On a plain old 5.56 chambered, Chrome lined, standard combat barrel... is there a bad or unsafe amount of leade?
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On a plain old 5.56 chambered, Chrome lined, standard combat barrel... is there a bad or unsafe amount of leade?
I don’t think it will become unsafe but the accuracy can drop off severely.
On a GI 5.56 barrel, no. Colt and FN barrels are throated long. As they wear the throat gets longer. Not necessarily unsafe but as you start getting gas blow-by and bullet free-jump (the space between the case neck and where the bullet ogive starts engraving on the leade on each land) you're not going to get the best accuracy out of that weapon.
Even with single-loaded 80-grain Sierra Match Kings the bullet ogive ain't going to touch unless that sucker's loaded WAAAAAAY long.
Off the top of my head a short-throated National Match rapid-fire barrel will mic cartridge overall length about 2.445 - 2.450 long. A USAMU Match throat is 2.500. A Colt or FN MILSPEC M16 or M4 is 2.500 to 2.550.''
If you borescope your weapon you'll see the throat show gas cracking and chrome wear advancing from the start of each leade along the top of each land about .001" per thousand rounds.
Load it up and shoot it.
OK. So I was looking at the 5.56 chamber drawing. It shows .146 leade.
I have pretty old bushy barrel that has a bullet jump of .177". Now that thing probably didn't start out with a mil spec leade. I'm just trying to get an idea if the barrel has a lot of life left in it.
If working with 5.56mm NATO layout, you could try to dredge up a barrel erosion gauge and just measure instead of guestimating.
Pull the BCG, drop the tool through the receiver into the bore and if it's a go, then all if fine, if it's beyond the limit line on the tool, its basically shot out.
http://pics.gunbroker.com/GB/2201120...x550880306.jpg
You could ask IG if he has a barrel erosion gage and check it for you.
A barrel erosion or throat gage is quick (it really doesn't tell you much).
A Stoney Point gage is better (you can gage the throat with the actual bullets you shoot instead of just a nominal gage diameter).
Borescoping gives you a visual.
Best performance standard is to actually shoot the weapon and determine if it meets your expectations.
Most folks who will NEVER shoot past 100 yards/meters it ain't going to matter. An IPSC or E-type is very forgiving.
If you plan on shooting further than 100 then you have to look at group size. Is a 2-8 inch circle at 200 OK for you? Is just hitting ANYWHERE on the target OK?
For me and a rifle or carbine if I'm not hitting on-call at 200, 300, and further then I need a new barrel. I can't stand shots off-call where I have no idea why the rounds or groups went there, or the groups are unexplainably big.
Barrels are a consumable. With a vise, action blocks, a wrench, and a headspace gage I can change one out in just a few minutes.
Scrub it clean. Shoot it until accuracy goes away, by whatever measure you use. Replace it.
I've seen barrels lose accuracy at 5K, and some still hold acceptable (minute of bad guy) past 15k.
If you're worried that it might go away any time soon, and you don't want to be caught short, then it is a simple calculation for you: balance the peace of mind of a new barrel, against the cost for same.
Only you can tell you how much cost is too much.
Hey, Patrick.
Good to see you post on here. I enjoy your handguns episodes with Aaron Rogers.
How is .177" guestimating? :confused:
The barrel seems to shoot good still. And yes, I do shoot it out to 400 plus yards on occasion... but usually on gongs... so I don't know what the groups are looking like.
I'm kind of wondering if the .177" is an alarming amount or just a small piece of the whole picture.
For comparison, I measured my brand new FNMI M16 barrel, and it was in the 140s. That's why I checked the diagram... I didn't know a 5.56 chambered barrel had that much leade from the get go.
Yeah. I remember you mentioning that there aren't any very good throat guages.
Pacific Tool and Gage makes a good one (sold through Midway),
http://media.midwayusa.com/productim...153/153245.jpg
as does Merchant (sold through Brownells).
http://www.brownells.com/userdocs/sk...65017223_1.jpg
AFSOC Chief Master Sergeant Gary Crane used one to check my rifle to let me know he thought one of my barrels was worn out -- just before I earned a Bronze Excellence-in-Competition leg medal at the Atlantic Fleet Match.
Two months later we got to Camp Perry and I shot like I'd never held a rifle before. I knew I don't suck that bad.
Derrick Martin at Accuracy Speaks checked my barrel again (a Douglas 1-8 stainless) and told me it was past toasted.
