I'm planning to build a caplock rifle now BECAUSE of the over-regulation of bp. None of the replica powders will work reliably in a flintlock, so if I'm going to continue to shoot a muzzle loader I'll need something that works with the available propellants. It'll be a shame to hang all our beautiful flintlocks up for display only, but I can see that day coming... sooner rather than later.
Food for thought:
Don't know how old you are or how much you shoot...but when I switched from caplocks to Flintlocks years ago, I had several pounds of Pyrodex RS left over from a Walmart ewnd of year sale at $8/pound.
I found that duplex loads...what I call 'layered loads'...work perfectly in a Flintlock.
My smallest powder measure happended to be 20grns, so I'd use a 20grn igniter charge of Goex 3F downbore first, followed by 30/40/50grns RS that I wanted to shoot that particular day...100% consistent, reliable, accurate, etc...used up all those pounds of RS in my Flintlocks at the range.
If you put up a case of Goex 3F as igniter charges, that's almost 9000 shots...and if make a smaller measure and just use a 15grn igniter charge that's almost 12,000 shots in a Flintlock...2 cases in your house, 2 cases at a relative's house, etc...you get the idea...you can keep right on shooting Flintlocks...and for me, if I'm going to shoot muzzleloaders year round, I'm going to shoot Flintlocks and the igniter charge approach works perfectly.