View Full Version : 11.5 Suppressed SBR buffer system change to A5?
Upper - Factory BCM 11.5 ELW BFH KMR-A upper with BCM BCG and Geissele ACH. Muzzle Device is a SiCO Trifecta Mount. Optic is an Aimpoint T-2 in ADM mount with Magpul Pro BUIS and an X300V
Lower - Mega Arms Gator (SBR'ed), BCM LPK except Geissele SSA, Noveske Ambi Safey. LMT Carbine RE, Colt H3 and Blue SpringCo. BCM Gunfighter grip and stock.
Current operation - I use this weapon 95% of the time suppressed with a Saker 556K. It operates 100% but it took the H3 buffer to settle down the ejection / recoil, but it still kicks them out energetically to 1-1:30 at 6-8 feet with M193 / M855 / SOST ammo. Casing aren't dented, it just throws them forward quite a bit.
Not bad recoil (its only 5.56) but I'm wondering if the A5 setup might smooth it out a bit more.
This summer I purchased a BCM VLTOR Buffer tube, A5H2 and A5H3 Buffers, BCM and SpringCO Green rifle springs. My job sidetracked the project, because I can't stand to sideline a solid rifle for a long time - basically I need to do the mods and test them within a day or so or I put off changes until I can.
In general I hate needless change but after reading all the A5 threads, I think it could smooth out the weapon.
Any input / thoughts from the crowd?
I like the A5 and would pick it for a fresh build. But I don't think the proverbial Juice is worth the squeeze in your case. If an H3 is still banging them out at 1:30 I'd be thinking of reducing gas somehow.
This is based on your description only.... shooting the gun and getting an idea of the recoil impulse would give me a more solid opinion of what to do.
(edit: I just noticed the springco factor. I don't know what the blue does in this equation)
A5H3 and Sprinco will run all day long and 98% sure that an H4 will work as well.
I run a factory BCM 11.5 (BCM lower also) with an A5H4 and it will run un-suppressed with the weakest of ammo. No problems ever.
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Jwknutson17
12-15-17, 15:23
The H3 and blue is the best option in your case here as you are already running. The 11.5 BCM barrel I have gone away from over the years as it's gassed a little heavy. An adj gas block or insert would help you greatly. The other option is buy a smaller ported carbine barrel and have it cut down to 11.5. The Sionics 11.5 is a little better then what you have port wise, but I don't think you will be wowed by that difference. You need something in the .0625-.0650 range to make you happy for suppressed use. And still have it function with what ammo you mentioned unsuppressed. .0625 will function fine with 5.56 ammo unsuppressed with a A5H2 and Colt spring. .223 may have some issues with that port size unsuppressed.
For reference that BCM is .076 port size. Sionics RGP barrel is .071.
Jwknutson17
12-15-17, 15:26
A5H3 and Sprinco will run all day long and 98% sure that an H4 will work as well.
This is true. But I don't think he would be happy going to that A5H4 weight. Feels much more harsh from my experience.
I think fixing it from a gas stand point and setting the baseline with the A5H2 or H2 buffer is optimal. Just what I prefer.
That's how mine are set up and they run fine. SEMMV
This is true. But I don't think he would be happy going to that A5H4 weight. Feels much more harsh from my experience.
I think fixing it from a gas stand point and setting the baseline with the A5H2 or H2 buffer is optimal. Just what I prefer.
After my experience tuning a couple of suppressed 11.5" shorties and consulting with Clint of BRT, I'll share my experience and thoughts.
Tuning an AR consists of balancing gas flow, reciprocating mass and spring rate. One leg of the tuning triangle cannot be taken too far one way or the other without having a negative impact on the other two and possibly, the overall functioning of the AR.
The upper practical limit for buffers is about 5.3 oz, which means rifle buffer, A5H2 or H3 are at the upper limit for buffer weight using a standard full auto BCG. (The lower limit would be the H buffer.) Anything heavier and the reciprocating mass starts pushing the rifle around too much and requires more effort in getting the AR back on target after each shot. If a heavier buffer is needed, it's time to address something else instead.
One can only do so much with springs. Stiffer springs require more effort to to pull back on the charging handle and generally means more gas to overcome the spring, more momentum on closing and more need to control carrier bounce. If the springs are too light, it impacts the reliability of feeding.
The third leg of the triangle is gas flow. Gas flow is controlled by balancing gas port diameter and pressure. The higher the pressure, the smaller the diameter and vice versa.
Reciprocating mass and spring rate are somewhat fixed between having enough momentum to operate the AR in such a way it promotes reliable feeding but not so much that it pushes the rifle around too much or starts to batter parts. Once mass and spring rate is determined, it's time to set gas flow so that carrier speed is enough to ensure the right momentum.
What all this means is, tuning an AR is more than throwing in the heaviest buffer an AR will reliably function with. It sounds like rocket science-and it is- but fortunately, it's simple rocket science. It just requires knowledge of what the upper and lower limits are to each leg of the tuning triangle.
