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Several black and smokeless pressure curves can be found in the links.

12g Black Powder peak pressures are only slightly lower than many modern smokeless loads
1 1/8 oz. 3 Drams (1200 fps) of DuPont FFFg (82 grains) is about 5000 psi.
1 1/8 oz. 3 Drams Curtis & Harvey�s No. 4 T.S. (82 grains; somewhat similar but not equivalent to medium grain FFg) was about 6500 psi.
1 1/4 oz. 3 1/4 Drams Curtis & Harvey�s No. 4 T.S. was about 8500 psi.
Black Powder substitute pressures from the 2001 �Lyman Black Powder Handbook & Loading Manual�
1 1/8 oz. with 100 gr. GOEX FFg at 1200 fps = 4,800 psi
1 1/8 oz. with 100 gr. Pyrodex RS at 1200 fps = 5,600 psi

Thanks for the good advice.

But, I am reluctant to use smokeless powder--and I have seen a number of 3f period loads (I can also use 3f in my Trapdoor Springfield).

Maybe once I gain familiarity with a light BP load---and am comfortable with the comparability of smokeless.

And, I am impressed by the The Double Gun �Finding Out For Myself� series by Sherman Bell.

Black Powder does not GO OFF all at once. Back in 1970 I built a .32 cal Squirrel Long rifle. It had a slow round ball twist. When loading it light for squirrel there would be a spot in the barrel which was extremely fouled, preventing loading another ball without cleaning. Increasing the charge moved it toward the muzzle, but it took a real heavy charge to move it all the way out the muzzle. Black powder was slower burning than available smokeless powders until the development of the "Progressive" powders used in the new high velocity/heavy shot charge shells which appeared in the 1920's.

It does not "go off" all at once, but it does so a heckuva lot faster than smokeless. Want to see for yourself? Take an 8 ft. long 1 x 6 and pour as thin a line of smokeless on it as you can for the entire length ........... maybe 3/8" to 1/2" wide and 7 ft. long. Do this outside where there are no other combustibles. Now, light the end of the string of smokeless and see how long it takes it to burn. Then, turn the board over and pour an equivalent size line of black powder down the board's length. Now, light the end of it and stand back. The black will burn to the other end so fast you can't follow it with your eyes.


We used to do this as part of a m/l rifle demonstration for hunting clubs and other interested groups. No, it doesn't burn all at once, but it is lightning quick. Detcord doesn't burn all at once either, but it does burn at about 6400 meters/second. Let that sink in a bit.

SRH

Stan;
With all due respect that is not a true test of the burning rate of black vs smokeless when confined inside a gun barrel. One characteristic of black is it burns at essentially the same rate under "All" conditions, smokeless does not. Its ease of ignition & the ability to burn unconfined are the reasons for its restrictions in shipping, storage etc. Black is slower burning than powders such as Unique, PB etc & anything faster.

I can accept that, Miller. Thanks for the clarification.

But, I do think many people who are unfamiliar with black have the opinion it burns much slower than it does. It is relative, to what one considers slow. I guess I have shot so much of it in my life that maybe it seems to burn faster than it does. All this silliness that some go on about it going off like a hangfire every time is just that, silliness. I am aware of no lagtime in the ignition of a black load and a smokeless one. Maybe in the lock time, but the difference in actual ignition is imperceptible. Furthermore, a well tuned flintlock's ignition is almost imperceptibly slower than a percussion's, to me. But then, maybe I have a poor perception of the passing of time. That reference to DetCord is a good illustration as to how poorly I perceive short intervals of time. We used to blow beaver houses and dams occasionally with Detagel, an explosive that looks like a little sleeve of ground sausage, but white. We'd plant several charges at various spots along the length of a dam and connect them with Detcord, then run a measured length of slow burning fuse to the first charge. When the slow burning fuse got to the first charge they all seemed to go off simultaneously, because of the speed of burning of the Detcord. There was no perceptible time between explosions. Same for me with black vs smokeless.

SRH

The only issue, aside from cleaning, that black powder loads introduce over RST low pressure smokless is increased recoil effect on old stocks.
Sufficient lube keeps fouling soft for many shots. We shoot BP trap using cartridge blocks so we can put a dab of Crisco lube on the mouth of each cartridge.

I don't understand that statement Saskbooknut. If a load of smokeless, RST or otherwise, with the same shot payload, leaves the muzzle at the same speed as the blackpowder load, the recoil will be the same. The only possible difference could be the weight of the gases, which is negligible.

SRH

1931 "Smokeless Shotgun Powders: Their Development, Composition and Ballistic Characteristics" by Wallace H Coxe. NOTE: "All powders loaded to develop the same energy" (ie. the area underneath each curve) Curve includes "Progressive Burning" DuPont Oval & FFg



1927 with FFFg