Not enough velocity to stabilize that heavy bullet. Combined with the short barrels = key holes

Is there a reason to use those heavy bullets?? I have wonderful performance with 150 grain bullets.
Most people loading the 220 bullets are striving for shooting them through a suppressor, and staying SUBsonic. You didn't mention that in the post.

So, unless that's your goal, go lighter on the bullets, and you'll have much better success.

BTW, I ONLY EVER use Lil Gun powder for my 300 Blackout loads. It's got a perfect burn rate for the chambering.

And, properly neck sized (Full length sizing only!), there will be enough friction between the necks and the bullets to hold onto the bullets while the powder all burns inside the case , before the bullet leaves the case mouth. So, no need to ever crimp (unless you are seating cast lead bullets, after "M Die/Lyman" expanding the necks.) Otherwise, no crimps, and you will get better consistancy of the velocities.