10-10-2019, 02:54 AM
lazyengineer Wrote:That wasn't really my experience as being a need. With the PSA upper at least, it came from the factory quite square.
As to lapping being "easy", it's doable to an enthusiast who has all the right tools and gumption. I don't consider it a reasonable expectation for this to be a normal part of ownership for everyone to do. And that's one of the challenges of Grendel; it's pushing some engineering boundaries for the purpose of delivering impressive performance. But no other round has people encouraging lapping over fear of breaking bolts if you don't.
LRRPF52 Wrote:The first uppers I heard about out-of-square uppers breaking bolts were 5.56 and 7.62x39.
The principles are the same regardless of caliber/chambering, so I wouldn't call it cartridge-specific condition at all.
I hadn't heard of a connection between bolts breaking and the upper not being square on other calibers, just here on the 6.5 Grendel site. I think that has more to do with the case rim size, since there's less meat on the bolt lugs than on 5.56. That's not to say it doesn't happen on other calibers, I just think it applies more to cases with a larger diameter rim like the Grendel.
Even with other calibers I have heard positive things about lapping the upper before assembly. Mostly it was for accuracy. I didn't get around to buying the tool 'til I built my Grendel, but I plan on lapping my uppers on all my future builds now that I have the tool. I will probably tear down some of the old builds as well, starting with the least accurate, but it is not a high priority. I'm curious to see what difference it makes on them.
Thanks for posting your experience with it.