Sounds to me like you're trying to shoot an incompatable bullet in your gun. I wouldn't rule out a short chamber, although I doubt thats what you'll find.I don't shoot a 444 but I do shoot a 45-70 and I'm aware of the types of problems you can have with strait wall cartriges. For example I ordered some 440 grn lbt solids from cabela's and when loaded to the crimping groove they wouldn't chamber. This is a marlin 1895 by the way,.I used my rcbs lathe type case trimmer and shortened some cases .060 " and then reduced my load slighty and they were awsome. Since you didn't say what factory load gave you the problem it's really hard to help you pinpoint the cause. as was mentioned above, too much case mouth expansion followed by a heavy crimp can also make for difficult chambering. Inspect your chamber carefully before fireing with any ammo.