View Full Version : Understanding Cyclic Rate
This is really a noob question, but after all of my reading and searching, I have never found an answer to this. M4 feed ramps are said by many to only be necessary for an SBR on full auto. My question is why and how would a closed rotating bolt system have a faster cyclic rate SHOT PER SHOT in full auto as opposed to semiauto? In the time frame of: firing pin hits primer, round fires, BCG cycles, new round is chambered, STOP. In that one round cycle why would it happen faster (if it does) in full auto vs. semi?
If you were to take the elapsed time for one round to fire, cycle and chamber another round out of an M4A1 on semi, then multiply that time by 30 would it be the same amount of time to fire a 30 round mag on full auto? If noy why?
I have read of “bolt bounce” but really don’t understand how that comes into play with a locking action. If it is the same speed, then wouldn’t M4 feed ramps just as "necessary" in a 6921 as they would be in an M4A1?
I’ve been doing some searches and have looked back a few years where some reputable members of this site have even said that M4 ramps were not necessary in a semi auto. It is not really an issue since any MFG I would buy from uses M4 ramps as standard, but I have always been curious about the reasoning for this, given the above. If this has been covered please point me to a link/resource. Thanks.
Who are many? It is my understanding the M4 feed ramps were a reliability upgrade to improve feeding with M885 and the occasional magazine issue. They wouldn't really have an effect on cyclic rate except friction of chambering a round in the bolt locking cycle (negligible).
Your other question doesn't have as much to do with the moving parts of the system as it does with the fire control group. Auto sears can be timed to let the hammer go at a specific point. The disconnector wont let you fire until a specific point in semi auto. Whether or not one is faster than the other I couldnt tell you.
Edit: The above part figures "all things being the same" as in gas system, buffer weight etc. Those things are what effect the unlocking time of the bolt and it's rearward/forward movement. The timing of the FCG is dependent upon the movement of the BCG. I was figuring since you specifically asked about semi-auto vs full auto mode it was a question about the "same" rifle, not different styles.
Most of the "many" are understandably trying to justify their "right of chart" purchase, but I have also heard this by some seamingly sound individuals. I believe Larue discounts M4 feedramps as being only for full auto.
From what I have read, I agree with you on the general mag/reliability issue, but it is always the FA issue that gets blamed for the existance of M4 ramps. If the BCG speed travels at the same speed per cycle then I don't see how FA is an issue vs. SA. In this context sear adjustment etc. should not matter. Neither will fire until the bolt is fully locked over a chambered round, correct?
Remember the AR platform is a system. Other things that will affect the cyclic rate are buffers, the size of the gas port and the size of the system (rifle, carbine, mid length).
When I switched from my UBR set up with H3 buffer to the Vltor A5 with heavy buffer I could tell a difference.
IG,
I'm talking about a Colt 6921 vs. an M4A1, or even the same M4A1 firing on auto vs. firing on semi, so there is no variation in weapons setup. Is a single cycle of the bolt faster on auto vs. semi or is this myth? The answer would seem obvious to me, but I honestly just don't know much about this platform in FA configuration, and as I said some credible people seem to infer that there is a difference.
Sorry, misunderstood. I wonder if it's true as well. I hadn't really heard or thought much about it to be honest. Maybe it could be because of the momentum of the BCG once it starts firing in auto?
IG,
I'm talking about a Colt 6921 vs. an M4A1, or even the same M4A1 firing on auto vs. firing on semi, so there is no variation in weapons setup. Is a single cycle of the bolt faster on auto vs. semi or is this myth? The answer would seem obvious to me, but I honestly just don't know much about this platform in FA configuration, and as I said some credible people seem to infer that there is a difference.
Most of the "many" are understandably trying to justify their "right of chart" purchase, but I have also heard this by some seamingly sound individuals. I believe Larue discounts M4 feedramps as being only for full auto.
From what I have read, I agree with you on the general mag/reliability issue, but it is always the FA issue that gets blamed for the existance of M4 ramps. If the BCG speed travels at the same speed per cycle then I don't see how FA is an issue vs. SA. In this context sear adjustment etc. should not matter. Neither will fire until the bolt is fully locked over a chambered round, correct?
AR-15s cannot (this is debated) fire out of battery so yes it has to be locked. It would lock at the same speed in semi as in full.
