Fte, ftf bca 20" grendel.

[LR1955]

BJ:

After all those checks, next I would look at the buffer and buffer spring assy.

If I had a problem with an AR that I couldn't fix, I would get it to Montana or LRRP52.

LR-55

[LRRPF52]

So I got home and checked it all out. Everything looks good to me. The only thing I did was drill the gas port to 3/32. It was only a tiny bit smaller maybe a couple thousand. There was an insane amount of carbon for very little shots taken i only shot wolf and hornady black. Weird. Any other ideas?

Where are you seeing the excess carbon?

If the carbon is leaking around the gas block, you can see it around the journal from the port. Most after-market gas blocks are made for ease of installation by people at home so they can get them on, whereas factories that install gas blocks with a correct seal use jigs that require significant mechanical advantage to press-fit the block into place.

The TDP calls for a very tight, sealed-gas fit of the FSB to the journal and correct port alignment.

The next place for gas to leak is the gas tube/gas block interface. Again, DIY set-ups are meant to slip-fit, real ones are press-fit/interference fit/tight.

Next place for gas to leak is the gas tube flange-to-carrier key fit. More common on RLGS high-volume guns, easy fix with a tube replacement and correct alignment job (hard to do well sometimes).

Next place for gas leak is the carrier key-to-carrier fit. Colt has been using a form-a-seal aviation-grade sealant compound which is basically a temp-rated Loc-tite, along with higher torque spec for CLGS on M4, whereas RLGS 5.56 doesn’t need as much torque. US Grade 8 fasteners with temp-tolerant sealant on them as well.

Next place for gas leakage is the fit of the bolt tail inside the final aperture for it in the bolt wall between the expansion chamber and firing pin stop area.




An inefficient gas containment carrier/bolt interface will allow carbon to spill out into the FCG area in your lower, which is why I asked where the carbon was.

These and about 150 other reasons are why I’m a strong proponent of prejudicial parts sourcing and installation into a build.

I simply don’t trust anyone to build a part right, so I have to look at them all before I let them into a gun.

I normally don’t even pipe-in on a BCA thread because they should be paying us a Customer Service fee to help people with all their parts, but this might be as simple as a gas block issue.

No pics so it’s hard to see what’s going on.