Round count was around 3,000, and after going through data books and scores it looks like it died around 2,400 rounds when I started getting wide groups at 300 and unexplained fliers at 600.
Accuracy on a stainless drops off like a cliff once its throat goes. Accuracy on a chro-moly match or chrome-plated GI chrome-vanadium tapers off slowly.
Description here: http://www.superiorbarrels.com/Throa...on%20Gages.htm
Quote:
The AR Master Caliber Gage is designed especially for the AR family of rifles. The Service Rifle teams gage their rifles often because they want to know exactly where they are as far as barrel life is concerned. They know at what point their rifles are about to lose top accuracy and when to replace their barrels. Military depots use erosion gauges to determine if the rifle needs to be rebarreled or just refinished.
The top long range and course shooters also keep close watch on their barrels using erosion gauges. Shooters, who load their own ammunition, with the proper use of this gage, can get more barrel life out of their ARs by knowing exactly where their throat is located. Shooting the AR without an erosion gage is like having a car without a working mileage meter and guessing when you should change your oil.
The military M16 gage has only one reading: REJECT. Other than that, it is anyone's guess as to exactly where you are in the life of your barrel. What is not widely known is that the REJECT point on the military gage is the point where the M16 shoots 7.2" groups or larger at 100 YARDS! Obviously, this is not acceptable to the match shooter. In addition, the M16 gage is designed to gage chrome lined bore ONLY.
Ideally, the AR Master Gage is first used on a new barrel and the reading recorded in your Round Life Data Book. Top shooters keep meticulous records on exactly the number of rounds they have fired through their barrels. If you are not keeping these records, REMEMBER THERE IS NO REJECTION RING ON THIS GAGE.
The AR Master Gage has been calibrated against a new Colt AR-15 Heavy barrel and cross referenced with a after market chrome lined barrel as well. A new barrel should gage at or about the fourth ring on the gage (See reading the Gage below). However, since there is a wide variation of barrel manufacturers out there you may see different readings on a new barrel. For this reason additional Witness Rings have been added in case you have a shorter than normal throat. One new barrel checked read only two rings at -0- rounds and may read as low as the first ring. You do not know until you check.
The AR Master Gage has several unique design characteristics. First off, there are enough rings to gage the useful life of any barrel, and you can trace the throat wear up until the point it fails.
There is a support shoulder on the gage. As the gage is placed in the chamber, the support shoulder will rest on the rear of the chamber and keep the gage at or near the middle of the upper receiver group. This assures you do not get a false reading by having it canted excessively.
You will note the gage is tapered. This allows it to find the location of the front of the throat so you will know how much more the bullet has to jump before it takes the rifling.
The AR Master Gage is precision made of stainless steel. With proper care, you will be able to pass this gage on to your children for their rifles. Always replace the protector cap when not in use to protect the point of the gage. Gauges are no better than their care.
http://www.fulton-armory.com/%5Cfaqs...s%5CT-gage.gifQuote:
The Master Caliber Throat Erosion Gage can be one of the Competition Shooters most valuable tools. First off, most shooters have seen the military erosion gauges for the M14 rifles or perhaps the gage for the M16 family. These gauges are mostly useless for the civilian family of firearms because these gauges are calibrated to determine the wear/rejection point of chrome lined bores. For instance, the Rejection Point rejection point on a M14 gage is 8.8 inches, a M1 Garand is 8.0 inches, and on an M16 is 7.2 inches at 100 yards with ball ammunition, which is about 10,000 rounds. Obviously to the competitive shooter, the rifle barrel should have been replaced well before that point. Military ammunition is also loaded under very controlled conditions: the same bullet weight, ogive, diameter, and to the same length. Another point to remember is military propellant has been thoroughly tested to insure it does not exhibit excessive erosive qualities while civilian propellant generally have no such controls.
The military gage is not applicable to civilian competition shooters for several other reasons.
1. A wide variety of commercial barrel designs exists that varies in diameter from a minimum diameter of .298 to .3015 in the 30-caliber family alone. Chrome moly, stainless, and the other barrel materials will affect the erosion progression as well. The variation in diameter on two barrels cut with the same reamer and zero rounds will give as much as three rings variation.
2. The civilian chamber can also have a large variety of throat variation. Some reamers are custom made for as little as .025" freebore all the way to .150" freebore. This variation will give 1 to 2 rings variation.
