I'm back with the same problem on different rifle and different can.
Rifle: Savage 22-250.
Load: 73 ELDM with Superformance.
Can: Dakota Silencer Varminter 3.0 223 cal.
Interestingly, out of my 3 cans, it only occurs with 1, and only occurs if I let the rifle / can cool for a few minutes between groups. Compare the "V3 Cold" groups with the others. Same rifle, same load, same range session.
The "V3 Hot" group was shot with the same can, right after the upper left "V3 Cold" group with no cooling time. While not the greatest group, it clearly does not have the 1st round flier problem.
I have demonstrated this behavior more than once with the same rifle and load. Here's another target from an earlier range trip:
I've seen a few other threads like this, but no one seems to have any good theories for why it happens. Considering changing the can fixes the problem, we can be certain that is a factor. However, before we blame the can exclusively, I'll mention that I have been using this same can on a 223 AR15 for years, and have never seen this happen there.
My next test will be to change the load to see if a different powder and bullet makes a difference. I'm going to work up the 53 v-max with H4895.