Here's an excerpt from some private correspondance from a friend of mine who is in the ammunition business and pressure tests alot of stuff.
Played with some TB 45-70 loads and my concern level is not as high as it was, although I still think is has no place in firearms intended for black powder pressures only. If, A VERY BIG IF, you do not load any more than the available powder space left in the cartridge, WITHOUT ANY COMPRESSION, it is pretty hard to get much beyond 30KSI. Another "IF", someone keeps stuffing it in until they get actual balckpowder velocities, I think the results would be much closer to disaster. I will do those tests when I have time. A friend sent me some 420 grain brand x (terminally, they sucked) bullets to check pressures using some RE10 (he could no longer find his favorite RE7 locally). After the test, I had some left over plus some others I got from Montana Cast. Now I only had enough gel left to fire a few shots so I need to set aside one days worth of gel to a solely TB test but this is what I got. With the 420 bullet, there was room left in the case 16.3 grains to the base of the seated bullet. I started with their 70% rule and the result was 921 fps @ 25,100psi. About what I expected. Next I filled the entire space with 16.3 grains of TB and on firing two shots, the result on the first was 1059 fps @ 26,700psi. The second shot was 1100fps @ 30,600 psi. Not very consistent but not exactly a hand grenade either. Next was a 500 grain bullet. I forget the exact brand/model but it was more of a Sharps style round nose that had most of the bullet outside the case, i.e., not a lever gun bullet. The room left under the bullet held 17.5 grains. I loaded that amount and the result was 1012 fps @ 29,500 psi. Like I said, I still think it is the wrong powder for black powder pressure guns (76s, trap doors, etc) but in modern rifles, my blood pressure has come done some so I guess I will lay off those that choose to use it for mouse fart loads in Marlins, Shilohs, and Miroku 86 replicas, etc.
