I have a 10ML2 and shoot smokeless in it, and youre exactly right, the higher pressure cause the breech plug hole to get bigger and then you get blow back and finally lack of ignition. They recommend you change the vent liner every 100 shots. Randy
Wakeman sells some extended ware vent liner, that he claims is 2x. I change mine every year and don't worry about it no matter how many shots I shoot (not over 100, but over 20). The Savage vent liner is well designed, and I know that size of the flash hole is important in ignition in Smokeless, so that is going to go over to BlackHorn, since it is so close to smokeless. So in my mind, any breech plug that will shoot Blackhorn consistently over hundreds of shots. Plain old BP or pyrodex, I don't think it matters, but with BH or Smokeless size of hole is big deal.

I like the flat breech plugs since the convave ones leave power in the hole and it sometimes is difficult to get out if your shoot a lot and you got soot in there.
Chap