I’m having some trouble with my carbine and I’m in need of some help. Basically, my rifle short strokes with under powered .223 spec ammo. It won’t lock back on any magazine, has issues where it wont fully eject the old case before it tries to feed another one, and sometimes won’t even cycle the bolt back far enough to fully extract the casing so the bolt just slams home on the already fired casing. My BCM lower came with an H buffer which I swaped with a BCM carbine buffer with the same results. I thought the problem might be the springco white action spring but does it with the factory spring too. The gas rings are in good shape passing the table test, and everything was bought new at the same time.
I have 2000 rounds down range with the first 500 rounds being PMC x-tac 62gr (hot ammo),1000 rounds of an assortment of pmc bronze, wolf, federal value pack from walmart, and federal .223 (don’t know what kind), and 500 rounds of xm193. The gun runs like a champ with 5.56 spec ammo. Zero malfunctions, robust cycling of the action, and significantly higher recoil (about 50% more based off feel). It chokes hard with all the .223 spec ammo, hard as in a malfunction every 3 to 5 rounds. All the stuff that doesn’t fire in my midlength cycles 100% in my BCM carbine gas rifle.
I understand that the midlength runs at a lower pressure than the carbine, but I need this rifle to run with 223. I know I should technically be shooting only 556 out of this gun, and there’s probably nothing wrong with my mid length since it runs great on 556, but with ammo the way it is, I have to get this running on 223.
So my main question is this: is it stupid to try and open up the gas port to allow more gas into the system so the rifle will run on 223? Im thinking of getting the gas port drilled out since 90% of my shooting will be 223 from here on out, and tuning the gun with heavier action springs and buffers when I want to shoot 556. Is this a bad idea? Also, does anyone think there’s an actual issue with my rifle? I personally think the gun is fine, it just doesn’t like 223. Unfortunately i will be shooting a lot of cheap 223 indefinitely.
Rifle set up is 16inch lightweight BFH BCM middie, BCM bcg, gunfighter ch, shaved fsb by ADCO to fit under a troy trx extreme, complete BCM lower. 2000 rounds on everything. Thanks!
There is nothing wrong with your carbine. It’s tuned to run on 5.56 spec ammo. Do not open your gas port to run 223 SAAMI spec ammo. Once you open the gas port, there’s no going back.
I am no expert on this, but you could probably tune your carbine to run on 223 SAAMI spec ammo by changing the spring rate and running a lighter buffer. It might be easiest by installing an Vltor A5 receiver extension and a lighter buffer.
With things being as crazy as they are at the moment, I would refrain from opening up the gas port because it’s difficult getting replacement barrels
Look for GAS LEAKAGE. My 14.5 middy was messing with me bad.
I found that the gas tube was too narrow where it goes into the key. Gas was leaking like a mofo. I think the tube was supposed to be .080" and mine was down to like .065. Gas was blowing out the front of the key…
I don’t have anything constructive to add, however I will say that i have a M&P15 that exhibits this exact same behavior. It runs 100% on 556, and will short stroke about 1/10 on any 223 ammo. The ejection suggests that I have plenty of gas, but I still have not been able to figure out exactly what’s going on here. I suspect that my action spring is too long or stiff (that’s what she said… yeah, ok). A lighter buffer didn’t resolve my gun’s issue. Keep us posted if you find a solution.
Check for leaks around the FSB also, and swap the BCG with your BCM carbine to make sure that’s not the cause (could be an obstructed or loose gas key).
So my main question is this: is it stupid to try and open up the gas port to allow more gas into the system so the rifle will run on 223? Im thinking of getting the gas port drilled out since 90% of my shooting will be 223 from here on out, and tuning the gun with heavier action springs and buffers when I want to shoot 556. Is this a bad idea? Also, does anyone think there’s an actual issue with my rifle? I personally think the gun is fine, it just doesn’t like 223. Unfortunately i will be shooting a lot of cheap 223 indefinitely.
Dont touch it.
I’d start with measuring the gas port size. Someone will be along soon and tell you what the spec should be at.
Again, dont touch it. I dont understand the compulsion to pull the FSB or gasblock right away to see what the gasport size is when a gun runs into issues.
OP: I have a buddy whose BCM 16mid runs ok with 223. I assume these 2000 rounds are broken down into several sessions?
When did you start running 223 through it?
Did you run 556 successfully in the same session that you had problems with 223?
Did you only start having issues with 223 after you got it back from the shop?
Out of curiosity what would be the best way to check for a gas leak? Is there another way besides tightness and specs of port and gas tube and gas key?
Was there any visual clues that it was leaking? I’m not able to take the gun apart so any disassembly will require a trip to an armorer. I do have some leakage around the gas block where the tube inserts into. I thought this was normal and would “seal” itself up after a while. My carbine gas gun looks similar.
Col croc, I started running the 223 through it after the initial 500 rounds of xtac, 1st shooting session. Second shooting session was my first class where I shot the federal and pmc bronze with embarrassing results, 350 rounds. The last 1150 rounds were spread out over 3 shooting sessions trying to diagnose the problem, swapping action springs, buffers, and BCG with a spare I have. Any time I swapped a part I ran both 223 and 556, 556 ran with every combination, 223 never ran. The upper was shipped to adco from BCM when I bought it so the fsb was shaved, and rail installed when it was brand new.
Does anyone have a pic of what a leaking gas tube looks like? Like I said above I have some leakage where the tube meets the fsb, is this normal or should there be nothing?
Well I took the rail off and took some pics of where the tube meets the fsb. There’s only buildup on the bottom half. The top looks clean, is this my problem?
What mistwolf said, mostly.
Its set up to run 5.56 pressure ammo. If you insist on running .223 and especially weak .223 like PMC then barring a definite gas leak problem, try a lighter buffer first. You can either buy one or mod the one you have by switching out the weights.
If you read my post you would of seen that I already tried a carbine buffer which is the lightest available as far as I know. I’m also not aware of a lighter action springs, only found extra power springs
True enough. And if you read my post i mentioned why it would malfunction with weak ammo. I also mentioned how to lighten the buffer. That includes how to lighten a carbine buffer. My bcm middy runs any factory ammo i have fed it including pmc and mfs steel case. It is set up as sent from the factory with the h buffer. I suspect a gas leak based on this. Your pics of the gas tube do not look exceptional to me. Mine has the same carbon deposits as yours.
Check the extractor, insert and spring on the bolt.
Is there a black o-ring?
Your BCG may be set up for a rifle if it doesn’t have the black O-ring installed, has a blue insert and a 4 coil spring instead of the black insert with 5 coil spring.
I can only speak from my sample size of one, but I have the 14.5 EAG upper and my experience was similar to yours. No issues with XM193 or the like, but Armscor or PMC bronze would short stroke - mostly just a failure to feed, but occasionally a FTE as well. After about 1,500 rounds, it now feeds anything; so perhaps there was a small break-in period to my rifle, and your’s as well. FWIW I never did switch to a carbine buffer either, I have always run it with an “H.” I know that BCM is very specific with the 14.5 middies, they do require a full power ammo.
I had an 11.5" BCM gun that had the same symptoms with .223 & 5.56. They had me ship it back to them. When I got it back it functioned
properly but no one I emailed at BCM could tell me what the problem was or what if any parts were swapped out.