A friend has several French revolvers marked 1873 St.Entienne..they were orginally a 11 mm.With a very small amount of boreing, He has bored them out to 45 cal.He has slugged the barrel to confirm the cal.
Problem is they were orginally black powder. What smokless
powder will approximate the pressures of a 45 cal 45 cal.
What powder to use and source of supply?

Lots of people here have more experience than I, but, if it was made for blackpowder, stay with black powder or the new Clean Shot or Pyrodex or some of the other "new" black powder replacements. None of these are smokeless.

These guns would have been made when heat treating of steel was non-existent. Load smokeless in them, there is a high likelyhood you will be picking pieces of them out of your anatomy. If you shoot these pieces at all stick to black powder!
Mark

I firmly agree with the posts above, if you use anything but black in them you are begging for trouble, it's not that it may burst the cylinder, it will, and harming all those around, those old guns made back then, particularly those made in europe, were made more of iron than steel.
I'm forever telling people that "black is an explosive, modern is a propellant" its like putting nitro in your car, if it's old it will blow to bits. besides what's wrong with black powder anyway? Paladin

Have only looked at a couple of 11mm French revolvers, never fired one. Have worked with a 10.4Italian and a couple of .450 BullDog types...on a guess, the French was actually better finished, but don't believe it would be any stronger. Won't say a smokless load couldn't be made to work, but will say that it's not going to be easy to stay within acceptable pressure. Personally, I'd stay with black or RS Pyrodex.

Fiocchi still loads the 10.4 and the .450, and perhaps a lesson from them would help. Both are smokless loads...the powder isn't a match for anything seen commercially. The bullets are made with minimal bearing area, are smaller in diameter than the bore of the examples I've measured (and yes...they shoot pretty poorly), and are light for their caliber. Those are "tricks" to keep pressure low.

If you "just gotta" then keep the above in mind: small diameter, short bearing area, low weight help keep presure down (also keeps smokeless from bruning worth a rat's rump, but that's the idea). The above pretty well describes a round ball; a good place to start with BP as well.

BP gun!! Use only BP in it -unless you don't like your face/hands!!! Nuff Said. :(