Monty,
Rim thickness or even diameter can be a problem- it wasn't with my cousin's 380, but was with my 310 cadet and various 8.15x46Rs.The "school solution" is to thin it from the front, like your buddy said or with a lathe.First, you can find out how much has to be removed by inserting the cartridge backwards into the rim recess,the amount the rim stands"proud" is the amount that needs to be removed. If it will not go in at all,the rim diameter needs to be reduced.If it goes in and is flush, you need to put a radius on the front side of the rim, similar to the one on the back.All or any combination of these conditions can exist.Once you id the problem, the next consideration is to determine how to correct it. If you use a drill press(or a lathe for that matter), it will be difficult to get to the front of the rim with a file and still be able to "chuck" the case on a solid area, to avoid crushing the case.This can be avoided by inserting a bullet diameter rod( or even a jacketed bullet)into the case and chuck the case, backed up by the rod.I found out, with the 310,that rim could be thinned from the rear, and the primer pocket deepened with a Lyman primer pocket uniformer and still have enough "meat" to hold the pressures.In this case only .005" was removed ( as a side benifit, the 32-20 headstamp was removed at the same time). If you try this,section a case that will chamber, to verify it isn't too thin).I hope this helps,all this is what makes this game fun.
Mike
