View Full Version : Ejection port noise shooting suppressed

17 April 2011, 18:46
I picked up an AAC SPR/M4 and took it for its first outing on my 16" LaRue Stealth upper. There seems to be a fair amount of noise coming back through the ejection port, and there's quite a bit of gas blowback. Is this typical, or could my rifle be cycling too early? The upper uses a mid-length gas system, and I'm running an H2 buffer. Does an adjustable gas system help in this regard?


1 May 2011, 10:53
The back pressure and noise is absolutley normal for an AR-15 shooting suppressed. There are a couple of ways to lessen it. The first way I would recommend is to install a Noveske Switchblock. You can order a clamp on version from Noveske. It will give you the ability to "turn down" the amount of gas needed to operate your rifle while suppressed. You can also turn off the gas and keep the action from cycling. Unless I need a quick second shot I prefer to turn the gas off.
The second option would be an adjustable piston system from Adams Arms. This gives you the ability to turn down the gas for supressed semi auto fire or for the quietest shooting you can turn it off. I'm sure you're amazed at how dirty your rifle gets too. Both of these systems will lessen the amount of fouling that gets into your receiver. The problem with suppressors is they create back pressure. On semi automatics, the increased pressure escapes through the ejection port causing excessive blast. You won't experience increased back pressure or blast while shooting a suppressed bolt action rifle. The extra pressure can't exit anywhere other than the muzzle.
I solved this problem for myself by upgrading to the Adams Arms piston on one of my rifles. I also sold my LWRC M6A2 and purchased a new LWRC M6A3 with the adjustable piston. I usually shoot my suppressed M6A3 with the gas turned off. The rifle stays much cleaner and it's much quieter. I don't mind running the charging handle for each shot since it saves a lot of time cleaning later in the day. On my next build, I'm planning to use the Noveske Switchblock. Im going to use a Noveske barrel with the factory pinned version of the Switchblock as I feel the pinned version to be superior to the clamp on. The Armalite Super SASS AR-10 also uses a similar system to the switchblock. I hope this helps solve your problem and you soon find yourself having more fun shooting suppressed.

1 May 2011, 18:54
As mentioned above. Switchblock.

2 May 2011, 06:05
Thanks for the helpful replies. My LaRue upper's gas block is under the 11" rail, so installing a Switchblock on the current barrel would require a significantly shorter rail. Once funds become available, I'll look into reworking the upper with a longer barrel with a pinned Switchblock or seeing if LaRue will sell me an OBR .556 upper. The latter features an adjustable gas system that fits under the rail, which seems like a more elegant solutions.

It seems like a gunsmith should be able to pin a clamp-on switchblock.


2 May 2011, 10:44
I would throw in a heavier buffer to see how l liked the difference, and go back to shooting without any concerns.

3 May 2011, 07:38
I'm planning to try the heavier buffer and spring in the next month or two. Futzing with adjustable gas systems would come next year as part of reworking my precision AR-15 upper based on lessons learned running thousands of rounds through this one. I'm thoroughly enjoying the can in the mean time and still in the data-gathering phase of how it affects point of impact. It's way too soon to make any major changes.


9 July 2011, 15:27
Id go the swithchblock route as others stated, you will notice a definite decrease in ejection port noise with the gas off.

10 July 2011, 11:02
I'm curious if people have noticed a difference in port noise between DI and gas-piston rifles.