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AR vibration question


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Hello Everyone,

Thanks for reading. I look forward to your comments and ideas.

I have a S&W M&P15 Sport that is "factory stock" except for the following modifications:

  • Magpul ACS stock
  • Magpul MOE+ grip
  • Magpul MOE Hand Guards (carbine length)

So, my modifications are mostly ergonomic and cosmetic. I haven't done anything to the trigger, buffer, barrel, gas block, sights, etc. No compensator, just the A2 birdcage as it came from the factory.

Yesterday was my second shooting experience with this rifle. However, it was the first since I added all the Magpul furniture. While shooting, I noticed the rifle vibrated on each shot. By that, I mean that it resonated like a metal beam struck with an impulsive force. Like a bell ringing for a brief moment. Sorry, I'm a new shooter but a long standing Aerospace Engineer. This is the language I know. I hope that translates to you the reader. My perception of the vibration was more than what I recall before I made the stock, grip, and hand guard changes. The ACS is very "tight" without play. Moves smoothly from position to position but then locks into place nicely. The Factory stock had more play in it. The entire ensemble seems tighter put together than before.

Am I perceiving barrel vibration transmitted through the entire rifle? I see the barrel is NOT free-floated from the hand guard (it's a $500 rifle for goodness sake) which makes me think I'm picking up more barrel vibration than a free-floated model. Or could this be something else entirely?

I watched a few minutes of video from a 3-gun match shot behind the competitors (3 Gun Nation from WV). I think I see some of the same mechanics in their rifles (Horner, Butler, et al), but maybe quantitatively less of it.

1) Is this normal?

2) If I find it objectionable, is there a configuration change I could make to reduce it?

Thanks again for your feedback.

-- Mike

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That is pretty typical out of AR-15s, some more noticeable than others. Try a JP Rifles tuned buffer spring, it does seem to help some. I tried a small plastic disk that snaps into the end of the buffer spring that Brownells sells call a "Twang Buster" but it didn't seem to help too much. For awhile I ran a hydraulic buffer in a gun and it totally eliminated it. I have since bought a JP rifle and never noticed it again.

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The noise is coming from the buffer spring as it compresses and expands back as the bolt closes. Like they said above, the JP spring will reduce it, and if you use a little white lithium on the JP spring it will be gone.

JP spring, white lithium....noted for future reference!

To clarify:

Noise isn't the issue. It's not an acoustical thing. It's a bulk mechanical observation. I see and feel the whole rifle move. Come to think of it, I hear the buffer spring less compared to before. Yeah, now that you mention it, I wasn't aware of the buffer spring noise this session like I was the first time. And I was expecting to hear it. Surely, it was still present to some extent, but the bulk rifle vibration captured my attention in this range session.

Anyway, I can't tell you how much I appreciate all the responses! I'll do a deeper cleaning and lube work on the rifle today to make sure I get the buffer tube lubricated properly. It's great to learn from more experienced people in this fantastic forum!

Thanks for guiding the FNG.

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