I took two approaches in tuning suppressed 11.5" shorties. First, I used a pistol RE which takes carbine buffers and springs. It currently uses an H2 buffer, Colt carbine spring, Colt extractor spring and SLR adjustable gas block. The gas block was tuned so that the AR would eject but not lock back on the last round, then opened one click. This provides soft recoil and reliable function. It feels as though the buffer barely touches the back of the RE. I keep it lubed by applying a couple of drops through the carrier exhaust ports. I have yet to have to open the gas block to keep it running when the fouling builds up. I will see this winter whether or not if it will need to be opened up due to cold temperatures.
Second is a suppressed Colt 6933 configured with an A5 RE, A5H2 buffer, Sprinco green spring and a .063" BRT microport. Recoil is quick without being sharp. The buffer can be felt stopping against the RE firmly, but it's a cushioned stop, not the harshness from bottoming out. Functioning is reliable and the extra fouling from running a suppressor is much reduced, another advantage to reducing gas flow rather than going with a heavier buffer.
Both shorties use direct thread Omegas with 5.56 flat caps and Federal 55 gr 5.56.
After my experiences, I realized that buffer weight choices have already been made for us. The only real choice is setting gas flow. My opinion is that the H/H2 buffers are the sweet spot for ARs with barrels between 16 and 10.5 inches. The A5 RE with the A5H2 buffer is just as good and, in my opinion, a little more forgiving. I like the A5 RE a lot and I like it even better with the Sprinco green. I have never tried the A5 with any buffer but the A5H2. After writing this, I'm curious how the A5 would do with the weight equivalent of the H/H2 buffers.
So, what does all this mean? Rhino, your AR is at a point where you need to think about tuning gas flow. You do have room to go up one buffer weight. If you do, then I'd go with the A5 and also get the benefit of running a rifle spring. Depending on the gas port diameter of your barrel, the heavier buffer may be enough but as you're running a suppressor, I don't think it will. If stepping up another buffer weight doesn't do it, then you will need to fix your gas flow.
An SLR gas block or BRT micro port along with an H or H2 buffer, quality action spring will give you a sweet shooting suppressed 11.5" AR. Or, for the slight advantage of the rifle spring, use an A5 RE.
I'd agree with the heavy H3 carbine/H4 A5 yielding too much "pop" in recoil impulse. The extra ass ache of gassing the gun down is worth it.
Pappabear and I choked down like 5 or 6 shorties (10.5/11.5 5.56mm) and shot a bunch of them on the same range trip. It's interesting how each gun has it's own impulse feel. But every one of them ran WAY better with a reduced gas port. By better I mean smoother cycling, machine like ejection patterns that pile brass up neatly one by another like an A2 rifle.
I should have also mentioned I used the LMT E-Carriers as well.
I'm interested in this as well because I just bought a new 11.5" ELW upper to run with a Sandman-K full-time. I'm starting with a H3 Super 42 just because I want to try that combination out, but I'm always on the lookout for something better. The can is still in jail so time will tell how it runs.
I should have also mentioned I used the LMT E-Carriers as well.
What has your experience tuning with the LMT E-carrier been? I used one with a 10.5" and 11.5" upper, suppressed and unsuppressed. In each case, using them with the SLR gas block, I needed to close the gas block one click more with the E-carrier compared to a standard full auto carrier. The E-carrier needed less gas.
Jwknutson17
12-15-17, 16:58
What has your experience tuning with the LMT E-carrier been? I used one with a 10.5" and 11.5" upper, suppressed and unsuppressed. In each case, using them with the SLR gas block, I needed to close the gas block one click more with the E-carrier compared to a standard full auto carrier. The E-carrier needed less gas.
I know the question is not directed to me, but thought I would share my results.
In a few chop down SBR builds I have had some weird experiences with the E carrier. In smaller gas port guns mind you. I would find that in some cases with running certain buffer weights and the e carrier I would short stroke. Putting in the auto carrier the rifle would run. Other rifles with larger more "standard" ports I would see the results you mention above. For this reason, when running smaller ports I tend to not change up much else in the system and use A5H2 and Colt springs with a FA BCG as a baseline.
I don't use adjustable gas blocks. My SBR uppers all have LMT E-Carriers, NP3 or standard bolts, and lowers have A5's with Sprinco springs. Gas ports are .076, .076, and .070 and all of them run 100% with quality ammo.
What has your experience tuning with the LMT E-carrier been? I used one with a 10.5" and 11.5" upper, suppressed and unsuppressed. In each case, using them with the SLR gas block, I needed to close the gas block one click more with the E-carrier compared to a standard full auto carrier. The E-carrier needed less gas.
Thanks for all the responses - I agree that the weapon is likely overgassed to a degree, although thankfully with the ACH / Saker-K, I never get any gas to the face with the weapon - something I had come to expect as normal with pretty much every other AR I've ever shot without an adjustable gas block (I have an older 14.5 Noveske Switchblock for reference).
So I went ahead and did the RE / Buffer swap last night, figuring it's easy to swap back.
Shot it today with both the A5H2 and A5H3 w/ Green Rifle SpringCo - ran through some M855, M193, and Wolf to run the full spectrum of ammo - 150 rounds in total with only one user induced error (failure to adequately seat the magazine. First time shooting in gloves in awhile).
