After 123 rounds???!!!

[Nukes]

Was the receiver face squared? If the bolt isn't in correct alignment with the barrel, I believe some bolt lugs can be stressed more than others, as they are all not sharing the load equally.

I did not specifically ask that, but I assumed (yes, I know) that was done. Seekins receiver set and Krieger barrel built by Mark Gordon at SAC, that didn't seem like a question I needed to ask, but I will ask him tomorrow.

IIRC, didn't you send the entire upper to LBC, Nukes? I thought they'd given it a clean bill of health...

If you have any left, I'd change nothing but the bolt. Shoot the same ammo. Lord help ya, if you break the Hard Use bolt, though.

Only the bolt is LBC so I did not send the upper to them. I sent the rifle back to Mark only after the second LBC bolt failed.

Also, were your listed max loads determined by you (starting low then working up, looking for pressure signs, using a chronograph, etc), or simply referenced from a manual?

28.5gr of 8208 under a 123gr bullet is often exceeding max in my experience with numerous barrels. Using 8208, I usually stay below 28.0gr.

For this rifle I started 10% below the published MAX and used 0.1 grain steps up to MAX and not beyond. Obviously the lighter charges showed cute little primer dimples and the near MAX loads showed a real primer impression, but no cratering, piercing, or even wide flat primers. Reviewing our chrono data showed no worrisome plateau for the reloads and all of the 8208XBR loads (whether 123 Scenars, AMAX, or SMK) were 100-150 fps below the AA factory 123 gn Scenars.

...Its been a while since we had a batch of broken bolts, and it would be interesting to know if both were from the same batch, which might indicate a heat treat issue.

The replacement bolt packaging for the LBC bolt is with the rifle at SAC, but I do not recall seeing a lot# listed on the packaging or invoice.

That sucks, my take home from this is to skip the Wolf ammo. If it is the metallurgy of the bolts nothing will help that except a correctly made bolt. It is good that you have spares. That was another take home lesson for me from this site. ...

Before this happened I ordered another hard use bolt :-) Some of our long range matches have had shorter range (400-600yd) run-and-gun stages. Because the Wolf shoots about 1.5 moa (double the AA factory ammo) and the brass is lousy, I figured I'd shoot the Wolf and let the brass lay. Yeah, I know—I actually decided to shoot less accurate ammo for a match. Even though I am in the bottom tier of our group's precision tactical shooters (and there are also 5 nationally ranked people who are in our matches), I had perhaps unjustified confidence in overcoming the Wolf ammo :-)

Well, since I have 3 AA bolts available, I might try the Wolf ammo paired to an AA bolt.

I don't think this is accurate.

Not long ago there was a thread here where a guy was having similar problems with an LBC bolt. I want to say he tried 2 more with the same sheered lug results. I believe he recently posted that he got an AA hard use bolt and the weapon is operating fine suppressed.

It was hypothesized in that thread that LBC was using 8620 for their bolts. I suspect that's what happened here.

Given the quality of the parts and Mark's excellent reputation (and the sister rifle he built in 5.56 NATO runs like a sewing machine and shoots ragged 100 yd holes with Lapua factory 69 grain Scenars), I am inclined to suspect the LBC metallurgy (and the known weakness of the Grendel bolt design).

That said, I will ask Mark about receiver squaring and the barrel extension.