Never had any issues with that magazine and factory ammo?
Maybe it is not the magazine.
I have seen very hot loads override the base of the round, but dig in around the center of the cartridge. About half of the cartridge gets pushed out of the magazine but since the bolt is halfway up the thing, you get a jam.
Someone with experience with BL-C would have to chime in and say if your load is hot. I don't shoot 55's or BL-C.
If I'm not shooting, I'm reloading.