MD
90gr 3f T7 is to hot for the black diamond? give me a break! even my traditions rates 3f much higher than that.
Maybe if you knew more about what you might be talking about you could understand.
It is not the rating of the rifle that is the problem, you can shoot 120 grain of T7 in the barrel if you like. But again it is not the rating.... it the amount blow-bac pressure coming back through the nipple - that is what is casuing the problem. He could shoot a light 200 grain bullet and probably would not have a problem at all as the bullet would move easier and farther up the barrel increasing bore volume.
Most any of the older open breech type rifles were meant to shoot with a number 11 or a Musket cap. The advent of the 209 made a lot manufactures add that type of ignition to their list of accessories. Even the Bighorn, which is rated at 150 grains of T7 will blowback the primer and hammer when shooting a 209.
T7-3f which is much finer than 2f and thought to be 10% stronger than 2f so therefore 25% stronger than any of the Pyro's creates a problem in the older guns that try to use a 209 ignition.
T7-3f ignites and reaches peak pressure much faster than 2f in fact so fast the ability of the bore to increase the volume of gas it can contain, especially when shooting a 300 grain bullet is hampered. The pressure has to go someplace and the easiest place to go is back out the nipple - hence the blow-bac and even the pushing the hammer back to the firing position.
The TC Black Diamond is a very good old technology gun and will probably work just fine with 100 grains of T7-2f or any of the slower buring less pressure creating Pyros.
Hope this makes some sense to those that understand.
and I think Cayugad also suggested a new nipple -
mitchmtm1 your current 209 nipple might be eroded. Have you looked at the hammer spring, BP residue can eat a spring fairly easily if it has not been cleaned well and it might be a bit weak.
I had the same problem in my White U-mag when shooting 100 grains of BH-209 from it. The primer blew out of the nipple, pushed the hammer back and reputered the primer- i found the anvil on the floor of the breech.