BCM 11.5/LMT Enhanced/A5/Suppressed Gas Question

[JustDSM]

Guess I'll just ask directly this time..

Background: I'm building a 11.5" SBR that'll serve as my general purpose carbine, home defense rifle, plinker, training weapon, show and tell piece, and whatever else you can think of. It'll be shooting at least 75% of the time suppressed through a AAC M4-2000 can generally fed 5.56 spec ammo but want .223 capability if the need arises.

Pertinent rifle parts:
AAC Blackout
AAC M4-2000 Can
BCM BFH 11.5" Barrel
*LMT Enhanced BC*
*LMT Std. Bolt*
VLTOR A5 System


It's nothing new around here that the BCM BFH, regardless of length are one of the go-to barrels. The VLTOR A5 system seems to get the universal nod as well. After reading about all I could regarding similar setups and gas system issues/ect. you'd be hard pressed to miss Grant's SBR/Suppressed thread. Without disclosure of gas port dimensions of his N4 barrel I am a little curious how my BFH's (11.5") gas port dimensions compare.. But I don't figure that'll be disclosed.. So rather than a quantitative comparison perhaps we can look at this from a qualitative assessment.

I suspect the BCM gas port dimensions are a bit larger than the N4 barrel Grant spec'd in his case. All things being equal this would have the BCM rifle being slightly more gassed than the custom N4. IIRC Grants rifle doesn't lock back when shooting with the can detached. And from my understanding thats with the utilization of the standard carbine receiver extension and buffers (of various weights).

What I'm hoping to do is stir up some discussion on "obtainium" barrels vs. custom spec'd "unobtainium" barrels and building a reliable and dependable SBR that functions both suppressed and unsurpassed. From what I've been able to dig up, I haven't found much of any chatter on this type of setup. If I've somehow overlooked the obvious, please advise and point me/us in the right direction as I'm not likely alone in this quest. Or certainly won't be the last..

So.. In summary: Those of you with experience or direct knowledge of the BCM BFH in SBR configuration (preferably 11.5") Is the LMT Enhanced carrier worth it to make a reliable carbine? Or have you had success with a standard BCG with similar conditions to the intended use/treatments that my rifle is to be exposed?

[markm]

Standard Carrier will run fine. The Enhanced carrier may help a little. If you're running a lo profile gas block, you can always get a syrac adjustable and tune the gun to exactly where you want it.

[Iraqgunz]

My 11.5" and 12.5" are almost identical to your specs. Except that I use BCM bolts in my carrier groups. I use the A5 with the green Sprinco spring and the A5H4 buffers.

Your gas port size is around .076 and it will run just fine. I have run PPU 5.56, PMC Bronze Line, M193, M855, Hornady Steel TAP 55/75gr., IMI M193/M855, Federal Independence 5.56, and religious deity knows what else. Malfunction free for over 19K rounds with the exception of a few ammo related problems.

[JustDSM]

Standard Carrier will run fine. The Enhanced carrier may help a little. If you're running a lo profile gas block, you can always get a syrac adjustable and tune the gun to exactly where you want it.

My 11.5" and 12.5" are almost identical to your specs. Except that I use BCM bolts in my carrier groups. I use the A5 with the green Sprinco spring and the A5H4 buffers.

Your gas port size is around .076 and it will run just fine. I have run PPU 5.56, PMC Bronze Line, M193, M855, Hornady Steel TAP 55/75gr., IMI M193/M855, Federal Independence 5.56, and religious deity knows what else. Malfunction free for over 19K rounds with the exception of a few ammo related problems.

I'm happy to hear this combo gets it done. Thanks you both for sharing your thoughts and experiences. I had two further questions for IG; I don't wan't to assume but it sounds like you're using the LMT E carrier - is that correct? Lastly, can you share why/what drove you to end up with the H4 buffer in the A5 system?

[markm]

I read someone's comment here that the E carrier allowed them to run a heavier buffer. I'd like to try one in my suppressed SBR just to see what, if any, difference I could detect.

[Iraqgunz]

Yes, I use the LMT E-carrier. I ended up with it because it actually works. I have started with the A5H3 and I suspected it would work with the A5H4. So I tested it to confirm that it would work.

I'm happy to hear this combo gets it done. Thanks you both for sharing your thoughts and experiences. I had two further questions for IG; I don't wan't to assume but it sounds like you're using the LMT E carrier - is that correct? Lastly, can you share why/what drove you to end up with the H4 buffer in the A5 system?

[Sparky5019]

Ok, this brings me to ask...

What would the A5 system add to a 10.3"/11.5" gun that is running a Syrac?

[TehLlama]

Ok, this brings me to ask...

What would the A5 system add to a 10.3"/11.5" gun that is running a Syrac?

Still nets a wider operating envelope of gas pressure impulses - with enough various springs/buffers, or just with adjusting the effective gas port size (Syrac or other adjustable gas block) any system can run smoothly while clean with one type of ammunition, for the A5 the bigger buffer which keeps it locked a touch longer, and mostly longer spring with less variable spring force as it compresses improves the reliability when running dirty, and especially with less powerful ammunition.

[Sparky5019]

Still nets a wider operating envelope of gas pressure impulses - with enough various springs/buffers, or just with adjusting the effective gas port size (Syrac or other adjustable gas block) any system can run smoothly while clean with one type of ammunition, for the A5 the bigger buffer which keeps it locked a touch longer, and mostly longer spring with less variable spring force as it compresses improves the reliability when running dirty, and especially with less powerful ammunition.

Ok. So basically if using a Syrac AGB, there would be no major benefit given the cost. I guess what I'm saying is, if I'm able to tune down the gas (suppressed and unsuppressed) and running with a Springco blue and say an H or H2, there would be no perceptible gain with the A5. Correct?

[TehLlama]

There's still a benefit - the adjustable gas block means you can tune it from that side a fair bit, but in my experience the real gain for the A5, when comparing against other buffer systems in white space, is that they'll run across a wider RANGE of gas impulses. So, when people are going on about how much smoother the A5 is, it's not that one can't make a standard .mil type buffer setup run beautifully with something like a Sprinco Blue and H-2, it's that they can get that same level of smoothness without giving up as much ability to run at slightly lower pressure, or slightly dirtier.

It's not about making any perceptible gains at the prime configuration (go-time ammunition, cleaned, lubed, muzzle device or can desired), since that can be tuned for easily [see competition guns that can be very light, have the recoil of a mouse fart, and be conditionally reliable; they run great in one setup, and will choke outside that small performance envelope]. What the A5 offers is that if the gun is set for maximum reliability across a larger performance envelope, that it's probably more smooth in that prime configuration than an equivalent pessimistic setup with a standard or Sprinco white buffer spring and an H or H2 buffer.

What a Syrac/A5 gets you is the ability to choose the maximum input from the gas system size (reduce effective gas port size), and run relatively lighter A5 buffers (probably run the Green Sprinco on it) while basically getting minimum recoil in a prime setup (especially for suppressed applications) without giving up the ability to lock back on empty magazines across the maximum possible range. It's just that this effect is going to be reduced, the A5 does the most on oversized gas ports since it's easy to run lots of gas and an A5H4 or something to make a carbine uber-reliable, and still have decent recoil characteristics; on a double stamp setup with a smaller effective gas port, there's less gain from a more massive buffer with longer spring since there's a smaller gas volume being moved across, but in the right combinations an A5 setup can be somewhat reliable both suppressed and unsuppressed with lower backpressure cans.