Biggest difference I saw was the older had a flat face most likely for pellets vs. the one for BH209 was dished out which I assumed designed for loose powder. You're supposed to use full bore 209A primers, not the ones specifically for black powder and/or substitutes. Never had any kind of delayed ignition with BH209 and a Fed 209A primer.

BH likes a hot/standard 209 primer as opposed to cooler ml primers for pyrodex. Yes open the hole in the breach plug a little.

I have been in to ML hunting for the last couple years
My go to the the Blackhorn 209 with 94 measured grains

I have a small scale, weigh the empty tubes first and take out the ones with a variance
And zero the scale
Then weigh 94 grains of Blackhorn.

I use an accurate 240 grain bullet. And i cannot find the details on the bullet! Will post when i can
But it is two shots almost connecting holes at 100yards 1.5 inches high

94gr by weight is stout !!! I've been shooting 72gr by wt with a 290gr boredriver and recoil is pretty wicked