BCG fubar

[Craizie]

So I went to the range to shoot my new 5.56 suppressor and sheared the gas key off the BCG after 20ish rounds. It's a 7.5" Radical arms complete upper.
Does over pressure cause this or what?

I swapped in my buddies BCG after cleaning it and lubing it and it would not cycle. It would partially pull out the spent case from the chamber and slam a new round under it side ways.

Is the upper fucked up, or what? How do I fix this and prevent it from happening again?

[svauto-erotic855]

Its sounds massively over gassed/overpowered. You need an adjustable gas block to tune it down. It also sounds like the upper was damaged in the process.

[KBScobravert]

Gas key not staked and or was loose. Now the upper is damaged. Take a look at the track in the charging handle. Look at the gas tube too. Make sure it isn't fubar also.

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[Craizie]

Gas key not staked and or was loose. Now the upper is damaged. Take a look at the track in the charging handle. Look at the gas tube too. Make sure it isn't fubar also.

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The charging handled looked fine. It had some scratches towards the front end ( gas key area ) but nothing major, just looked like the black coating was removed, no groves or anything. I probably need to take down the whole upper and inspect it, but I'll have to youtube some videos on how to do that.

[Gtracer]

The charging handled looked fine. It had some scratches towards the front end ( gas key area ) but nothing major, just looked like the black coating was removed, no groves or anything. I probably need to take down the whole upper and inspect it, but I'll have to youtube some videos on how to do that.

Remove take down pins, pull charging handle and BCG and use flashlight to inspect...cant imagine having to do much more that that considering the force that was needed to shear off the Gas Key

[Craizie]

Remove take down pins, pull charging handle and BCG and use flashlight to inspect...cant imagine having to do much more that that considering the force that was needed to shear off the Gas Key

I've done that and cleaned it up a bit, I didn't notice anything that was blatantly damaged.

[Gtracer]

I've done that and cleaned it up a bit, I didn't notice anything that was blatantly damaged.

Yeah, I am thinking that the coating on these uppers is not too thick and if the gas key sheared, the BCG damaged the upper...you would see NOTICEABLE scratch/gouge marks in the channel. If you are not seeing anything that would throw off the tolerances built into the BCG channel within the upper, then I would say that it is probably something else...though, uppers are only about $65-$80 so maybe it would not hurt to replace.


Looking over your OP, obviously the gas key must be replaced at the very least. The BCG not feeding properly has to be attributed to either added friction within the upper (damage) causing the BCG to lose velocity in the process or not enough gas getting to the key. I would suspect a leak or crack in the tube from over pressure...I would replace the gas system and the BCG at the very least since you do not see damage within the upper.

No expert and several others on here are probably more qualified than I but just looking at how the rifle operates...and process of elimination I would start there, BCG/Gas system.

[Craizie]

Yeah, I am thinking that the coating on these uppers is not too thick and if the gas key sheared, the BCG damaged the upper...you would see NOTICEABLE scratch/gouge marks in the channel. If you are not seeing anything that would throw off the tolerances built into the BCG channel within the upper, then I would say that it is probably something else...though, uppers are only about $65-$80 so maybe it would not hurt to replace.


Looking over your OP, obviously the gas key must be replaced at the very least. The BCG not feeding properly has to be attributed to either added friction within the upper (damage) causing the BCG to lose velocity in the process or not enough gas getting to the key. I would suspect a leak or crack in the tube from over pressure...I would replace the gas system and the BCG at the very least since you do not see damage within the upper.

No expert and several others on here are probably more qualified than I but just looking at how the rifle operates...and process of elimination I would start there, BCG/Gas system.

Thanks. Now I just need to figure out how to disassemble this bastard. I've built a few lowers, but never fucked with an upper.

[NoClassic]

pull the gas tube and check it for damage

[Gtracer]

Thanks. Now I just need to figure out how to disassemble this bastard. I've built a few lowers, but never fucked with an upper.

pull take down pins out until they "pop", these are the two larger pins with rounded heads located at the front of your lower (below the barrel nut) and at the rear of your lower (directly behind the safety selector).

The upper should come off of the lower without problem at this point

Once separated, turn the upper over where you can see the bottom of it, pull the charging handle out which should also pull what is left of the BCG out assuming you have not removed the BCG already. Though, I am confused because you mentioned you tried your buddies BCG and noticed the failure to feed...how did you get his BCG into the upper?

Pull the hand guard off, its either threaded or or has hex screws holding it onto the barrel nut.

Once the hand guard is off, the gas block and tube will be exposed. 2 Hex screws on the bottom of the gas block need to be loosened to slide the unit off the barrel.

The only problem you will encounter on the gas block is if the screws are staked, which they should be. A nice tight allen wrench should be able to pull the aluminum threads back in shape as you backout the screws to remove the block.

If you are using a steel block (cheapie) then you might just want to buy a new block and tube.

If you decide to keep the gas block, you will need to remove the gas tube from it using a punch to remove the roll pin.


clear as mud?

[KBScobravert]

That's the one I had that broke. It may have been my fault, but don't know. It happened after about 60 total rounds and failed on my 20th suppressed round on a 7.5 in barrel. Might have been over pressure.

That may be your problem. 7.5" with suppressor? What can is it

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[Craizie]

Aac

[KBScobravert]

Aac

Which? It is rare to find one that you can run with a barrel that short. Most want 11.5"

[Craizie]

Which? It is rare to find one that you can run with a barrel that short. Most want 11.5"

Sorry 556sd. I suppose I should have done more research on the short barrel.

[Gtracer]

Which? It is rare to find one that you can run with a barrel that short. Most want 11.5"

yikes....I hope my 10.5" 300BLK doesn't have this problem once my SBR stamp comes in