Mike,
There was some flap about this time last year on another shooting forum concerning magazine detonation in the Marlin .45-70's. Seems that some hot loaded +P type factory ammo had been involved in a magazine detonation in one of these rifles.
To tell you not to worry about a magazine detonation perhaps would be irresponsible, but the only way that you could possibly get a primer to be detonated is if the edge of the bullet nose, at an angle was centered on the primer of the cartridge ahead of it. This IS possible in the Marlin .45-70's as well as the .450 Marlin, in that the magazine tube has a "fish-belly" in it directly ahead of the loading port, which allows the cartridge being loaded through the port to "bend-the-corner" into the magazine tube. It is in this "fish-belly" that the cartridge is not aligned totally straight in the magazine tebe and the condition described above might occur.
The obvious sure, cure for this condition is to make sure that you have a flat frontal surface on your bullet that is considerably larger than the primer diameter.
Perhaps this isn't the concrete answer you were seeking, but it's the most responsible I can offer at this time!
God Bless,
Marshall
