Larry;
I have made that statement in the past about hanging a gun on the wall if it was not considered safe with 8K loads, so I am likely the one you recall saying it. An exception to this would be a gun with light a breech section built prior to the introduction of smokeless. IF in a good sound condition I would consider shooting it with Black Powder Only. Also, I have stated on numerous occasions that the rise in pressure down the rest of the barrel is only a "Slight" increase. It is not normally enough to be concerned about. The fact remains though & is really beyond dispute, that using a load with a low chamber pressure when the same shot charge is given the same velocity, does Absolutely nothing to help the forward end of the barrel.
Glad my memory isn't failing. Seems we agree that there just isn't a lot of point to working up loads that are much lower pressure than that as far as safety is concerned.
But I remain interested in determining just how much advantage a high pressure load offers vs low pressure in terms of retained pressure at various points further down the barrel. Thought I recalled that Sherman Bell gave some examples of that in one of his "Finding Out For Myself" articles in Double Gun Journal, and found it in my files. It's Part VI, "Smokeless vs. Black", Summer 2002. In that article, Bell's goal was to repeat what we see in the Dupont tests from the 30's, comparing smokeless to black--but using modern smokeless powders. But in running those tests, he provides some data on retained pressure down the barrel. He placed strain gauges at 1, 3, 6, 9, and 12 inches. Fired 10 shots with each load he tested to get an average. All of his loads were low pressure--nothing over 7,000 psi--but there's enough difference between the lowest and highest pressure loads he tested to make an interesting comparison.
He tested two comparable loads, one using 7625 at a one inch pressure of 4800 psi; the other a black powder load at 4700 psi. At 12 inches, the pressure from both was 1800 psi. He also compared a load using Universal Clays that read 6900 psi at one inch, along with a black powder load at 5900 psi. 12 inch pressure of the Clays load was 2000 psi; the black powder load, 2100 psi.
While the two higher pressure loads shed more pressure in 12" than did the two lower pressure loads, they still retained slightly higher pressure at 12". So we're not seeing any gain yet, at that point. It's too bad he didn't use any higher pressure loads. Undoubtedly a 10,000 psi load would drop in pressure even more over 12" than any of those lower pressure loads. But it also has a lot further to drop before it catches up with them.
So at what point down the barrel does the higher pressure load drop below the pressure of the lower pressure load? The graph from the Dupont test shows that the loads with the highest and the lowest peak pressures have flip-flopped at 3", with the lowest becoming the highest, and the highest dropping to the lowest. That doesn't happen in Bell's test. The two low pressure loads (black and smokeless, respectively) have dropped to 3700 and 3800 psi at 3", while the two higher pressure loads (again, black and smokeless respectively) are at 4700 and 5100. Low pressure loads are 2400 and 2300 at 9"; high pressure, 2900 and 2700. But the loads in Bell's test are not "twins" to the same degree they were in the Dupont test, where they were all 3 dram equivalent, 1 1/4 oz shot--which likely makes a difference. Likewise, Bell's use of modern smokeless powders may also be a factor.
It would be interesting to run the same test with all modern smokeless loads, same shot charge, same velocity, but with widely different peak pressures. Would the results look more like the Dupont graph, or more like Bell's results? It would certainly be a good subject for yet another "finding out for myself" series of tests.
Last edited by L. Brown; 06/21/19 12:25 PM.
