was doing some interesting searching and found this.
Burn rate and Barrel length - Shooters Forum
243 barrel length vs powder - Page 2 - Long Range Hunting Online Magazine
While perusing this forum I found a comment by
Rocky Raab that seemed to debunk my assumtion that faster burn rate powders would perform best in shorter barrels(and vise versa) for a given cartridge. Upon some more searching I found this nugget from
Unclenick that sums it up very nicely. It seemed like it should be brought out into the light a little more in a separate thread. The amount of knowledge shown here on this forum is amazing. Thanks to all those who take the time to share!
"On barrel length: Depending on the powder, in typical rifles peak pressure occurs when the bullet has moved somewhere between one and three inches down the bore. Just before reaching that peak, the initially ignited powder will switch over frôm progressive to digressive burning, at which time the remaining burning powder mass is around 20% or so. That number combines the tiny digressively burning pieces with the powder thrown forward with the bullet that never got started burning very well in the first place (the stuff that burns when you put a match to floor sweepings at an indoor range; not recommending you do that, btw—lead hazard). It burns in ever decreasing temperature and pressure, so it doesn't contribute much to velocity. Once the bullet has got maybe five or six inches down the barrel, you could stop burning the rest and would still get to about the same muzzle velocity as if you'd left it burning.
The result of the above is, until you get down to a barrel length under around five or six inches, the same powder that produces the most velocity in a long barrel will also produce the most velocity in a shorter barrel. Period. So, be clear that if you move to a faster powder for, say, a 16" as opposed to a 24" barrel, you are doing it to reduce muzzle blast and recoil. That can help accuracy, so it is often a good idea frôm that standpoint, but it will come with a velocity penalty."