"IF" one is Concerned about a set of barrels with good wall thickness at the breech end but thin at 18+ inches from the breech, shoot the load which gives the highest breech pressure commensurate with the overall desired ballistics.
You may for instance shoot two 1 oz loads which both reach 1200 fps muzzle velocity. If one of those loads has 3K "Less" "MAX Chamber Pressure" than the other, it's going to make it up some where else. I TRULY WONDER just where that might Be.
Miller, can you show us test graphs or point to references showing pressure rises from chamber to muzzle that illustrate your point regarding your statement about identical muzzle speeds and loads, lower pressures, etc. ? Thanks. Gil
Note in the chart which Drew posted how the curves all cross between 3"-4" at which point the low pressure becomes the high pressure load & Vice-Versa. "IF" you push the same shot load to the same velocity you have done the same amount of work. That work in a shotgun barrel is accomplished by pressure. Thus if you lower it at one point you raise it somewhere else.
Now that said the "Peak" pressure occurs for a very short distance & extremely short time while the raised portion is spread out over virtually the rest of the barrel. in either case the pressure down the barrel is much lower than the max/peak pressure which occurs in the chamber.
Bottom line though is if you keep the same load & just change powders to drop the peak pressure you have not made it a bit easier on the gun other than directly in the chamber. These low pressure loads are actually most beneficial if you have a gun with very light breeches having thin walls over the chamber & particularly the junction of chamber & cone. In most guns this is not the case, particularly those built after the introduction of smokeless when this area was generally Beefed Up.
