
Originally Posted by
LRRPF52
When I build up a carrier and key, I like to start with a stripped BCM carrier. Used to be able to get them that way. Whoever they had as a supplier at one time had a really nice, smooth grey surface.
Anyway, the carrier key is supposed to be made of a softer steel, but still has chrome lining in the bore where it telescopes over the gas tube. For a long time, many low rate companies sourced keys that were harder steel, without chrome lining.
I modified my Brownell's staking tool so that the screw heads are rounded and not sharp points, to provide a better stake with less galling of the carrier key body.
I strip the carrier and key of grease with a good cleaning, then acetone bathe them so they're bone dry. I like to rough texture the surfaces that will be joined so they take a sealant better, and I have used Red LT #271, but would also consider Rocksett as well. US made grade 8 fasteners, also degreased and acetone bathed with Red LT 271 and a torque driver finish the assembly. I usually test fit before using sealant to make sure the key is aligned with the gas tube aperture in the face of the upper.
Once they are together, I use the staking tool to put the stakes in, and will re-phosphate the impinged areas. I know the TM doesn't call for sealant, but I prefer it.
I also recommend against staking the key with impact. The tools like the MOACKS and the Brownell's use compression, which isn't going to knock the seal loose. The TM also has an interesting treatment for deformities on the carrier key mouth. There's a tool for re-forming that, using impact with a small brass hammer.
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