Shortest 300 blk barrel

[dellet]

What is the load?

I would try slugging the barrel. Or if you have a good way of catching a bullet, shoot it without anything on the muzzle so you know nothing is happening there.

If you mark the bullet and index it, I would expect there to be a mark on the bullet where it passes the port or other rough spot in the barrel if there is one tearing the bullet. If you set the index mark around 11 before pushing the bullet through the mark will be real close to 12 when it passes the port.

[gemihur]

The 300BLK was designed for a 9" Bbl with a 7" can.
This according to AAC. Who borrowed it's design from J. D. Jones's 300 Whisper
The 30/221 had been used for sometime.
I prefer the 30 Raptor by Reeder (shown here next to the 300BLK)