Re: Barrel length and powder burn rates?
In looking through my reference library to try and prove 'your' supposition, I happened upon a couple paragraphs from Julian S. Hatcher, whom certainly should need no introduction.
From pages 309-312 of "Hatchers Notebook" (pages 310-311 are pictures only), he discusses burning rates and methods to slow burning to extend the pressure as the bullet proceeds down the barrel. The following is quoted, any typos are certainly mine. I've highlighted portions that are directly relevant to our discussion.
" The great trouble with getting high velocity in a gun is the fact that when the powder in the cartridge is ignited it turns into gas, and this gas, confined in the small space of the cartridge case, creates a very high pressure which pushes the bullet along the bore of the gun. But as soon as the bullet starts to move along the bore, that leaves more space for the gas to occupy, hence there is less pressure, and the effect of the powder will rapidly fall off to nothing unless special means are taken to keep the pressure up.
One of these special means is the perforation of the powder grain, which causes it to have a larger burning surface as the combustion proceeds. This is because the primer flash ignites the inside of the tube as well as the outside of the grain. As the grain burns, the outside surface gets smaller, hence the rate of evolution of gas would burn away, and the diameter of the hole becomes larger, with a corresponding increase in the interior burning surface.
The balance between these two surfaces can be controlled by the ratio of the inside diameter to the outside diameter in the finished grain of powder. In cannon powders with their larger grains, there are usually seven perforations instead of one.
Another method of controlling the burning of the powder and making it more progressive, that is, making it holdup its pressure longer during the travel of the bullet, is by coating the powder with a substance which makes it burn slowly at first. As this coating burns off the outside of the powder, the speed of combustion increases. These progressive-burning powders tend to give a more uniformly distributed pressure, sustained longer during the travel of the bullet. Moreover, the maximum pressure is not so high because instead of being exerted all at once, the pressure is spread out more evenly during the entire travel of the bullet. The du Pont "Improved Military Rifle" powders such as I. M. R. No 3031, I. M. R. No. 4320 and I. M. R. No. 4064 are progressive powders.
Like black powder, smokeless powders are also controlled as to their speed of burning by the grain size. Powders with very fine grains burn up in a hurry and therefore are particularly suited for short-barrel weapons. Powders with very large grains take longer to burn up, and are adapted to long-barrel weapons such as cannon. ..."
The text continues to talk about granule size and ignition dynamics, but is not directly relevant to our current discussion.
I'll sit here on the same page as Julian S. Hatcher, I also suspect that Powley is sitting here beside us.
If some is good and more is better, then too much is just right.
My mind is a raging torrent, flooded with rivulets of thought, cascading into a waterfall of creative alternatives