Okay gurus and brain trust, I have an AR gas system question.
As I understand it, there is an "ideal" cyclic rate, which is to say there is an ideal bolt velocity. If the bolt velocity is too low, you can see things like failure to strip off a new round, failure to lock open, or even stove pipes. Things that could contribute to this could be weak ammo not generating enough gas pressure, gas port drilled too small, gas system length not correct for application (dwell time too short), or BCG/Buffer too heavy.
So from a physics perspective, I see two major groups of components. All the pressure generating aspects (strength of ammo, gas system sizing/length) which determine how much force is applied to the BCG, and then there is the weight + spring rate of the BCG+Buffer+Buffer_Spring. If you change something to generate more gas/pressure, more force is applied to the BCG and your bolt velocity goes up. If you reduce weight in the BCG+Buffer, or reduce spring rate, bolt velocity should go up. And visa versa.
Why would it be better to change the gas system versus changing the reciprocating weight? Assuming either change results in obtaining the ideal bolt velocity.
I am working on 10.5" barrel, carbine length gas system, with an M16 bolt carrier, in 7.62x39. The primary goal of this build was being able to train with cheap steel ammo (Wolf 122g and the like). I have worked my way through feed ramp issues, and magazine issues. I am now confident that I have a (low) bolt velocity issue. I originally built it with an H2 buffer, and it was a complete train wreck. It wouldn't lock the bolt back on an empty mag with any ammo. Once I went to a standard weight buffer, it would lock back on silver bear ammo, but not reliably on wolf. The silver bear ammo fed quite reliably, but with wolf, I would get frequent failure to feed, where there was no jam, just no round in the chamber. Rack it and it was back in action. I tried modifying a standard carbine buffer by replacing one of the standard steel weights with aluminum. It ran a little bit better on the wolf ammo, but still has an occasional failure to feed which appears to be due to short stroking.
So it looks like my options are:
A) Open up the gas port to get more gas flowing, doing it perfectly.
B) Open up the gas port to get more gas flowing, overshoot, then have to add an adjustable gas block and or a heavier buffer
C) Reduce buffer weight until feed issues go away with the weakest ammo, be slightly overgassed on good ammo.
D) Just never shoot weak ammo (this is not an option to me, a gun should work with anything you throw at it).
So what is wrong with just going with C, a light buffer? If the light buffer ends up bringing bolt velocity back into spec, won't I just have a lighter recoiling rifle than if I upped the gas?
I'm guessing you don't want a weaker buffer spring because you need the spring to keep velocity high enough on the forward stroke to strip a round off.
As I understand it, there is an "ideal" cyclic rate, which is to say there is an ideal bolt velocity. If the bolt velocity is too low, you can see things like failure to strip off a new round, failure to lock open, or even stove pipes. Things that could contribute to this could be weak ammo not generating enough gas pressure, gas port drilled too small, gas system length not correct for application (dwell time too short), or BCG/Buffer too heavy.
So from a physics perspective, I see two major groups of components. All the pressure generating aspects (strength of ammo, gas system sizing/length) which determine how much force is applied to the BCG, and then there is the weight + spring rate of the BCG+Buffer+Buffer_Spring. If you change something to generate more gas/pressure, more force is applied to the BCG and your bolt velocity goes up. If you reduce weight in the BCG+Buffer, or reduce spring rate, bolt velocity should go up. And visa versa.
Why would it be better to change the gas system versus changing the reciprocating weight? Assuming either change results in obtaining the ideal bolt velocity.
I am working on 10.5" barrel, carbine length gas system, with an M16 bolt carrier, in 7.62x39. The primary goal of this build was being able to train with cheap steel ammo (Wolf 122g and the like). I have worked my way through feed ramp issues, and magazine issues. I am now confident that I have a (low) bolt velocity issue. I originally built it with an H2 buffer, and it was a complete train wreck. It wouldn't lock the bolt back on an empty mag with any ammo. Once I went to a standard weight buffer, it would lock back on silver bear ammo, but not reliably on wolf. The silver bear ammo fed quite reliably, but with wolf, I would get frequent failure to feed, where there was no jam, just no round in the chamber. Rack it and it was back in action. I tried modifying a standard carbine buffer by replacing one of the standard steel weights with aluminum. It ran a little bit better on the wolf ammo, but still has an occasional failure to feed which appears to be due to short stroking.
So it looks like my options are:
A) Open up the gas port to get more gas flowing, doing it perfectly.
B) Open up the gas port to get more gas flowing, overshoot, then have to add an adjustable gas block and or a heavier buffer
C) Reduce buffer weight until feed issues go away with the weakest ammo, be slightly overgassed on good ammo.
D) Just never shoot weak ammo (this is not an option to me, a gun should work with anything you throw at it).
So what is wrong with just going with C, a light buffer? If the light buffer ends up bringing bolt velocity back into spec, won't I just have a lighter recoiling rifle than if I upped the gas?
I'm guessing you don't want a weaker buffer spring because you need the spring to keep velocity high enough on the forward stroke to strip a round off.
