Suppressed SBR in the works - 11.5 or 12.5?

[Rodman24]

The last time I bought a stripped upper & lower, I intended to build an SBR. I ended up building a precision rig. Go figure.

I’m very satisfied with the precision rig, but the SBR hunger is back.

Keep in mind that I don’t plan on getting rid of any of my ARs, so this will mostly be for fun at the range and home defense. It will be wearing a can most of the time.


Earlier today I purchased an AAC M4-2000, and I sent off the Form 1 for my Daniel Defense lower (which is currently paired with a 16” upper). So I’ve got a while to wait before the stamps comes back.

I already have a DD upper receiver, BCG and charging handle with PRI big latch. I also have the 7” Omega X rail and FSB (from my 16’s original configuration). So all I need now is a barrel!

I know that 10.5” barrels can be really hard on a can, and the loss of velocity is also significant. So I’ve ruled that one out. But since I want the overall length to be as short as possible, I’ve pretty much decided on an 11.5” barrel (suppressor adds 5.1”). Does anyone feel really strongly about the 12.5” instead of the 11.5”? As best I can tell, the velocity losses aren’t that significant when moving from 12.5” to 11.5” (not like the 11.5” to 10.5” loss). Will that extra inch really cost me? Just keep in mind that I do have rifles for medium and longer ranges.

Also, since this will be wearing a can and since I’m a lefty, just how much gas will end up in my face? I can always convert it to a piston, but I don’t want to do that until I’m convinced it’s unbearable.

Just looking for some sagely advice.

[todd.k]

The velocity to barrel length is a curve but it's not that extreme so thinking that 11.5" to 12.5" is going to be more of a gain that 10.5" to 11.5" is a bit of a stretch.

For HD the shortest reliable setup is likely to be the best choice and that is 10.5". 5.56 ammo that performs well from a 10" to any reasonable HD range is available and is what you should run if you go with an 11.5" or 12.5".
If you want to shoot it a bunch at the range 12.5" would be easier on your silencer than the 11.5".

[Rodman24]

Thanks for the comments.

[markm]

I agree. I don't run my silencer on anything shorter than 14.5 for that reason.

As far as the lefty situation.... you will be sucking gas.... but don't go with that piston trash. It creates more problems than it solves... and gas is still going to come out of the ejection port anyway.

[Stickman]

As far as the lefty situation.... you will be sucking gas....


Until someone gets that gas in the face and their eyes close up involuntarily, its a hard concept to grasp. Once they have it happen, its an eye opening experience (no pun intended).

[TehLlama]

For the OAL issue I really wish that Surefire or AAC would modify their SPR/FA reflex cans to have a short baffle stack version (I'm thinking an SF 556FA with the Micro baffle stack or a shortened SPR/M4 with a 6" can OAL), so that there were better fast attach reflex options for a suppresse SBR application. I chose to get an OPS 14th as well as an OPS M4S for these applications - I'm really happy with the overall length, but to get much can life on my 11" unit, I'm running it with a muzzle brake (dedicated suppressed with a smaller gas port).

I figure that after the cost of enough rounds to really burn out a suppressor to where it's no longer usable, that's at least the suppressor's pre-tax value worth of manufactured ammunition anyway, so if OAL and terminal performance are both what you want, then the 11.5" is probably plenty good of a compromise with the M4-2k. IIRC, Noveske even makes that length (or did), in addition to all the other options out there in that length.

I'd try the RTV Silicone trick (even on the PRI M84) to see if that helps, but you're still going to be at the mercy of soot puffs coming out.

[Rodman24]

I'd try the RTV Silicone trick (even on the PRI M84) to see if that helps, but you're still going to be at the mercy of soot puffs coming out.

Not familiar with the RTV Silicone trick. Can you explain?

[Quib]

Not familiar with the RTV Silicone trick. Can you explain?


http://www.coloradoshooting.org/gas%20buster.htm

[lmtrocks]

<------ Southpaw. When running my 10.5" 762x39 and 12" 6.8 uppers suppressed the gas in my face is just makes me a little aware of it's presence in front of my face but it's not at all obnoxious.