Are you sure you have the gas set correctly if using an adjustable gas block. All the PSA 6.5 Grendel uppers appear to ship with an adjustable gas block. The Millennium Monster Logo bolts normally are held to close tolerances. I have three Monster bolts and they are all very close in my measurements. The only issue with a Millennium bolt can be the extractor corners might be a little sharp or pointed which can leave fang marks on the case rim. Not a real problem and quickly alleviated with a file or sand paper.
You might have gotten into a bad batch of PSA 6.5 Grendel bolts.
You could have a tight chamber and the bullets are into the lands causing the bolt lock up problem. Id color the nose of the ammo with a felt marker to see if the bullets are getting stuck in the lands. Id also remove the BCG and drop cartridges into the barrel. Raise the muzzle the cartridge should fall out under gravity. If you have to use a cleaning rod to push out the cartridge (factory ammo) you might have an out of spec chamber.
Remember when reloading a 6.5 Grendel you have to bump the case shoulder back approximately .003 when resizing otherwise youll have chambering issues.
You might have gotten into a bad batch of PSA 6.5 Grendel bolts.
You could have a tight chamber and the bullets are into the lands causing the bolt lock up problem. Id color the nose of the ammo with a felt marker to see if the bullets are getting stuck in the lands. Id also remove the BCG and drop cartridges into the barrel. Raise the muzzle the cartridge should fall out under gravity. If you have to use a cleaning rod to push out the cartridge (factory ammo) you might have an out of spec chamber.
Remember when reloading a 6.5 Grendel you have to bump the case shoulder back approximately .003 when resizing otherwise youll have chambering issues.