My logic was everything being the same (buffer weight, springs, gas system) that the only thing that could effect cyclic rate is the FCG. The hammer can be adjusted to fall earlier in the locking cycle which would increase the cyclic rate (right up until the point the hammer would be following the movement of the BCG).
IG,
That seems to be the common reasoning, but I just can't make that work in my mind with a locking bolt. On an open bolt type weapon I could understand, but not an M4.
Like I said, I do not have the knowledge to give any kind of real opinion on this, but cyclic rate in full auto seems to be a common excuse for needing/not needing M4 ramps. I am hoping to get some facts on this.
AR-15s cannot (this is debated) fire out of battery so yes it has to be locked. It would lock at the same speed in semi as in full.
My logic was everything being the same (buffer weight, springs, gas system) that the only thing that could effect cyclic rate is the FCG. The hammer can be adjusted to fall earlier in the locking cycle which would increase the cyclic rate (right up until the point the hammer would be following the movement of the BCG).
I'm tracking you on the first part, but I think you are still talking about a burst or string of fire on FA. I am just talking about the time it takes to cycle one round, whether in the middle of a FA mag dump or a single SA shot. In both of these cases the hammer will only fall and be pushed back one time. Why would one be faster than the other?
I'm tracking you on the first part, but I think you are still talking about a burst or string of fire on FA. I am just talking about the time it takes to cycle one round, whether in the middle of a FA mag dump or a single SA shot. In both of these cases the hammer will only fall and be pushed back one time. Why would one be faster than the other?
I got off track into theoretical cases, you can do a lot with a trigger group but I don't think it applies to your question. There is no conservation of momentum in full auto, the bolt has to lock and stop so yes it is the same speed (assuming same gun, same ammo, same conditions).
Edited to add: To the best of my knowledge.
Redacted in its entirety. See SME below.
Grumpy MSG
03-22-11, 09:23
Let me offer my .02 on this discussion:
The M4 feed ramps were designed to improve reliability with a higher cyclic rate weapon. It is not about semi versus auto. It is actually the carbine length gas system versus rifle length gas system and gas port size combined with gas port erosion (the port getting bigger, increasing the effective cyclic rate0. The M4 is notorious for getting faster as the barrel wears out with some weapons exceeding 1000 rounds per minute as they approach the end of the barrel life. Whether that particular rifle is fired in semi or on auto/burst, that bolt will slide to the rear at the same speed, stop and go forward, stripping the next round from the magazine and chambering it at the same speed.
I am going to just make up numbers to explain the difference, at 600 rounds per minute it takes 1/10 of second for that action to cycle. At 1200 rounds per minute it is 1/20 of a second or twice as fast. Now the AR/M4 family is faster than the lower rate and wore out when it approaches the upper. You have to understand that as you speed up the movement of the bolt to the rear, stopping and returning forward, you reduce the amount of time the next round has to position itself in the magazine, meaning it may not be perfectly aligned against the lips when the bolt comes back forward. The M4 feed ramps offer a bigger area to slap the tip of the bullet and shove it into the chamber.
Efforts to slow down the cyclic rate include the Enidine buffer, use of the heavier buffers, changing the gas port size, adjustable gas ports, the "fatboy" gas tubes and I have even seen someone use a rifle gas tube with a loop in it, bent and tucked under the handguards trying to slow it down.
Now if you want to build the most accurate shooting weapons, like Larue does. you can understand why shoving a bullet into a steeper feed ramp might not lead to optimal accuracy.
lifebreath
03-22-11, 10:36
Let me offer my .02 on this discussion:
Thank's for your insight. Your response makes a lot of sense and is worth more than two cents. I was not aware that the gas port erodes like that with use.
Grumpy nailed. I would only add that the lowered M4 ramps also allow the rounds to enter from a lower position. One problem with the M4 on full auto is the magazine sometimes cannot lift the rounds fast enough to feed reliably. Having the lowered M4 allows the tips to be guided from a lower position
Grumpy nailed. I would only add that the lowered M4 ramps also allow the rounds to enter from a lower position. One problem with the M4 on full auto is the magazine sometimes cannot lift the rounds fast enough to feed reliably. Having the lowered M4 allows the tips to be guided from a lower position
Absolute BS! You couldn't prove this both hands and a flashlight. Grumpy is about half right but the fact is this subject, like many others, will never be settled so why bother.