3. Civilian barrels can be two groove to six groove which will give different readings as well. Civilian barrels have no performance requirement insofar as barrel life is concerned. Recently observed was a somewhat new commercial barrel that "went out" at 700 rounds requiring setback and rechambered with a short throat reamer. Close examination and erosion gage readings taken. On the second run the barrel went for 1100 rounds and went out again at which time it was sectioned and found to have the rifling burned away for approximately ¾" in front of the chamber. This barrel was never exposed to a rapid-fire string and was always fired slow-fire strings with 150 to 168 grain Sierra bullets.
4. The military style gage is designed for one rifle and one caliber and cannot be used for other calibers, i.e. 7.62 Gage cannot be used in 30.06 or other calibers such as magnums.
How is this gage used? Ideally, your Master Caliber Throat Gage is GENTLY INSERTED into the bore. Care should be taken to keep the gage centered to give repeatable readings. It is precision polished to match the throat so it will not scratch or scar the barrel. Looking down from directly above the action watch as the gage is inserted. Count the rings as they disappear under the receiver bridge. To make things easier every fifth ring is extra wide. Therefore, if you pass the first heavy ring and then proceed two more you are at 7 rings or part thereof, i.e. 7 1/3 rings, 7 ½ rings etc.
If you have a new-barreled action, take time to record this reading in your notebook as -0- rounds. Then every 500 or 1000 rounds take additional readings and record how much further the gage follows the throat erosion down bore. On 30-caliber government barrels with government ammunition, the erosion progresses at approximately 0.100" per 1000 rounds. The rings are evenly spaced each .100" apart regardless of caliber.
If you are using this gage on a used barrel for the first time record the reading at the number of rounds you have fired. For instance, your reading is 8 rings at 835. At 1835 rounds, you take the reading again and determine how far the gage now goes into the barrel. If it has increased one ring in one thousand rounds, you pretty well know what it is going to read at 3835 rounds. To make it simpler, take an additional reading at an even point such as 500, 1000 rounds and you can pretty well guess what your barrel was when it was new.
If you are using propellant that is hotter than the propellant loaded by the government or you are using heavier bullets etc., in all probability, your readings will vary. Many people rebarrel at a certain number of rounds but the barrel may not be eroded to the point you need a new barrel. For instance if you have selected the bullet, primer, propellant combination that gives less than average erosion you can get much more life out of your barrel.
If you observe the ring readings increasing, you should know to seat your bullets further forward to be up close to the rifling. Many people use a loaded round seating it out further until it touches. This is a dangerous practice and is to be avoided. The erosion gage is fast, easy and accurate. No guesswork, if the ring reading has increased one ring, you seat depth is going to follow appropriately. Each bolt gun action is different from the throat to the front bridge opening as well. Therefore, this gage is useable in Remington, Winchester, Springfield, Enfield, and other actions in those calibers for which the gage is designed.
You need only one gage per caliber. For instance the 30 cal. Gage can be used with the bolt rifle in calibers from 303 British, 308 Winchester, 30.06 all the way to the 300 Win. Mag. cartridge. Wildcat cartridges are also measurable, thus the multiple rings. Remember in the longer calibers 30.06, 300 Win. Magnum you will count more rings before the gage finds the throat and comes to a stop. Thus, the heavy ring every fifth segment to make it easier to read.
The 6MM Gage will record readings from the 6 BR to the 6/284 cartridge. The 6.5MM gage will fit 260 Remington to 6.5/284. The 7MM gage will fit 7BR to 280 Remington.
There are two types of 22 center fire gauges. The first will fit bolt rifles in calibers 222 Remington to 220 Swift. The other one is for the AR-15 service rifle. The basic difference here is where the gage is read. Bolt guns will be read as above. The AR family of rifles is read from the rear of the upper receiver. While the rifle is broken down for cleaning, gently insert the AR gage while looking across the rear of the upper receiver group. As the rings disappear into the upper group, count the rings. Keep a log of what you detect. Make sure to keep the gage centered in the upper bolt way.
These gauges are precision made instruments and should last a lifetime if properly cared for. You can pass this gage on to your children. The great advantage of this gage is they are stainless steel so they are less likely to rust giving false readings. A very durable carry case can be fabricated by the owner for pennies. A half inch piece of PVC water pipe with one cap glued in place and the other slipped on will protect your gage for years. The design of the gage takes into consideration it will be accidentally dropped or dinged on the point. If this happens just take a fine whetstone and dress up the point as little as possible. The critical contact point is approximately 1/8"from the actual point. The point is .002 to .003" smaller than the smallest bore to add this protection.
Never mind.