meters from a 20 inch barrel. Trace performance from the shorter barrel of a Mk46 will be reduced.
for complete penetration of the M1 helmet the range is 1,300 meters.
Its not that I doubt you, but have you seen this with your eyes? Punching Litz’s BC data for m855 shows an impact velocity of around 780fps at that range. Also, its going transonic at HALF that distance. Surely this worsens the BC, resulting in an even lower than predicted impact velocity? Maybe I’m grossly overestimating the ballistic resistance of that helmet?
Anyway, thanks for the schooling.
Its not that I doubt you, but have you seen this with your eyes? Punching Litz’s BC data for m855 shows an impact velocity of around 780fps at that range. Also, its going transonic at HALF that distance. Surely this worsens the BC, resulting in an even lower than predicted impact velocity? Maybe I’m grossly overestimating the ballistic resistance of that helmet?
Anyway, thanks for the schooling.
I think you are over estimating the strength of a helmet shell, and under estimating the value of a small diameter steel penetrator.
M80 ball will only reach out to 800 yards and penetrate a helmet.
I think you are over estimating the strength of a helmet shell, and under estimating the value of a small diameter steel penetrator.
M80 ball will only reach out to 800 yards and penetrate a helmet.
I’ll defer to your expertise. I learned some stuff; thanks.
On its best day, fired from a perfect rifle in a machine rest carriage, I don't think M855 can hit a helmet at 1000, much less penetrate it.
A steel plate the size of a truck, sure, easy to get a hit -- but a Soviet steel helmet? Color me dubious.
I'd like to see that requirement in print.
https://m.media-amazon.com/images/I/61GKoPbYVZL._AC_SY450_.jpg
Even 600 meters is a stretch. We're talking a target maybe 1.6 MOA wide and high.
On its best day, fired from a perfect rifle in a machine rest carriage, I don't think M855 can hit a helmet at 1000, much less penetrate it.
A steel plate the size of a truck, sure, easy to get a hit -- but a Soviet steel helmet? Color me dubious.
I'd like to see that requirement in print.
Even 600 meters is a stretch. We're talking a target maybe 1.6 MOA wide and high.
Completely agree.
On its best day, fired from a perfect rifle in a machine rest carriage, I don't think M855 can hit a helmet at 1000, much less penetrate it.
A steel plate the size of a truck, sure, easy to get a hit -- but a Soviet steel helmet? Color me dubious.
I'd like to see that requirement in print.
https://m.media-amazon.com/images/I/61GKoPbYVZL._AC_SY450_.jpg
Even 600 meters is a stretch. We're talking a target maybe 1.6 MOA wide and high.
I agree, but wouldn’t be surprised if they tested it by launching the M855 projectile at an extreme reduced velocity at a closer range. But how does M855 fly at 750fps? Point forward, or…?
Edit: mind you, the 1,000 meter max effective range listed in the 249’s manual is for an area target. Like I said earlier, better be shooting at a large formation to test that. Beaten zone and dispersion will be huuuuuge. Dope will require an astute observer and a T&E tripod.
I agree, but wouldn’t be surprised if they tested it by launching the M855 projectile at an extreme reduced velocity at a closer range. But how does M855 fly at 750fps? Point forward, or…?
Penetration is rarely actually carried out at the listed range, it is almost always done by reduced velocity tests, as angle of impact and location of hit on the target can be controlled much better.
Although, one of the first tests on M193 done in the late 1950s did include a 10 foot by 10 foot array of helmets, and a lot of bullets.
The current specification in STANAG 4172 is based on the NATO standard 10 gauge mild steel plate. However, in the FN report "5.56mm F.N. Ammunition for Machine Gun" dated 1976, they list the requiremets for the SS101 cartridge as:
"Specifications:- SS101 designed to penetrate US helmet with liner at 800 m range with a required minimum of 50% probability."
The objective of the new design [what would be the SS109] was increase the range by 40%, or better.
And, by the way, the M855 is quite stable.
https://i.imgur.com/5Nb7q67.jpg
Penetration is rarely actually carried out at the listed range, it is almost always done by reduced velocity tests, as angle of impact and location of hit on the target can be controlled much better.
Although, one of the first tests on M193 done in the late 1950s did include a 10 foot by 10 foot array of helmets, and a lot of bullets.
The current specification in STANAG 4172 is based on the NATO standard 10 gauge mild steel plate. However, in the FN report "5.56mm F.N. Ammunition for Machine Gun" dated 1976, they list the requiremets for the SS101 cartridge as:
"Specifications:- SS101 designed to penetrate US helmet with liner at 800 m range with a required minimum of 50% probability."