Grumpy nailed. I would only add that the lowered M4 ramps also allow the rounds to enter from a lower position. One problem with the M4 on full auto is the magazine sometimes cannot lift the rounds fast enough to feed reliably. Having the lowered M4 allows the tips to be guided from a lower position
Here we go with the full auto again. MistWolf, I'm not trying to pick on your post but it is statements like yours above that lead me to create this entire thread. Look at what the Master Sergeant said:
[Whether that particular rifle is fired in semi or on auto/burst, that bolt will slide to the rear at the same speed, stop and go forward, stripping the next round from the magazine and chambering it at the same speed.]
If this is the case, then why would full auto on an M4 cause any feeding problems that semi would not? If the bolt is traveling at the same speed, why would it matter if you were firing a single shot or doing a full auto mag dump?
Absolute BS! You couldn't prove this both hands and a flashlight. Grumpy is about half right but the fact is this subject, like many others, will never be settled so why bother.
Um... http://en.wikipedia.org/wiki/Hooke%27s_law and I didn't even need a flashlight.
Um... http://en.wikipedia.org/wiki/Hooke%27s_law and I didn't even need a flashlight.
Not even going to waste my time looking. It is impossible for the bolt group to outrun a properly functioning magazine, period.
Not even going to waste my time looking.
*golf clap* o.O
Not even going to waste my time looking. It is impossible for the bolt group to outrun a properly functioning magazine, period.
Fine edit your entirely sarcastic post to add a caveat. The parameter of "properly functioning" means that it functions. If it didn't function, then it would not be "properly functioning."
Grease Monkey
03-22-11, 20:16
Great post Grumpy!
Thanks MSG and everyone that provided some info. I do not want this to degrade into a mag/feedramp thread though. I asked a very specific question regarding bolt speed, and am a little bit surprised at the lack of answers/data here, and on the internet as a whole. Many people clearly claim that full auto on an M4 causes some sort of feeding problem (unrelated to heat, wear, etc.) that does not happen in semi auto.
While I appreciate the dialogue, his thread is not intended to be "M4 ramps 101" in any way. I believe there is a great deal of educational value in having this question answered and would appreciate my thread not being muddied up with superfluous bullshit.
A real answer to this question should make all of the mag/ramp issues either completely moot or completely valid when speaking of a civilian carbine. Again, I really appreciate any info from a SME on this.
MSG gave a pretty concise answer. You are looking for a yes/no answer to an incremental question.
Without outside interference the only way to change the velocity would be to change the forces, mass or distance in fully auto vs semi auto mode. Outside interference would be heat, wear, friction etc., the things that normally effect feeding in any case.
Design history is usually important. M16A4s apparently don't have the extended feedramps and are full auto. Which would point to it being an issue with the carbine gas system. CAR17s had slightly extended ramps, which would also support it being a carbine issue.
Absolute BS! You couldn't prove this both hands and a flashlight. Grumpy is about half right but the fact is this subject, like many others, will never be settled so why bother.
Bolt speed isn't faster because the weapon is being fired in full auto.
Magazine not keeping up with the full auto carbine is not just because the bolt speed but the time from shot to shot is less when firing full auto than when firing semi-auto. Perhaps I made a mistake in saying "magazines" when it would be more accurate to say "some magazines".
If it's BS, then so be it. It's something I picked up following the various stickies, threads and links on this site. It was pointed out the feed problems the M4 ramps were to fix didn't show up until ARs were cut down to carbine length and fired full auto, usually with magazines with weaker springs
Grumpy MSG
03-23-11, 07:53
Bolt speed isn't faster because the weapon is being fired in full auto.
Magazine not keeping up with the full auto carbine is not just because the bolt speed but the time from shot to shot is less when firing full auto than when firing semi-auto. Perhaps I made a mistake in saying "magazines" when it would be more accurate to say "some magazines".
If it's BS, then so be it. It's something I picked up following the various stickies, threads and links on this site. It was pointed out the feed problems the M4 ramps were to fix didn't show up until ARs were cut down to carbine length and fired full auto, usually with magazines with weaker springs
NEVER, NEVER take anything somebody says on here personal. Some folks just think they are better/ smarter than everybody else on here. You have no way of knowing whether I know what I (or anybody else) am talking about. Just read it, think about what someone writes and if it makes sense, add it to your book of knowlege. If it smells like horse manure, it might be and throw it in the garden not your book of knowledge.
