I had read a while back that light charges of pistol powder, similar to what we were using, had problems like secondary explosions . Apparently if the rifle wasn’t kept muzzle up the powder in the case would no longer lay on top of the primer, and when fired would cause serious trouble. I can’t remember where this information came from as I said it was quite a while ago. . That’s why we went with the floral foam to keep the powder on the primer.
Very true, and in the old guns it is a very large issue. In the modern lever guns or #1's, really strong guns, not so much of an issue. But yes over on the black smokey forums real light charges of pistol powder are generally frowned upon. That said a great many people do it, and will go to their grave defending it.
I look at it this way, If I can afford a x.x grains of Trail Boss (very popular) and I can't afford 42 grains of N135 (Nice low pressure load, sub teens with a 405 bullet, but don't ever use loads some idiot on the internet posts up) Then I need to find a new hobby.
Now during the height of the shortages when large rifle primers are as hard to find as hens teeth I did go off into the weeds. I looked at large magnum pistol primers and thought.....well they are real close to the same size, and the pressure of my load is in the area of 12k CUP, according to the book and QuickLoad seems to agree.....and that is well under what a magnum pistol pressures would be, so I closed my eyes and hoped for the best. No issue, and looked like a pretty clean burn, easy to tell in a trapdoor, everything is right there to see. FPS numbers right there as well, so for that year I used the mag pistol primers.
Some of the things I have read on going under book specs is the....well that load is ok in 25acp so it should be ok in 45-70, ahh do the case volumes have anything in common.....don't think so.
In the end the last discussion on the pistol powders ended up in a dog pile and the thread locked.
So with all that said, you do you, but I sure as hell ain't gonna do it, my rifle will sit before I do that.