BCM 11.5 gas issue?

[Bantam1]

I have been trying to get a friends BCM 11.5 to calm down for lack of a better term. It is what I thought to be way over-gassed. I installed an adjustable gas block, fresh carbine spring, Sprinco blue spring, carbine, H, H2 and H3 buffers and the buffer still smacks the receiver extension during recoil. It is one of their assembled uppers with the standard profile BFH barrel and BCG. No matter what I have tried the thing just seems to have a "harsh" recoil for a 5.56 AR platform. It feels like an old blowback Colt 9mm carbine I shot years ago instead of a regular DI AR.

I checked the carrier travel to make sure its not hitting the receiver. No issue there either. Tried different types of ammo including some lighter handloads I made for it. The lighter loads helped but he wants to run 556 since that is what he uses in his other rifles.

I was able to get the ejection pattern to change from about 1:00-2:00/2:30 with the buffer/spring change and the gas adjusted to just barely reliable. I have assembled several uppers for myself and friends and all of them run great or need some slight tuning, but this one is just angry for some reason.

I have not tried an A5 extension and buffer yet. I was hoping someone here might have been through an issue like this and have some insight. Or maybe point me in the right direction as to what I could check that I might have missed.

 

[DeathBeforeDismount]

These guns are built, like most duty AR's to run when they are dirty and adverse. This means a larger gas port to ensure that it will run when the gun is caked up and has enough energy to cycle.

What stock are you using? I can't imagine ANY .223/5.56 having "harsh" recoil but stock choice is going to make the biggest difference in how it feels. You probably did not install the adjustable gas block correctly or have a defective one. They are all shit in the long run and why I do not use them or recommend them for anything but gamer guns.

If you really are adamant about controlling the gas and keeping this reliable, get a bootleg carrier and adjust the gas down. Put the non adjustable FSB or gas block back on and make sure its seated correctly.

 

[longshot2000]

Pretty much what @DeathBeforeDismount said. While I like a lot of BCM products for being above average duty grade rifles and components, I am not fond of their barrels. But, most likely, the gas port is oversized. At 10.3" that makes a lot of difference. At 11.5", a carbine barrel tends to be a lot more forgiving, and very adjustable with buffers. I am not sure if you are sensitive to the recoil or if there is a problem. You said you used various buffers and an adjustable gas block and Sprinco springs. Not much else you can try. Sure, you can try Vltor, but you should be able to tame the beast. You might try a Geissele spring, but most armorers will tell you that Sprinco is better. You never know, the braided wire tends to be softer and quieter.

 

[msgriff]

Which AGB, and were you able to adjust it down so the action would not cycle? If so, how many clicks/rotations did you go beyond failure to cycle?

 

[Evintos]

I have been trying to get a friends BCM 11.5 to calm down for lack of a better term. It is what I thought to be way over-gassed. I installed an adjustable gas block, fresh carbine spring, Sprinco blue spring, carbine, H, H2 and H3 buffers and the buffer still smacks the receiver extension during recoil. It is one of their assembled uppers with the standard profile BFH barrel and BCG. No matter what I have tried the thing just seems to have a "harsh" recoil for a 5.56 AR platform. It feels like an old blowback Colt 9mm carbine I shot years ago instead of a regular DI AR.

I checked the carrier travel to make sure its not hitting the receiver. No issue there either. Tried different types of ammo including some lighter handloads I made for it. The lighter loads helped but he wants to run 556 since that is what he uses in his other rifles.

I was able to get the ejection pattern to change from about 1:00-2:00/2:30 with the buffer/spring change and the gas adjusted to just barely reliable. I have assembled several uppers for myself and friends and all of them run great or need some slight tuning, but this one is just angry for some reason.

I have not tried an A5 extension and buffer yet. I was hoping someone here might have been through an issue like this and have some insight. Or maybe point me in the right direction as to what I could check that I might have missed.

The A5 will smooth out that impulse especially if combined with the adjustable gas block, however, if you want to decrease that impulse feel to a bare minimum, you go low mass.

If you had a JP SCS, you could even go as far as shorten the rear bumper to increase the stroke length. You could also do it with the buffer body. Much more involved process though.

The other potential option is simply unscrew the receiver extension by 1 turn (as long as it still retains the detent).

If you're messing with stroke length though, take care to ensure the gas key of the BCG isn't hitting the lower receiver at the end of its travel.