Thanks MSG and everyone that provided some info. I do not want this to degrade into a mag/feedramp thread though. I asked a very specific question regarding bolt speed, and am a little bit surprised at the lack of answers/data here, and on the internet as a whole. Many people clearly claim that full auto on an M4 causes some sort of feeding problem (unrelated to heat, wear, etc.) that does not happen in semi auto.
While I appreciate the dialogue, his thread is not intended to be "M4 ramps 101" in any way. I believe there is a great deal of educational value in having this question answered and would appreciate my thread not being muddied up with superfluous bullshit.
A real answer to this question should make all of the mag/ramp issues either completely moot or completely valid when speaking of a civilian carbine. Again, I really appreciate any info from a SME on this.
Let me try this again: Given a particular M4 carbine, the bolt moves back and forth at the same speed, whether it is on semi or auto/burst. The M4 feeding issues are more pronounced when it is fired on auto than when it is fired on semi. They are still there, just less noticeable. The rifle length gas system has a lower cyclic rate so therefore less issues.
Not even going to waste my time looking. It is impossible for the bolt group to outrun a properly functioning magazine, period. .
If there were never magazine related problems with the M16/M4 family, the Military would still be using the magazines with the black followers. The green and now sand/tan colored followers in Mil Spec magazines wouldn't exist now would they? The Magpul followers and PMAGs wouldn't exist if there wasn't an issue that needed to be addressed.
If there were never magazine related problems with the M16/M4 family, the Military would still be using the magazines with the black followers. The green and now sand/tan colored followers in Mil Spec magazines wouldn't exist now would they? The Magpul followers and PMAGs wouldn't exist if there wasn't an issue that needed to be addressed.
:suicide:
Citing Wikipedia, a source in which any halfwit can go in and change the core information at will, is pretty much an automatic no-go if one wants to refer to scientific and technical ANYthing. I wouldn't bother to click on a Wiki link, either.
That crap changes like the tides because some emo hipster that isn't satisfied with passing the time by cutting him/herself and smelling bad decides to go online and start dicking with Wiki...what they alter might get caught and brought back to center. Might not.
I believe that "Wikipedia" is an ancient Algonquin word that freely translates into "instant loss of credibility."
There's far, far better source material. Plenty of online higher-institution research libraries around to pull from...
NEVER, NEVER take anything somebody says on here personal...
No worries there, mate:D
I believe that "Wikipedia" is an ancient Algonquin word that freely translates into "instant loss of credibility."
A sig worthy gem right there
The issues with magazines were evident well before the M4 carbine was type classified.
Aluminum magazines can be damaged and not noticed. Also many soldiers are not even taught on how to properly inspect magazines. This is why you have dented feedlips and bodies which lead to malfunctions.
The updated followers were improvements made to prevent rounds from dipping inside the magazine. There is no "voodoo" it's just a simple evolution of a design and people realizing there was a problem.
It had ZERO to do with the M4 or ful auto. IMHO. Did I mention that aluminum magazines weren't supposed to be continually re-used over and over?
Citing Wikipedia, a source in which any halfwit can go in and change the core information at will, is pretty much an automatic no-go if one wants to refer to scientific and technical ANYthing. I wouldn't bother to click on a Wiki link, either.
That crap changes like the tides because some emo hipster that isn't satisfied with passing the time by cutting him/herself and smelling bad decides to go online and start dicking with Wiki...what they alter might get caught and brought back to center. Might not.
I believe that "Wikipedia" is an ancient Algonquin word that freely translates into "instant loss of credibility."
There's far, far better source material. Plenty of online higher-institution research libraries around to pull from...
Hooke's Law is first year physics. Maybe I shouldve just posted a rant instead? Wikipedia was the first hit on google. I don't have a citation because I don't need a book to remember stress is proportional to strain. This should cover it though: Principles of Engineering Mechanics Millard F. Beatty, 1986
Grumpy MSG
03-23-11, 18:58
The issues with magazines were evident well before the M4 carbine was type classified.
Aluminum magazines can be damaged and not noticed. Also many soldiers are not even taught on how to properly inspect magazines. This is why you have dented feedlips and bodies which lead to malfunctions.
The updated followers were improvements made to prevent rounds from dipping inside the magazine. There is no "voodoo" it's just a simple evolution of a design and people realizing there was a problem.
It had ZERO to do with the M4 or ful auto. IMHO. Did I mention that aluminum magazines weren't supposed to be continually re-used over and over?
