Sorry if I missed this, but what powder and charge weight, and your OAL?
Brass is different lengths and headstamps. Berry’s 180gr plated bulletsSeat/crimp works ok for bullets with cannelure or crimping grove as they are more forgiving but if your brass isn't exactly the same length and it starts crimping too soon you get bulges around the neck.
Different headtstamps. Just happened to get this 10mm during the current shortage. Can’t find brass so it’s all from mixed bag ammo.Is your brass all one headstamp? Is it possible some of your brass is bulged and it has only been by chance that you've loaded bulged cases with powder?
If a dedicated crimp die is on the table, I really like the Redding crimp dies. Seating and crimping in one step is not unreasonable to do, but it is easy to have something go wrong. I do this regularly with revolver load and cast bullets that have a large crimp groove.
Also, take the dummy cartridge that wont chamber and coat it with ink from a sharpie marker. Drop it back into the chamber and try to rotate it. This will reveal the contact areas.
I’ve tried with 2 different minimum loads- AA#9 and Power Pistol. It’s my understanding you can get overpressure going less than that. Reading around other forums on this die set that a taper crimp can be done with this die set but really finicky, hence why they came out with the newer set that is named taper crimp. Why they made a die set for a semi autos cartridge without making it taper crimp blows my mind.@Bluedsteel45 If I understand correctly the only difference between the rounds that plunk and the rounds that don't is powder? Try a little less powder maybe. I agree with seating and crimping in separate operations, and I second using Lee FCD, but that doesn't sound like your problem (Yet). For sure 10mm needs taper crimp.
I’ve tried power pistol and AA#9 in brand new cans. I’ve been getting consistent throws.Something up with that powder charge. Could be too much of a low density powder mistaken for another powder/charge weight. Hairy things can happen when a pistol goes boom.
What I suspect is happening is your scraping off bullet/plating as your seating and crimping creating a small ring of material that builds up in the die. This affects the quality of the finished product from bulged brass to excessive crimps to OAL variations. I've seen it before and it's a common frustration for new reloaders.Brass is different lengths and headstamps. Berry’s 180gr plated bullets
Different headtstamps. Just happened to get this 10mm during the current shortage. Can’t find brass so it’s all from mixed bag ammo.