Picked up a couple of cans of Pyrodex labled for rifle, I'm assuming muzzle loader. Would like to try useing it for fixed ammo in my Stevens 44 1/2 model 45. in 25-21. Any suggestions as to how much powder to use.        ...MIKE...

What was your bad experience? Been using it for years in front loaders and have used it in cartridges with no issues. Just have to clean it like you would with black powder. I prefer 777 over the original but both work fine. I find it to be less corrosive than black but it is still corrosive.

Tried Pyrodex in several BPCLR rifles, mostly .45-70, and had terrible accuracy.  Okeh up to 100 yards but after that black is best.  FWIW.

I shot Pyrodex for a couple of years in a .50 cal Hawken M/L I had and the accuracy was as good as black in that rifle. Pyrodex is loaded on a volume for volume basis with black, not on a weight basis. As an example in the Hawken 85 gr of 2F gave a M/V of 1800 fps, it only took 66 gr of Pyrodex to get the same M/V.  66 gr of Pyrodex filled the powder measure to the same level as the black.  The other problem with Pyrodex is that it's useless in a flintlock rifle, probably owing to its higher flashpoint.  The main advantage I found with using it was that the barrel fouling did not accumulate during shooting so you don't have to clean between shots, but you must clean the rifle thoroughly after use.
Mike.