08-12-2012, 09:36 PM
The bullet weights don't really matter as much as the bearing surfaces and velocities you intend to push them. I think 1/8.5 seems like a good compromise, but Bill A. found that 1/9 worked better for some reason after a lot of testing with the Grendel/AR15.
The traditional school of thought is that longer bearing surface pills need a faster twist, which makes sense. My buddy who has a 22" CZ527 Grendel is getting 2650-2700fps with 139gr Scenars on top of N140, so you will be looking at muzzle velocities that are no longer limited by the 50k psi AR15 bolt.
This means a lot of the longer and heavier pills can be pushed at faster speeds, but I think the 129gr SST run at 2600fps would be an awesome cartridge for this. So would the 125gr Nosler Partition, or any of the 140gr hunting pills.
Another awesome bullet I wouldn't rule out would be the 156gr Norma Oryx, which is devastating in penetration and expansion, even from lower velocities. I saw what it can do this past winter on an unbelievably large rabbit, and it left a 4" exit on him out of a 6.5 Swede going pretty slow.
I would consider going with a 20" pipe, but it won't make a huge difference in mv. Looking forward to seeing how your build turns out.
The traditional school of thought is that longer bearing surface pills need a faster twist, which makes sense. My buddy who has a 22" CZ527 Grendel is getting 2650-2700fps with 139gr Scenars on top of N140, so you will be looking at muzzle velocities that are no longer limited by the 50k psi AR15 bolt.
This means a lot of the longer and heavier pills can be pushed at faster speeds, but I think the 129gr SST run at 2600fps would be an awesome cartridge for this. So would the 125gr Nosler Partition, or any of the 140gr hunting pills.
Another awesome bullet I wouldn't rule out would be the 156gr Norma Oryx, which is devastating in penetration and expansion, even from lower velocities. I saw what it can do this past winter on an unbelievably large rabbit, and it left a 4" exit on him out of a 6.5 Swede going pretty slow.
I would consider going with a 20" pipe, but it won't make a huge difference in mv. Looking forward to seeing how your build turns out.