No argument that magazines were a weakness before the M4.
As for maintaining magazines, just like anything some Soldiers do it, some don't. Some units keep all the magazines in the arms room and issue them when the unit goes to the field and they turn them in afterwards (those are the ones I suspect receive absolutely no maintenance 90% of the time). Other units have bad magazines identified and turned in to the supply sergeant, only to have them issued to another Soldier. It got so bad with one unit I dealt with, my policy was to take the identified magazine from the Soldier at the range and stomp the crap out of it insuring it wouldn't be issued again. Time and again that unit would send those Parsons magazines that were identified in P.S. Magazine in the early '90s to the range and they would fail to feed with 5-6 rounds left in the magazine. After a year or two the problem was solved. As for the endless service life, I pin that on the folks who seem to gravitate to the supply MOS, we had one Supply Sergeant who was the butt of a lot of jokes, and actually said to NCOs "If I give you those Chem-lights, I will have to order more.", when he eventually left the unit we got those Chem-lights, they were out of date by then and wouldn't half glow.
IMHO magazines do have everything to do with the M4/ M16 on semi and full auto. without a magazine the M4/M16 is a single shot rifle, if a magazine fails to do it's job, the rifle will fail to function correctly. There is a reason that Slap up on the magazine is the first step in SPORTS.
Certainly no need for a rant, just a need to choose one of the many links with a .edu suffix (on the same Google page, one may notice, and the next, including one from Stanford) instead of a source where the explanation of Hooke's Law couldn't be easily replaced by somebody's favorite remoulade recipe.
Point being: Don't razz another member for not wanting to look at your source when your source is the academic-integrity equivalent of Milli Vanilli. Take the time to choose a better source in the future.
Certainly no need for a rant, just a need to choose one of the many links with a .edu suffix (on the same Google page, one may notice, and the next, including one from Stanford) instead of a source where the explanation of Hooke's Law couldn't be easily replaced by somebody's favorite remoulade recipe.
Point being: Don't razz another member for not wanting to look at your source when your source is the academic-integrity equivalent of Milli Vanilli. Take the time to choose a better source in the future.
This is a gun forum, I'd expect Stanford to have about as much credibility as wikipedia. :p
Grumpy MSG
03-23-11, 19:15
Certainly no need for a rant, just a need to choose one of the many links with a .edu suffix (on the same Google page, one may notice, and the next, including one from Stanford) instead of a source where the explanation of Hooke's Law couldn't be easily replaced by somebody's favorite remoulade recipe.
Point being: Don't razz another member for not wanting to look at your source when your source is the academic-integrity equivalent of Milli Vanilli. Take the time to choose a better source in the future.
Darn you are good, I never could have figured out how to squeeze Milli Vanilli into a gun post...:lol::lol::lol:
I wholeheartedly agree about the whole supply thing. Unfortunately it is an issue with all of the branches of the military.
No argument that magazines were a weakness before the M4.
As for maintaining magazines, just like anything some Soldiers do it, some don't. Some units keep all the magazines in the arms room and issue them when the unit goes to the field and they turn them in afterwards (those are the ones I suspect receive absolutely no maintenance 90% of the time). Other units have bad magazines identified and turned in to the supply sergeant, only to have them issued to another Soldier. It got so bad with one unit I dealt with, my policy was to take the identified magazine from the Soldier at the range and stomp the crap out of it insuring it wouldn't be issued again. Time and again that unit would send those Parsons magazines that were identified in P.S. Magazine in the early '90s to the range and they would fail to feed with 5-6 rounds left in the magazine. After a year or two the problem was solved. As for the endless service life, I pin that on the folks who seem to gravitate to the supply MOS, we had one Supply Sergeant who was the butt of a lot of jokes, and actually said to NCOs "If I give you those Chem-lights, I will have to order more.", when he eventually left the unit we got those Chem-lights, they were out of date by then and wouldn't half glow.
IMHO magazines do have everything to do with the M4/ M16 on semi and full auto. without a magazine the M4/M16 is a single shot rifle, if a magazine fails to do it's job, the rifle will fail to function correctly. There is a reason that Slap up on the magazine is the first step in SPORTS.
Grumpy MSG
03-23-11, 20:42
This is a gun forum, I'd expect Stanford to have about as much credibility as wikipedia. :p
"I don't care who ya are, that's funny right there!" I can't say it better than Larry the cable guy...
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