semi-smokeless v. smokeless powder

Does anyone know of a loading reference which compares the pressures of the semi-smokless powders shotgun powders produced from the mid 1890's through the 1930 and standard smokeless powder. From what I've found semi-smokeless powder was basically smokeless powder with about 5% blackpowder.
The reason I ask is because I have my great grandfather's Belgian , 12 ga double. It has Belgian semi-smokeless proofs, "fluid steel" barrels.
Apparently my great grandfather originally used black powder rounds on advise of the gunsmith that sold him the gun new, and did so up until they were no longer available locally about the mid 1930's. My dad recalls being with his grandfather when the local gunsmith told him that he could no longer supply blackpowder rounds. The gunsmith recommended the use of "low brass" commerical one ounce loads of 3 dram equ. (ie,.Remington Shur Shot)The old man took the smiths' advice and thereafter did all his rabbit and bird hunting with that load .
The gun was passed to my dad & uncles , and now that they're all gone, it's my safe. I've never shot it much simply because it's just to darn long (32" barrels). From the old family photo's I've seen you could probably fill a box car with all the pheasant, rabbits and ducks taken with it. More than just couple of foxes never made it to the henhouse,
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. I HAVE NO INTENTION OF RELOADING FOR IT! THANKS

Elmer Keith in his autobiography speaks of using King's Semi Smokeless. I belive it was a bulky powder that filled the case.

I can't cite a source, but I have read ads & articles about "Cowboy Action Shooting" loads made with BP and perhaps low pressure smokeless. Also,, Briley or another shotgun barrel maker will line barrels of old guns like yours which then can be used with smokeless loads.

A "fluid-steel" barrel is a modern design barrel. Should be fine with modern light hunting loads. Have a good shotgun 'smith look over this shotgun. I think it will be Ok with modern light hunting loads.

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Originally Posted by Calif-Steve

A "fluid-steel" barrel is a modern design barrel. Should be fine with modern light hunting loads. Have a good shotgun 'smith look over this shotgun. I think it will be Ok with modern light hunting loads.

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According to an article in the American Rifleman several years back, semi-smokeless powder showed up about 1894. We have a photo of my great grandfather, dated OCT 1900, holding the gun in question (pheasant hunting). This is one of those common , "run of the mill" Belgian made '"farmers' guns". Has an interesting lockup which appears to be a double dog leg/Greener combination. It's still nice and tight.
As previously noted, my family has put cases & cases of modern, smokeless light loads through it since the mid 1930's. Besides the "fluid steel" stamp there's also the Royal Damascus mark, which is nothing more than a printed pattern on the barrel.
Has the common "Wm. Moore" name, trying to make believe that it's a high end English piece.

All common shotshells, from the earliest blackpowder loads to the latest you'll find on the shelf today are loaded to a limited range of peak pressure - generally between 6,000 and 11,000 psi. The problem with some vintage guns originally made for black (or semi-smokeless) powder is that they were designed to contain these pressures only in the first few inches of the barrel, not farther from the breech. The finer grades were often prized for having light, thin barrels that gave them superb handling characteristics for upland bird shooting. While thin barrels were fine with the quick-burning black, semi-, and most early smokeless powders, they are more likely to fail when used with modern progressive-burning powders that may produce the same pressure but sustain it longer - and therefore farther from the relatively thick barrel walls near the breech.

Since we seldom see pressure figures or powder specs on factory-loaded shotshells, it's not usually possible to know for sure if they will be OK in a vintage gun. The solution is careful handloading, selecting loads that use relatively quick powders (Red Dot, 700X, etc.) and are listed by the powder manufacturer with peak pressures at the low end of the spectrum.

Here's one example from Alliant's website -

(2 3/4" WW-AA hull)

Shot Wt.(ounces) - Velocity(fps) - Primer - Powder - Wad - Grains - Approx. psi

1 1/8 - 1,090 - Win 209 - Red Dot - CB 1100 - 16 - 8,000

The same powder charge, but with 7/8 oz. of shot and an appropriate wad, will give about 1150 fps at around 7,000 psi and does the job at skeet or 16-yard trap when pointed right.

Handloads in this class are less likely to damage vintage shotguns than are loads of unknown pressure characteristics or handloads with slower powders and/or higher peak pressure.

Semi-smokeless powder was a mechanical mixture of mostly black powder and a fairly small proportion of nitrocellulose. It was useful because it could be loaded bulk-for-bulk with black and had similar ballistic properties but left significantly less fouling in the bore.

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Originally Posted by kcw

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.

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Sorry for bringing this old, dead thread back to life [ZOMBIESZZZ! ARRRGGHH... :lol:] 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.