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View Full Version : Suppressing AR-15s, basic questions


MagnumWill
October 2, 2011, 11:33 PM
OK, so now my mind has wandered to my NEW future project. I want to get a decent AR-15 (leaning towards a Colt), and wanted to do some brain-picking. Said AR-15 I want would mostly be a carbine length, ACOG-style scope, and suppressed. Since I'm new to suppressors (and AR-15's, for that matter), I wanted to ask if there certain AR-15s that naturally do well with suppressors, whether barrel length plays a large part in suppressor function, noise, reliability, etc. Also, if I'm going to the length of putting a suppressor on it, I'll SBR it as well. Any negative effects to that as well? Thanks!

m.p.driver
October 3, 2011, 03:02 AM
.300 Whisper

Crosshair
October 3, 2011, 07:30 AM
Barrel length most certainly does play a role in how effective a suppressor is. The longer the barrel the more effective the suppressor will be. (Though at some point the increases become marginal.)

As for an SBR, be aware that shortening the barrel too much voids the warranty on the can. IIRC AAC for example will only warranty the can on barrels down to 10.5". Virtually every manufacturer has a minimum barrel length. The problem is that the short barrels tend to sandblast the blast baffle with unburnt powder.

The suppressor will indeed affect reliability. They increase the back-pressure and will tend to increase the cyclic rate. If your specific gun is under-gassed a can will help increase the gas flow, if the gun is over-gassed a can will aggravate the problems that come with that.

Bartholomew Roberts
October 4, 2011, 09:10 AM
Do you plan to use the can almost all the time or only occasionally? Using it only occasionally on a short-barreled rifle will mean you need to make some decisions before you buy the SBR on whether you want to optimize it for unsuppressed or suppressed use. The shorter your barrel, the more narrow your "operating window" is and the more dramatic effect putting a suppresor on the barrel will have on that window.

In general an AR suppressor makes the gun quieter by suppressing the muzzle crack; but you still have the mini-supersonic shock wave that accompanies the bullet. Because a longer barrel burns the powder more thoroughly and gives more volume for combustion gases, it will generally be slightly quieter than a shorter barrel with the same suppressor.

The flip side to a suppressor is it adds weight, length and heat. The suppressor will heat up much, much faster than the barrel. Nomex gloves would probably be a worthwhile investment for a sem-auto SBR and suppressor combo.

My review of my Ops Inc. 16th model suppressor on an AR:
http://thefiringline.com/forums/showthread.php?t=272528&highlight=ops+inc

rjrivero
October 4, 2011, 11:43 AM
.300 Whisper

For subsonic plinking, the .300 BLACKOUT has been SAMMI approved. I would go that way before going with the .300 Wisper or .300/.221

But, Like Mr. Roberts, I have an Ops Inc 16th that does a fine job on my .223/5.56 AR's. I like to have a gas buster to keep the gas out of my face for high round count stages and such.

MagnumWill
October 5, 2011, 09:19 PM
I assumed that a shorter barrel was going to be a little more abusive on the can, but not to the extent of losing the warranty. I would use it all the time, if anything I may integrally supress it (so I can bypass the SBR thing). I have seen that the Masada (BM ACR) has an adjustable gas port- are there any normal AR's that do this?

Crosshair
October 6, 2011, 07:12 AM
I assumed that a shorter barrel was going to be a little more abusive on the can, but not to the extent of losing the warranty.
How short are you thinking of going?

rjrivero
October 6, 2011, 08:41 AM
I assumed that a shorter barrel was going to be a little more abusive on the can, but not to the extent of losing the warranty. I would use it all the time, if anything I may integrally supress it (so I can bypass the SBR thing). I have seen that the Masada (BM ACR) has an adjustable gas port- are there any normal AR's that do this?

It will, to a certain degree. There will be some blast erosion to the blast baffle. Most cans have stainless blast baffles for this reason in .223.

A lot of manufacturers will only warranty to a certain barrel length because of this.

However, Zak Smith makes one specifically for the short barrel full autos. Down to 7" barrels (Which I believe is the shortest you can go with an AR)

http://thunderbeastarms.com/products/223a

Any "normal" AR can have an adjustable gas block. PRI makes them, among others. You just port out your gas port to .750 and use the screw on the side of the gas block to optimize your gas port setting.

http://www.midwayusa.com/viewproduct/?productnumber=775354