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Posted: 10/11/2010 1:44:01 AM EDT
| Can someone please school me on the exact function of buffers and what different weights do differently. I understand the difference between the buffers, but I do not understand how they make a rifle run differently. Thanks for the help. |
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IIRC, a heavier buffer will keep the bolt locked for a longer period of time allowing pressures to drop more and allow easier extraction. They also increase reciprocating mass, slowing down the cycling of the gun. This reduced speed can control how fast the gun fires in full-auto. It can also affect perceived recoil.
For blowback operated ARs such as 9mm units, the heavy 9mm buffer is necessary to keep the bolt closed until pressures drop to safe levels. For most 16" users, a standard carbine or H1 buffer is fine. |
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Like strat81 said.
I'll add that heavier buffers are specifically better for certain barrel/gas system configurations; carbines with VERY short barrels, (i.e. 10.5: SBR's) or a lot of barrel length beyond the gas port, (i.e. 16" with CAR gas length.) do better with heavier buffers. From what i understand: A 14.5" barrel with CAR gas length (i.e. the military's M-4's) works best with an H2 buffer. A 10.5" CAR, 11.5" CAR, or 16" CAR works best with an H3 buffer. A 16" MID works best with an H1 buffer. A 20" RIFLE works well with pretty much ANY buffer. When using a suppressor, usually the heaviest buffer you can get works best. As a general rule, most would agree it's best to use the heaviest buffer that your rifle can use, and still cycle the weakest ammo you intend to shoot. The "standard carbine" ~3.0oz. buffer is hardly good for ANY configuration at all. Perceived recoil, as well as muzzle climb are typically reduced a little with heavier buffers, but more importantly, make the cyclic rate slower, which reduces wear, and especially prolongs bolt lifespan. Ever heard of how in a full-auto M-4, before they switched to using H2 buffers, and bolts made of a better steel, (carpenter 158 vs. 8620) that bolts would break after ~1500 rounds? that was because of a higher cyclic rate/bolt velocity, and unlocking/extraction being too abrupt, and too soon, so the bolts were subject to a lot more stress. Since the BC and buffer both move back during unlocking, a heavier buffer will slow unlocking, and thus delay extraction, meaning chamber pressure is lower when the case is extracted, which makes it easier for the case to be extracted. Hope this helps. |
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Lets back it up a bit.
The bolt is held closed/worked open in a gas gun by the math of the buffer and B/C mass/weight, the recoil spring tension, and the amount of gas pressure to force the above back. In regards too all this above math, the deciding factor for the correct tune is to allow the bore residual pressure to drop to an amount that the spent case is pressure bound to the chamber walls to be smoothly extracted. To much residual pressure bonding of the spent case to the chamber walls at cycle, and too much rearward force if lost trying to pull the bound spent case out, which is called over function and results in the rifle shot stroking. To little residual pressure in the bore, and although the case can be extracted cleanly since it is no longer pressure bound, but there is not enough pressure going to gas system to cycle the action correctly (again, short stroking will too much pressure lost out the muzzle before the action stated to stroke). Now the above math is fairly simple, but the the deviations in the math are what kind of pressures different ammo's are generating at the gas port due to how they are loaded (working pressures), what type of powder is being used (since slower burning powders will move the peak burn pressure closer to the gas port, and even chamber condition since a rougher/tighter chamber will not release a spent case as cleanly as a smooth standard sized one. Now since Buffer weight is the easiest and quickest way to change the math without modifying something, the weight range for carbine buffers range from the standard of 2.9oz, all the way up to around 10oz when you get into the custom buffers. In most carbine rigs running standard ammo and have mil-spec chambers, the 2.9 buffer is all that is needed. In the Colt M-4, the rig was designed to run heaver bullet ammo with slower burning powder, and since this powder would increase pressure at the port, the H buffer was designed to put the cycle back into check. Now we jump from the military market, and to the civilian market. Here, chamber conditions and gas port sizes do vary, and when a chamber is tighter or rougher, then the residual pressure in the bore needs to be dropped down farther for a clean spent case extraction, and often you will see a heaver buffer suggested when over function problems are reliant. For the most part, this swap in buffer is more of a band aid than correcting the problem itself, but since the buffer is cheaper and can be done by the end user, suggested instead. So bottom line, In a standard full stock rifle, the standard buffer is all that is needed. In a Carbine unit, again, the standard carbine buffer is all that is needed for standard ball ammo. If and when you do step the ammo up to the Mk 262 range with it's slower burning powder, then stepping into a H buffer will slow the unlock back down (due to the slower powder creating higher action dwell pressures) to put the action back into check. As for aftermarket buffers the weight differences for full auto rigs, these are used to control the fire rate of the weapon, and even to the point of controlling bolt lock up to prevent carrier bounce at the hammer comes back down. Simply, this is a whole different ball game than the semi rigs, and controlling something in the full auto rigs that is of no concern to the semi auto rigs. |
| Thanks for all the info. I am running a BCM 14.5" middy with a standard carbine buffer. BCM made a point of recommending the H-buffer, but they also recommend using military grade ammo. I wanted to use some cheaper ammo for training, and was unsure how the buffer would effect this. I currently have a standard buffer, and, if I am understanding you correctly, the standard buffer is worse at firing low power ammo. |
With the 14.5 middie setup shooting quality ammo is more important than with other setups because of the shorter dwell time .... with the middie 14.5 you moved the gas port closer to the end of the barrel and then cut off an inch and half .... changes the timing of the gas system and it's not going to function reliable with low pressure ammo.
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| So, with my 14.5" middy, am I better off using a lighter buffer to compensate for decrease in dwell time? My thinking is that if a heavier buffer allows more time for pressures to drop, I would want to keep my pressure up a bit because of the shorter dwell time. Am I completely off base? Thanks again for the help. |
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Quoted:
So, with my 14.5" middy, am I better off using a lighter buffer to compensate for decrease in dwell time? My thinking is that if a heavier buffer allows more time for pressures to drop, I would want to keep my pressure up a bit because of the shorter dwell time. Am I completely off base? Thanks again for the help. Perhaps, a 14.5" mid-length is probably just about the only setup that the standard ~3.0oz. carbine buffer may be suited for. |
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Quoted:
Thanks for all the info. I am running a BCM 14.5" middy with a standard carbine buffer. BCM made a point of recommending the H-buffer, but they also recommend using military grade ammo. I wanted to use some cheaper ammo for training, and was unsure how the buffer would effect this. I currently have a standard buffer, and, if I am understanding you correctly, the standard buffer is worse at firing low power ammo. No, you would want to go to a heaver buffer if the working pressure is too high in the gas system, which would slow down the unlock to resolve over function. With under power ammo, the lighter the buffer and recoil spring tension, the better off you would be to get the rig to cycle correctly. |
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