The objective of the new design [what would be the SS109] was increase the range by 40%, or better.
And, by the way, the M855 is quite stable.
https://i.imgur.com/5Nb7q67.jpg
Thanks for keeping this site great.
The current specification in STANAG 4172 is based on the NATO standard 10 gauge mild steel plate. However, in the FN report "5.56mm F.N. Ammunition for Machine Gun" dated 1976, they list the requiremets for the SS101 cartridge as:
"Specifications:- SS101 designed to penetrate US helmet with liner at 800 m range with a required minimum of 50% probability."
The objective of the new design [what would be the SS109] was increase the range by 40%, or better.
And, by the way, the M855 is quite stable.You're saying they shot, hit, and penetrated a US GI helmet at 800 with SS101, and 1,120 Meters with FN SS109 (both with a 50% penetration probability)?!
If so, I'm impressed and would like to see FN's data.
And, by the way, the M855 is quite stable.
We sometimes shoot with this retired P.D. LT who isn't THAT into shooting but has an AR and a 6.5 bolt gun with a couple of suppressors. Anyway, he just brings out M855 and shoots pretty darn good with his AR and a mediocre BDC reticle scope. He can hang pretty well out to 750 yards and more.
You're saying they shot, hit, and penetrated a US GI helmet at 800 with SS101, and 1,120 Meters with FN SS109 (both with a 50% penetration probability)?!
If so, I'm impressed and would like to see FN's data.
No, that is not how penetration tests are done.
First, you shoot a few dozen rounds and track them with radar and get an accurate velocity-range profile (in the old days, just calculate it).
Second, you set up you target at 100 yards*.
Then you shoot at the target, reducing or increasing the striking velocity until half of the shots, penetrate and half don't. This velocity is V50. You get results something like this:
https://i.imgur.com/5hWCaF7.jpg
You will note that there is some overlap, for the same velocities near V50 some will penetrate and some will not.
Compare V50 to your radar velocity plot and the range at which the bullet is traveling at V50 is R50, the range at which 50% penetration of the target can be expected. By further analysis of the data you calculate the V75, or any other probability of penetration you wish.
That system has been used for everything from 5.56mm to 16 inch naval guns, and is very accurate it establishing penetration performance. Sometimes you have to adjust the barrel twist to account for spin-down, but with small arms and their short time of flight, that is not an issue.
______________
* Or meters, if you are metric.
We sometimes shoot with this retired P.D. LT who isn't THAT into shooting but has an AR and a 6.5 bolt gun with a couple of suppressors. Anyway, he just brings out M855 and shoots pretty darn good with his AR and a mediocre BDC reticle scope. He can hang pretty well out to 750 yards and more.
Word of caution, don't confuse "stability" with "accuracy".
No, that is not how penetration tests are done...
This velocity is V50. You get results something like this:
... probability of penetration ...
That system has been used for everything from 5.56mm to 16 inch naval guns, and is very accurate in establishing penetration performance.Ah, thank you. Lies, damn lies, and statistics. :)
Knowing how Green Tip performs (even out of good barrels and rifles) I always thought what they were selling reference M855 precision at range was bullshit.
Word of caution, don't confuse "stability" with "accuracy".
I don't follow. I'm sure his gun is 1/7 twist. Stability isn't an issue.
I don't follow. I'm sure his gun is 1/7 twist. Stability isn't an issue.
I think he means in the transonic-subsonic zone, since I mentioned I wasn’t sure it would be point-forward there.
I think he means in the transonic-subsonic zone, since I mentioned I wasn’t sure it would be point-forward there.
Ahhh.. Got it.
I don't follow. I'm sure his gun is 1/7 twist. Stability isn't an issue.
Well, I had just noted that M855 was particularly stable. You immediately quoted with an example of M855 showing accuracy.
While the gentleman may be able to shoot M855 accurately, accuracy and stability do not go hand-in-hand.
In order to have any sort of accuracy, the stability factor must be greater than 1.00, other than that stability does not govern accuracy. The M193 55 grain bullet, out of a 1-12 twist barrel has a stability factor of 1.28, and is generally more accurate than the M855 which has a stability factor of 2.32 out of a 1-7 twist barrel. And, the 175 grain .308 Sierra match from a 1-10 barrel with a stability factor of 2.00 is more accurate than either.
As to the trans-sonic region, I think many people are confused why this zone is important.
Bullets, if stable at supersonic speed will remain stable through the trans-sonic region into the subsonic region. The forces on the bullet due to air pressure are what become unstable as the shock wave dissipates, and coupled with the very high drag in the trans-sonic region and the variation in range at which the bullet encounters this high drag (due to small variations in muzzle velocity) tend to increase the dispersion.
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