 

[Bantam1]

Trust me I know what you guys are saying. It's not harsh in like it has heavy recoil of something with a larger caliber. It's not my upper, just trying to help a friend out with his. None of my rifles have this issue as none of the buffers will bottom out on the extension under the cycle of operation. I'm not recoil sensitive. But having owned and shot a lot of AR pattern rifles in many different calibers this one just feels wrong. Does that make sense? I have had barrels that were a little over gassed and a gas block or buffer took care of that. This one isn't responding to any of that.

The stocks were CTR and BCM.

The buffer is hitting the back of the receiver extension based on how it feels to me. This is with the gas turned down and different buffer weights and a heavier spring. I tried the gas block for him since I had a spare. I could adjust it not to cycle completely, so I literally have it one click open past bolt locking on empty mag to eliminate as much gas as possible just to see what was going on. I typically go at least two clicks past that point to ensure it runs when a little colder out, or dirtier.

I just don't think it should be that difficult to tune and stop it from happening. That's why I'm asking if anyone else has had one like this. I haven't had him order a Red spring from Springco or try one of my A5 lowers with it.

 

[BravoSector1]

The upper is overgassed to ensure function and reliability. JP low mass BCG and or JP Silent Capture Spring system may help.

 

[the monk]

Had the same issue. The main fix is a Black River Tactical EZtune gas tube - https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Configurable-Carbine-p103167251. Fill out the form and they will tell you what size you need. His gas tube last for at least 5k rounds.

Second, as stated above, a A5 system with a A5H2 will also even things out. I run both on my 11.5 BCM and it's my go to.

 

[TonyTheTiger]

I have been trying to get a friends BCM 11.5 to calm down for lack of a better term. It is what I thought to be way over-gassed. I installed an adjustable gas block, fresh carbine spring, Sprinco blue spring, carbine, H, H2 and H3 buffers and the buffer still smacks the receiver extension during recoil. It is one of their assembled uppers with the standard profile BFH barrel and BCG. No matter what I have tried the thing just seems to have a "harsh" recoil for a 5.56 AR platform. It feels like an old blowback Colt 9mm carbine I shot years ago instead of a regular DI AR.

You just described how I feel about all carbine gassed guns. Yeah, the recoil is not excessive, but you can tune all day and still something about the recoil impulse makes me think parts are going to be broken soon.

 

[JS8588]

Tubbs Flatwire buffer spring and throw one of these on whichever buffer you land on. Looks goofy, but it makes a difference in the way the recoil impulse feels. https://jonesarms.com/product/eab/

In fact, on that last part, I have an extra in my office somewhere. If you'd like it, PM me and I'll see if I can dig it out on my next day off.

 

[B4forever]

+1 for the BRT gas tube. Run that in a fixed gas block, Springco blue, and a H2 or 3 buffer.

 

[Bantam1]

Thanks everyone. I have an A5 ready to roll for another rifle I am going to build in the future. I'll give that a try first to see if it works for him. If it does I'll let him keep it and have him buy me a replacement.

 

[Pappasniper]

I run A5 buffers on just about everything. But having an adjustable gas block and still having issues is just bizarre. Wildly bizarre. I would say BRT tube ( big fan) but you already have an adjustable gas block so that makes no sense. Maybe like B4forever said, remove that AGB and try a BRT tube. It will be interesting to see what gives here.

PB

 

[tucaz]

i had a similar issue a 10.5 FN barrel with a .076 port and was trying to get it functioning with an AAC SCAR-SD suppressor....nothing worked. sprincos, H3 buffer, A5's, adj gas block. it was ok with 223 pressure but not 556 full pressure. it would cycle too fast and catch the next round half way up the case. in fact the sprinco red made the problem worse and i can only guess it was sending the BGC home faster.

a centurion 11.5 with .069 port is on order now. i bought one of their 12.5's with .064 a few weeks back and its been stellar.

 

[tucaz]

I run A5 buffers on just about everything. But having an adjustable gas block and still having issues is just bizarre. Wildly bizarre. I would say BRT tube ( big fan) but you already have an adjustable gas block so that makes no sense. Maybe like B4forever said, remove that AGB and try a BRT tube. It will be interesting to see what gives here.

PB

i never heard of the tubes, thanks for dropping that. thats why i love this place for tech stuff!

 

[Pappasniper]

Yea check them out. They are a game changer and many people on here use them as well. I just put one on this week on a 16 inch middy with a suppressor and it shoots like a dream. I probably have 5 or more guns with his tubes. You can quit chasing springs and buffers and BCG's. Even though I run an A5 buffer in all buy guns, I still use his tubes so to each his own.

Good luck in the Dirty T, my boys went to school there so I am familiar.

PB