08-01-2013, 04:10 PM
Keep The Change Wrote:[quote=surfcityred]Thanks so much for all of the replies to my thread. I will attempt to answer all of your questions and perhaps ask a few more.
LRRPF52: I purchased this 24" Grendel upper complete from Accuracy Systems in Colorado. You mention "lapping my bolt to the extension". How is that done? Are there any instructions or videos on line? Regarding the Grendel Reloading Handbook, I do not have one. I have been getting most of my info on line from various forum sources and powder manufacturer tables. I actually called Accuracy Systems and asked who manufactured their barrel but they refused to tell me.
QUOTE]
I would like some info on lapping bolts to the extension as well.
Lapping the bolt to the extension involves taking a sized piece of brass, cutting it in-half radially, then placing a stiff spring inside the two halves of the case.
You then remove the extractor and ejector on your bolt, place liberal amounts of lapping compound on the backs of the lugs, install the bolt with cam pin and firing pin + retainer into the carrier, assemble the BCG into the upper, close the receivers, and cycle the action by hand repeatedly until the lugs and lapping compound work into the bearing surfaces of the barrel extension teeth.
This balances out the lug contact, so that you don't have uneven stress on the critical pressured components of the system, and helps with accuracy. The technique comes from blue-printing and truing of custom-built rifle actions, and transferred over to the AR15 with competitive shooters.