Posted: 7/11/2016 4:48:37 PM EDT
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The question is whether a change in the weight of the buffer in an AR15 type rifle will have any effect on the point of impact of the bullet downrange?
I don't know but share limited anecdotal experience with this over the past weekend. I have a match grade barrel that should be overgassed based on port diameter and location. It is in a 16" carbine with a carbine buffer. It has not seemed to be slamming the bolt or working too "hard" but I decided to experiment with a heavier buffer. I bought two tungsten buffer weights from Geissele and installed them in a spare carbine buffer with one steel weight, thereby creating an H-2 buffer. In this test, I fired ten shots (two five shot groups) of precision match ammo with the standard carbine buffer (I am doing some load development). I noted the point of impact. As a curiosity, I then replaced the buffer with the H-2 and repeated the test with ten more rounds (again, two five shot groups) from the very same batch of ammo and rifle. All else was identical. The point of impact did not shift. I mean, these are 1/2" groups at 100 yards, so any change would be apparent. I'm not discussing a change in group size. I would not expect that. But I did expect that the center of the group would change. My thinking is that with the slower moving bolt, the recoil impulse might have an effect on the position of the barrel at the time the bullet left the muzzle, or at least have a secondary effect due to altered recoil.. I have not done the scientific study to determine whether the bullet has already left the bore at the time the bolt begins to move, but my conclusion is that perhaps it has, based on this admittedly limited experience. No doubt, someone here has actually studied this from a data perspective. Since I did not change port diameter or port location but rather slowed the bolt down, this may mean that the timing of the bullet leaving the barrel did not change and thus, impact did not change. The rifle had no FTF or FTE with either buffer. Subjectively, the rifle seemed to shoot a bit "softer" (only very slight) with the heavier buffer in place, but ejection pattern did not change very much. That is a poor indicator, anyway, except perhaps relatively. In this case it moved from 2 to 3 o'clock on the one hand with the carbine buffer, to 3 to 4 o'clock with the H-2 on the other hand.. FYI, these loads were match target ammo at .223 chamber pressure, not full power 5.56. If there was to be a cycling problem with the heavier buffer, I would have expected to see it. As stated above, there were no FTF or FTE and point of impact did not change. This was an unexpected finding. I had completed the load development and had some extra ammo. I wanted to see if the H-2 buffer would cycle it. That was the only reason to shoot the last two five shot groups - function testing of the ammo and buffer together. Thoughts? Just curious. |
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I'm pretty sure by the time the bolt is in full motion the bullet is long gone. But that's my not so scientifical observations from slow mo on YouTube. Also the bolt and buffer moves straight back to the rear. So ideally if you have a good shooting positionot, the rifle should not do anything other than move straight back. Again this is my unscientifical observations.
Scott |
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I agree that the buffer shouldn't affect single shot accuracy. This is a precision forum.
However, buffer springs and buffers affect cycling rate, recoil and return of sight picture for quicker follow on shots. Most likely that led the Marines to select Vltor's A5 buffer system. |
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