A question and an issue for you AR15 knowledgeable guys

[leemozoid]

Let me discuss the issue first. I had a registered SBR lower sitting around doing nothing so I decided to put together a hog gun. I ordered a 10.5" 7.62x39 upper to use it suppressed. I already had a 16" AR15 in this cal., but it is long and unwieldy with the can on it while getting in and out of my UTV. When I went to test fire and site it in, it is doing something I have never experienced in an AR. After firing and the bolt returns to battery, there is a distinct horizontal wobble that lasts for a half second or so. You can feel it shaking on your shoulder and in you cheek. It doesn't do it every time, but most of the time. Once every few shots it just locks into battery like any normal AR solid and still. It seems like some sort of weird harmonic resonance. The lower has an A2 style fixed stock with the standard rifle buffer and tube. Possibly this has something to do with it, but I don't know why since I am not an AR expert. The upper has an adjustable gas block so I have reduced the gas to where it seems to be properly ejecting and returning to battery. You would think adjusting the gas would change any harmonics as the bolt cycle is changing speed. When it is wobbling, you can clearly hear the buffer spring boinging back and forth inside the tube. I don't know if this is the cause of the wobble or just a result from the gun shaking. This has no effect on bench accuracy punching paper, but a quick followup shot might be all over the place.

The question I have is has anyone ever seen a heavier than standard rifle buffer that would help slow down the bolt and maybe change the harmonics? I have done some searching and while lots of places have various weighted carbine buffers, no one has anything for a heavier rifle buffer.

I use a JP Rifles Silent Capture Buffer in my 9" suppressed .300 BO. Solved all issues.

JP - Buffer Springs and Silent Captured Springs

 

[GUN DOG]

Did this in my 10mm AR to slow things down filled the rifle buffer full of tungsten weights
It was throwing brass a mile

 

[Virtuaguyver]

I've owned a couple 7.62x39 before, never got them to run right. Usually mags are the issue. Always try a few different ones just to make sure.

 

[Tinytim]

Take a video and send to me. The barrel shouldn't wobble. At all. It will vibrate but not wobble. If it's wobbling, then the barrel nut is loose.

Maybe it's going too fast and you're getting bolt bounce and you just think it's wobbling.
What kind of buffer is in it?

Sounds like barrel whip

 

[ber]

Try this

 

[kingfish]

Sorry to take so long to get back to this thread. It took them a while to get the package to me. It looked like it was used for a wheel chock at the airport. Anyway I orderd the KAK heavy buffer which arrived yesterday. I installed and tested this morning. It's running like melted butter now. Brass ejection looks good. No problems with rapid fire. I think it's GTG now. Thanks all for your help.