That shooting and handloading sometimes!
Trial and error. At least you have eliminated the hard part, and have greatly narrowed your search.
You know. I should have just started with me
But I'm blaming Dillon
Crimp was too heavy.
I'm used to Dillon pistol dies, but Dillon does not make 327 Fed mag dies, so I had to get RCBS.
Now Dillon pistol dies start with a taper crimp and if you screw down further you are into the roll crimp. And seating and crimping are two different stages.
RCBS dies seat and crimp all in one step and I remember a lot of fiddling around setting it up. Especially because there was a metal burr on the threads and I thought I was against the case mouth when I wasn't.
I compared the 327 rounds to my 45 Colt and 38 Spcl and it did look like I had much more crimp on the 327, so before I did anything else I loaded some up with barely any crimp.
Probably still could have been tighter groups, seeing as how I was semi-resting with the lever on the steering wheel, but this is more like it.
I had only heard of over crimping affecting lead bullets, but apparently jacketed can be affected, too.
The good news is I can leave the die set up where it is and go right from the XTP's to the LWC's. The lead bullets seat a little shorter OAL, but still longer than the manual calls for and into the cannelure.
So doh (insert smacking head smiley here).
Learnt somethin' new.