16ga.com ~ View topic - Down-barrel pressures for low pressure smokeless powders

Joined: 26 Apr 2010 Posts: 3177 Location: NCWa

I was reading a chapter on double rifles that were designed prior to smokeless powder. According to the author since blackpowder is basically an explosion and the pressure is immediate and then as the space increases due to the bullet/shot moving through the barrel, the pressure decreases. Because of the initial jolt of pressure, the breech, chamber and first few inches of the barrel were heavily constructed but since the pressure rapidly declined, the portion of the barrel from the fore end to muzzle was significantly less structured.

Using shells loaded with progressive powders would result in pressure much more constant as the bullet/shot moved through the barrel. While the pressure may be entirely within the strength limits of the breech end of the gun, it may exceed the guns design near the muzzle.

To those that are knowledgeable of Damascus and other barrels designed for use with blackpowder, is this a real world or a theoretical issue?

Actually AmericanMeet according to the data produced by Sherman Bell, there is very little difference between the rise and "taper-off" of pressure between black and smokeless. It happens for the same reasons -- fairly quick release of energy and drop off of pressures as the projectile moves down the barrel, increasing the volume. There is very little systematic difference, if any, in the down bore wall profiles of shotgun barrels intended for black vs. smokeless.

Also, never imagine that all smokeless powder has the same burn rate or "brisance" (look that up in your Funk & Wagnalls!). As you might know there are several different "grinds" of black, which equate to different surface areas, and therefore different "burn rates". And the various manufacturers have different formulations of black, as well. That's why it is almost comical to see the advice that damascus barrels are safe for black powder only, when black powders can have some of the same ranges of brisance as smokeless, and that's what often matters. Also the fact that black powder is considered an explosive vs. a "fuel" as in the case of smokeless, causes some misconceptions about what happens in a gun.

Remember, the big deal about cautions of avoiding smokeless in damascus was about those who hand-loaded black powder in it's necessarily high volumes. Some early smokeless users did not understand the energy concentrations in smokeless powders and were accustomed to loading by volumes of black -- for instance, for a lot of loading they used the same volumes of powder (black) as shot! Powder is powder, right? . . . NOT! And the world's reserves of stupidity and ignorance are not decreasing, either, are they. So loading by the familiar and accustomed volumes of black is totally nuts to you and I, who were weaned on smokeless, isn't it. Well, people were doing that and breaking guns, so the manufacturers decided to write off the "old technology" entirely so they could sell new-tech ammo (smokeless -- clean bores, less corrosion), and also, damascus barrels were old tech and more costly to produce than new "fluid steel" barrels, so the industry, wanting to sell the new "safer" (yes, marginally perhaps) guns, wanted to paint the "old technology" in it's darkest terms. Lawyers and liability problems are not new things.

Cheers!

Joined: 28 Aug 2014 Posts: 924 Location: Eastern Tennessee

Interesting this kind of conversation came up in the last day. Just this morning I was musing the lack of black powder loads I have for the 16 gauge. Can't say I am looking make loads for everyday use, but thought the trap kids would get a kick out of one of my old toys leaving a massive cloud of dust in the wake.

Charlie , those smaller , old Hodgdons loading books used to have a small section of BP loads .

Joined: 21 May 2010 Posts: 603 Location: Victoria BC Canada

google-up "Pteryplegia". Old, but stands the test of time.

Better; Try this; "Black Powder Shotgun Basics - spectrum". A four page article that sums it all up. The original is a bit arcane.

home.insightbb.com/~bspen/shotgun.html

P.S. My University library has an electronic copy, which I will look up as originals and copies are not cheap.

Scroll down to the bottom here for several pressure curves
https://docs.google.com/document/d/1F2sQuPm05IE4VWYYnCkvuXmYEzQoWd_SQgaAfUOZEFU/edit

Not much difference between the older Bulk Smokeless (DuPont and Schultze) and FFFg. Ballistite was Dense Smokeless and DuPont Oval the original Progressive Burning Smokeless.

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The curves essentially meet at about 3 1/2" - just past the forcing cone where, because the taper of the cone is more acute than the external barrel taper, the wall thickness is actually greater than the end of the chamber

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