First off, let me start by saying I have read through a whole bunch of 9mm leading threads and I've checked a few things first to try to solve this on my own.
Some stats:
I'm shooting a CZ SP01 that has been throated by DougGuy
Barrel slugged at .3555 and I'm shooting cast that has been sized to .358
I'm using Hi-Tek coating. This is the second batch I've done with this and the first batch gave me no issues. This batch also passed the wipe and smash test, so as far as I can tell, the coating was properly applied.
I pulled loaded rounds and the boolits all still measure at .358, so they are not being swaged down by the case or crimp (using Lee taper crimp die)
Alloy is COWW, and I think is around bhn 13 or 14
Using VV N320 powder and the load is right in the middle of the scale, so not too hot, not too light. Same load I've used for commercially cast lead and also had no issues in the past.
This is what the barrel looks like after about 20 rounds. I ran a wet patch followed by a dry patch through it just to make sure there was no carbon fouling to muddy the results. Also I now know how hard it is to get a decent picture down a barrel using a cell phone