Overall the A5H3 felt the best - ejection around 2 o'clock at 5 feet, with some variation for the different ammo - shot mostly rapid drills at 7 yards and from my recollection of it with an H3, it seemed smoother and easier to keep the weapon on target for 2-5 round strings.
I'm gonna keep it as is for awhile and get some more feel for the setup. I might have to build up another SBR lower to be able to do back to back comparisons with out trying to swap REs / Buffer systems at the range.
OP, I appreciate you making this thread. I am going to through the same dilemma right now. 11.5 BCM suppressed w/ an RC-2, Colt lower currently running an H3 w/ blue sprinco. I have a new A5 kit that I got a few days ago, and was debating if it would be worth it to do the swap, as my rifle operates the way you explained in your post, to the T, it’s almost funny. I have the A5H2 w/ green spring on my KAC lower w/ an LMT 10.5 upper, but haven’t had a chance to put it through its paces, yet. Nor do I have a suppressor for it, yet. Regardless, if there’s no discernible difference between my setup and the A5, I may just go ahead and do the swap, anyway. Because, one, I already have the necessary equipment. And, two, I just love tinkering with my rifles haha.
BufordTJustice
12-21-17, 16:03
A5H3 and Sprinco will run all day long and 98% sure that an H4 will work as well.
When employed with an LMT e-carrier, an A5H4 will indeed work 100%...suppressed and unsuppressed.
BufordTJustice
12-21-17, 16:06
What has your experience tuning with the LMT E-carrier been? I used one with a 10.5" and 11.5" upper, suppressed and unsuppressed. In each case, using them with the SLR gas block, I needed to close the gas block one click more with the E-carrier compared to a standard full auto carrier. The E-carrier needed less gas.
I found that with this combo under my superb Sionics 11.5" RGP barrel with SiCo SpecWar 556: Tubbs AR10 flat wire 17-7PH spring, Vltor A5H4, LMT e-carrier, and SLR Sentry 7 Ti AGB, I could run a more restrictive gas setting on the AGB with the A5H4 than I could with an -H3, -H2, -H1, or even an A5H0 by a click or two.
So, a synergy is present between those components. See my updated post in the KAC pressure reduction system thread (I necroposted) for my update.
BufordTJustice
12-21-17, 16:11
OP, I appreciate you making this thread. I am going to through the same dilemma right now. 11.5 BCM suppressed w/ an RC-2, Colt lower currently running an H3 w/ blue sprinco. I have a new A5 kit that I got a few days ago, and was debating if it would be worth it to do the swap, as my rifle operates the way you explained in your post, to the T, it’s almost funny. I have the A5H2 w/ green spring on my KAC lower w/ an LMT 10.5 upper, but haven’t had a chance to put it through its paces, yet. Nor do I have a suppressor for it, yet. Regardless, if there’s no discernible difference between my setup and the A5, I may just go ahead and do the swap, anyway. Because, one, I already have the necessary equipment. And, two, I just love tinkering with my rifles haha.
You may want to explore what I'm doing with my AR10 lower; I'm using the steel-body PWS H3 buffer (which only has two tungsten weights inside to reach the 5.6oz H3 weight). But I'm adding an additional 3rd tungsten weight to bring it to about 6.8oz. It still does not an A5 system make, but it's getting closer. The higher mass body is a decent facsimile for the biasing spring inside the A5 buffer; it increases the mass that the BCG sees while in-battery and it works to stabilize the cyclic rate. My A5-equipped AR15 carbines throw all my brass in a bucket if I stand still (I don't).
So, maybe grab an additional tungsten weight from Geissele or eBay (caveat emptor) and swap it into a PWS H3 carbine buffer? Or buy their nearly $100 "H4" carbine buffer.
For my AR10 I'm stuck because there is no way to employ a buffer longer than the std carbine buffer without going to the AR10 rifle length RE (and the shorter-than-AR15 AR10 rifle buffer).
Yep, I run that as well. I always err on the side of caution though not knowing what ammo they are using.
When employed with an LMT e-carrier, an A5H4 will indeed work 100%...suppressed and unsuppressed.
My small port sbr had some failure to lock back with the LMT e carrier, various A5 weights. I ended up with a sionics bcg, A5H1, and standard spring.
E carrier, green spring, and A5H3/A5H4 is in the bcm 11.5
BufordTJustice
12-21-17, 19:47
Yep, I run that as well. I always err on the side of caution though not knowing what ammo they are using.
Agreed. One variable changes and it really becomes a different equation at that point.
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I use the E carrier, A5, on my 11.5” BCM. With the Saker suppressor, if I’m shooting fast I often get gas in my face that blurs my vision.
I’m a left handed shooter, so I’m sure that makes it worse. It’s annoying but love the setup.
BufordTJustice
12-21-17, 19:51
My small port sbr had some failure to lock back with the LMT e carrier, various A5 weights. I ended up with a sionics bcg, A5H1, and standard spring.
E carrier, green spring, and A5H3/A5H4 is in the bcm 11.5
Well, the size of the gas port is critical. For an 11.5” with a true 5.56 NATO chamber, .070” gas port is more than big enough to function 100%.
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