Monster Bolt headspace issues

[Jeepster18_88]

I finally got around to building a few Grendels that I had bought parts for a few years ago. I had gotten some Satern Liberty barrels and I know that they don’t have a big fan base here but I couldn’t pass them up. I have been getting good accuracy but every once in a while the first one wouldn’t fully close the bolt. I started reloading for the Grendel and my reloads would do it more often even though I was seating the bullet even deeper than the factory load. I measured the lands and I was way way off of them.

I tried the second upper and it wasn’t closing on probably half the rounds. I would have to use a cleaning rod and beat the round out while trying to open the bolt. By the time it broke loose, the bullet was crammed deeply into the case. I finally realized that it was the headspace itself that was off. It appears that the brass itself is getting stuck at the shoulder/neck area.

I tried a bolt from Grendel Hunter and it functions perfectly 100% of the time. I don’t have headspace gauges but I tried the Monster bolts in all my other Grendels and the others won’t close at all on factory ammo. I understand the concept of tolerance stacking but 6 different barrels and not one of them will reliably close the bolt on factory ammo certainly sounds like it’s out of spec bolts. They all work fine with any combination of the other bolts I have. I know that these have a good reputation here which is why I bought them in the first place. I’m not really sure what to do with them since they won’t work in any of the barrels. I emailed them over at SixFiveArms and hopefully they can help.

[Old Bob]

Measure the depth of the bolt faces on your Monster bolts. They should be .135". If they're .125", that's the depth for 7.62X39 bolts.

[VASCAR2]

The spec for 6.5 Grendel bolt is .136 bolt face depth with a tolerance up to .002”.

I suggest you compare the bolt from the Grendel hunter to the Monster bolts. Measure the bolt face depth, length/width of the lugs and the bolt overall length. I have several Monster bolts where I have compared all their dimensions and they all are vey close.

Honestly with the track record of short chambers on Satern/Liberty barrels I wouldn’t be surprised to find more variations in the Satern/Liberty barrels than the Monster bolts. There was a group buy of Satern Liberty barrels where the chambers were out of spec. Instead of owning up to the PTG reamers not being SAAMI spec S/L went on to bash the 6.5 Grendel design then offered the Grendel II chamber. This debacle hasn’t helped S/L reputation on this forum.

I have two Friends who bought Satern/Liberty barrels sold as Brownell’s house brand. Both have short chambers and are over gassed. One barrel would not cycle factory ammo and destroyed a bolt in short order because it was so over gassed. Using hand loads with an adjustable gas block permitted this barrel to function. The barrel was accurate so the owner decided to keep it.

If I were in your situation I’d measure the seating depth of various bullets in each barrel and record where the bullet is into the lands. I have two Faxon Group buy barrels, a 16” & 18”. Using the same bullet in a Hornady COAL comparator tool the same bullets are within .003” on average. So close it is hard to get exact measurements with the tool.

I think if you take careful measurements you should be able to get an idea of the issue. I’d compare the seating depth of bullets in your Grendel hunter barrel to your other barrels.

[Jeepster18_88]

Thanks for the help. It turns out that the extractor had an O-ring that wasn’t needed. Somehow it would bind the case into the chamber so tight that it had to be beaten out. I don’t even understand how it’s possible but I measured everything on the bolt and it was in spec. It was only hanging up intermittently on the Satern Liberty barrels but it was failing to fully close the bolt 100% of the time on my BA and other barrels. I had already measured to the lands and knew that I was nowhere near contacting.