ive got 4 kinds of 45-70 brass. remington nickle plated, remington brass, hornady brass, and winchester brass. all are cut the same length and have the same wall thicknesses. i load all of them exactly the same but i do segragate them by brand. i decap them, prime them, run them through my lyman m die. then i charge, place a wad if im using one, and then seat the bullet over my black powder. when i load the winchester brass it either crushes it or the bullets pull out and stick in my die. it only does it with the winchester brass. i can load a remington fine, then load a winchester which crumples, then i load a hornady or remington and theyre fine. i then have to put about 15 grains of varget in the case and pack it with oatmeal and fireform it again. ive tried annealing them but it didnt seem to help. should i assume i got bad brass and get some new stuff? should i write winchester a slightly nasty email.

i had similar problems with 45/70 WW brass (case mouth crumpling). i have Remington, Federal and WW brass. i beleive ww is the thinnest, i know it is the lightest and most case capacity. Be sure you are starting the bullets straight into the case and not catching a grease groove on the way in. I found the federal cases cut the bullet, but the ww crumpled. i'm very careful now seating bullets straight.

Are you treating this as a straight walled case and flairing/belling the case mouth?

The 45-70 has to be loaded like a targe pistol round. The case mouths must be belled and preferably with something like the Lyman m die with 2 steps to get about .050 of the bullet base below the case mouth by hand.
If you use a second rate seater with appor nose punch with one of the short 300 grain bullets you may still have a problem.
Take case to start the bullet into the case straight wioh your fingers before seating.

craveman85: before you go Postal on the village idiots at WW, try running the cases farther into your M die. As SR4759 says try 0.050" and if that dosen't work go to 0.1" and try. Your seater should iron out any belling on the case. Look at it this way, you are loading a big long 45 Colt that uses .458" bullets.