I bought one of the BCM low pro gas blocks and installed it, all went pretty well with one small issue. So I sent an email to bcm but didnt really get much of an answer so im hoping someone here might be able to help.
Email i sent to BCM:
How tight should the gas block fit on the barrel before set screws are tightened? I installed mine, its not lose enough to rattle, but it is easily rotated with almost no resistance before tightening the set screws. This is on a standard M4 style BCM upper, government profile barrel, carbine gas system. I test fired the rifle and got a couple failures to feed through one mag so i am trying to figure out what could cause that. It ran flawless before. Thanks.
Im 99% sure it is aligned properly so im not sure what else it could be, i figured i would be saving myself some trouble buying a BCM gas block for my barrel but apparently something isnt quite right.
like i said, im 99% sure ive got it lined up, and the hole of the port in the block seems to allow a small level of inaccuracy even if i was off slightly. And like i said it was about 30 rounds, its all the time i had earlier, and there was probably 3 times where it didnt pick up a round and went click and failed to feed maybe twice.
Oh wow, I didnt even know they had gasblocks until this thread came up.
How tight should the gas block fit on the barrel before set screws are tightened? I installed mine, its not lose enough to rattle, but it is easily rotated with almost no resistance before tightening the set screws.
Your situation appears to be normal in that it is supposed to fit that way prior to tightening… Any chance you didnt tighten it enough that it shifted when you fired it? Is it still on tight now that you’ve fired it?
Also, just curious, where did your rear set screw mount in relation to the rear FSB pin channel on the barrel?
Seemed to be tight after firing and i got the set screws as tight as i could with out stripping the heads. The front set screw is set into a dimple in the barrel as per BCMs instruction, so i dont think it moved when firing, and the rear screw just avoids the channel for the FSB.
There’s adimple up front or are you referring to the front fsb pin’s channel? Sorry for the questions but it’s hard to tell without personally handling your weapon or seeing pics atleast. I ask because stripped bcm barrels have a dimple for the rear set screw and that’s probably what the instructions are referring to. Without seeing your barrel, i cant tellif it has that same dimple or not. My guess is it doesnt since you bought it as an assembly with the FSB. In anycase, if you have it on the front channel, it may be too far forward partially covering gasport, hence, your issues
You need to ensure that the gas block is sitting just in front of the groove around the barrel for the handguard cap.
Put red Loc-tite on the screws and then set them in place. The screw should sit right down in the dimpled hole.
Make sure that the carrier key mates up to the gas tube properly. I would also check the inside if the key with a small zip tie or wire to ensure that there is no obstruction.
Did you remove the FSB and then install the low pro yourself?
If all else fails contact BCM as per the site rules.
The gas block seems to line up when against the groove. Here it is all the way back rotated 180 degrees to the set screw hole that lines up with the port in the top of the gas block.
Something else i noticed when taking it apart, there is alot of crud on the bottom of the gas tube, i never paid attention to notice if it was there when i took the old one off so i dont know if it is significant.
I am no expert so by all means correct me on anything i may have done wrong.
You need to ensure that the gas block is sitting just in front of the groove around the barrel for the handguard cap.
Put red Loc-tite on the screws and then set them in place. The screw should sit right down in the dimpled hole.
Make sure that the carrier key mates up to the gas tube properly. I would also check the inside if the key with a small zip tie or wire to ensure that there is no obstruction.
Did you remove the FSB and then install the low pro yourself?
If all else fails contact BCM as per the site rules.
see pic
i dont want to loc tite until it is running right because who knows how many times i will be taking this thing apart.
seems to be mating up properly, and i put a zip tie through the gas key, no obstruction.
yes i removed and installed myself.
i emailed BCM, what i got back was: "Single dimple for the first set screw. They are degreased , set in dimple, and high temp loc-tite.
Take about 20 min with MAP gas to remove. Very secure. This is how we install them here. We do recommend a military trained armorer install this for proper fit and function. "
Thanks alot for the help though, any possible ideas help me out.
I don’t quite understand. The BCM barrel should be dimpled for at least one of the set screws on the BCM gas block so alignment side-to-side and front-to-back shouldn’t be an issue. You should be able to just slide it on, line up the dimple with the set screw, RockSett the set screws and tighten them down. I’ve used low-pro gas blocks on three different BCM barrels and it wasn’t any more complicated than that. I have, however, always elected to send the assembly off to get the gas block pinned, unwilling to rely just on the set screws.
If you’re using Loc Tite brand, be aware that barrel temps under the front sight can reach temps that exceed the capability of even High Temp Loc Tite (266) at some rates of fire and it can definitely loosen. RockSett will hold up to 2000 degrees F, would likely be a better choice in a high temperature application.
im going to give it a try again the next time i can get out to the range, if the problem persists i guess ill get into contact with bcm again.
I don’t quite understand. The BCM barrel should be dimpled for at least one of the set screws on the BCM gas block so alignment side-to-side and front-to-back shouldn’t be an issue. You should be able to just slide it on, line up the dimple with the set screw, RockSett the set screws and tighten them down. I’ve used low-pro gas blocks on three different BCM barrels and it wasn’t any more complicated than that. I have, however, always elected to send the assembly off to get the gas block pinned, unwilling to rely just on the set screws.
there were no dimples when i took the old front sight/gas block off, just the holes for the old pins, i made a light dimple for the front hole which seems to work, no evidence of movement as far as i can tell, and i cant move it with my hands even when applying a good amount of force.
I said that before I realized that you removed the FSB and put a block on. I would put the FSB back on and then cut and grind it like a low pro block which I have done numerous times now.
I wanted to do it in i way i thought would be better, instead of dremeling a FSB, i would buy a nice one from BCM and do it the “right” way. But apparently something isnt working out. Im not an expert or anything (obviously ) but as far as i can tell i didnt make any major errors installing so im not sure whats going on.
I would put the FSB back on and then cut and grind it like a low pro block which I have done numerous times now.
I may end up having to do that, im going to give it another try next time i can get to the range (.223 and 5.56). If it doesnt work out ill see what BCM has to say and if it comes to it i may end up breaking out the dremel. Thanks for the help.
Seems to be whats going on, i only had time to shoot maybe 30 or 40 rounds so i cant say its for sure whats going on but that seems to be the problem. It locked back on the last round. Im honestly not sure what buffer is in it, it was assembled by a friend, but it worked fine before for 2000+ rounds on the old gas block. Gas key is secure and staked, it doesnt look like anything is blocking anything.
Buffers are identified by the markings or lack thereof on the buffer face. Plain is the standard carbine followed by H, H2, H3. Each weighs a different amount.
