Glad it worked out for you. Case bulging can be caused by a number of reasons. A lot of them have been stated here.
As stated before, the 45-70 case should not have to be full length sized. If you do full length size it, you can get springback that causes the "coke bottle effect". The sides of your case look like this: ) ( This is a little exagerated of course, but it is really noticable when using carbide dies on long straight wall cases like 357 max and 445. Only size enough of the case to hold your bullet. No more. If you get a bulge at the base of the bullet, you are getting into this narrowing area of your brass.
Are you belling your brass before seating your bullet. Cast bullets, even if gas checked, should be inserted into a belled case mouth. This not only helps keep the bullet straighter when seating, it removes some of the initial stress in getting the bullet started into the sized case.
What does the seating stem in your seating die look like? Are you using a round nose seat with a round nose bullet and a flat nose seat with a flat nose bullet? A sure way to leave a bulge in your case by using the wrong seating stem and starting the bullet crooked. If you don't have a seating stem that matches your bullet exact, a little JB Weld and release compound can be used to form a tip on your seating stem that matches your bullet. Put a little vaseline, pam spray, or similar release agent inside your die. Screw the seating stem down as far as you can while still allowing you to put the bullet up into the die. Put in a ball of JB Weld and push the bullet covered with release agent up into the die to form the die punch. Allow it to set for a couple of minutes and pull the bullet out. If you don't use release agent on the die, you will have JB Weld stuck to the sides of your die walls. If done properly on a straight wall case die, the punch will last for years and will not harm your die at all.
When it comes to crimping, there are several things that can cause bulging cases. Die set to deep and trying to "over crimp" the brass can cause bulges at the base of the brass near the case head. Seating stem set too far down in some dies can allow the bullet to start crooked. Over crimping into a cannelure can cause the base of the brass to bulge. Crimping in the wrong location on a cast bullet can cause the case to bulge.
I seat my bullets so the cannelure or crimp groove of the bullet is seated into the case mouth. You want the mouth of the case even with the edge of the cannelure or groove that is closest to the bullet point. As you crimp the brass, it is going in and actually compressing down a little. Having the cannelure and groove down into the case mouth allows your brass to radius without much force and the outside edge of brass case mouth actually ends up about middle of the groove or cannelure.
Are you seating the bullet and crimping at the same time? Thats like trying to close your garage door at the same time you are driving the car into the garage. Might work some of the time but eventually the door is going to hit the car.
Seat the bullets with cannelure or crimp groove even with case mouth as mentioned above. After all the bullets are seated, you can readjust your die. Turn the seating stem all the way up and start turning your crimp die into the press with the ram in the up position. Screw in the die until you feel the die make contact with your brass. Raise the press arm and turn your die an additional 1/16th of a turn. Try to crimp. You can feel it if it crimps. You want the press ram to cam over on your crimp. If you keep adjusting in 1/16 turn increments, you can see the crimp start to develop and can feel it. When the case mouth is directed toward the bullet, you are done. You don't have to cram the brass into the bullet to have a good crimp. A nice and even roll into the groove is all you need to raise pressures or hold the bullet. If you were to tap the bullet like you are tapping it into the case, the top ring of the crimp groove or cannelure should come up against your brass. This is just a knife edge and that is all it take as long as you are symmetrical all the way around the case.
Like I said before, I am glad the folks who responded before me helped you out. This is a good topic and I just wanted to add another 2 cents that may help someone else someday.
Steve
