This was posted elsewhere as well, regarding this older thread which is archived so could not post in it....

https://www.ar15.com/forums/Armory/CMMG-RDB-9mm-Chipped-Bolt-Lug/48-511703/

Hoping maybe there'd be some direct feedback from CMMG.


I have only about 2200 rounds through mine and I've got chips on three bolt lugs.  Been having a lot of FTE and hangups with an 8" barrel, but none on a 16" barrel.  Have replaced the extractor and ejector springs several times and again, with 16" barrel it holds up fine, but with the 8" barrel once it starts to get hangups can't shoot more than 1-2 rounds before another.







It's clearly not wear or smoothing over, but chipped/broken edges that have a ragged and sharp feel.  Hoping it hasn't gouged the lugs on the barrel extension.  Would like to hear from those in the older thread as to how they dealt with.  I have a 'repair kit' that has an extra bolt, but I's also like to know if CMMG can replace this damaged one.

Update: went to the range with just the 8" upper with new replacement bolt.

Ran like a top, 200 rounds and change, not a single hang-up or issue, bolt locked open.  115-gr factory Blazer Brass, and 147-gr subsonic through an Omega 9K suppressor.  H1 buffer.  Fast strings of doubles and triples, even some tac reloads which would be the death knell before.  Ejection was a consistent and healthy 4:00-4:30.

So it would seem (again only 200-250 rds) that the chipped bolt lugs were the issue (again only with the shorter 8" upper but not the long 16"?), but I can't help but wonder if like before it's fine n the beginning but will soon just all go to hell.  I'm still pretty confident in my longer upper getting through a match as it has each time, but the shorter one for 'fun' matches and maybe even some home defense with suppressor...still wary.  Can only tell if it's really fixed if it holds together up to 1000 rounds or so.  Last round count where it went bad after refreshing the extractor and ejector springs was only around 450.

Will see if CMMG will still offer some sort of replacement for the damaged bolt.

At least from the looks of out (again only first 200+ rounds), the lugs/edges seems to be fine but you can see wear the brunt of the contact wear is.  Except the second and third lug after the extractor seem to have their leading edges at an angle compared to the rest.  Don't know if that's from initial wear or by design.

Good news!

CMMG got back to me and will be sending me another bolt, so at least I'll have an extra backup.  Much appreciated to them for responding.