Quote Originally Posted by kcw View Post
I'm just curious as to whether there was a substantial pressure differance between semi-smokeless and smokeless rounds. Morever I can't understand why semi-smokeless powder was even ever used in the first place.
Sorry for bringing this old, dead thread back to life [ZOMBIESZZZ! ARRRGGHH... ] but stumbled across it while looking for info on the transition from BP to smokeless myself and thought I'd answer this.

Prior to the advent of non-corrosive primers, BP residues diluted & carried away a lot of the corrosive priming salts, so semi-smokeless had some "best of both worlds" attributes: you didn't have to stop shooting to clean BP fouling mid-string, & were condemned to cleaning your firearm immediately after use regardless, and true smokeless was more expensive than BP [my, how that has changed!]

As to pressure concerns, I just read that Annie Oakley preferred Schultze powder over black in the period prior to the invention of true smokeless. Accroding to one contemporary report, Schultze was rated at approximately 3x the power of BP by charge weight [but was apparently much bulkier, so you ended up w/ only slightly more power when equivalent volumes were utilized.]

True smokeless powders [by Vielle, Nobel, Abel] were both MUCH faster burning than BP and produced much higher pressures and more dense, making it impossible to load by volume in the old BP manner.

Also, early smokeless powders were notorious for various negative attributes. One of the worst of these was running hot & "burning barrels" [this was one of the downsides that led to abandoning the 6mm Lee Navy, fwiw.] So until smokeless powder manufacture matured in product consistency, etc. and primer formulations changed, semi-smokeless had a lot going for it.