Cousin Pat said:
wow - not sure I understand some of the terms you used, but interesting stuff. My conclusion is that barrel length > about 15" out to 24" lead to a 5% velocity LOSS = about a 10% muzzle energy loss. Thus these longer barrels are a negative not a positive in pistol calibers. Am I thinking about this correctly? thanks - tom
QuickLoad is a program that calculates internal ballistics. Pressure, velocity, all kinds of "stuff".
The precision it gives with straight-walled cartridges like 45LC is a little iffy but the basic concept is certainly correct. It might be at 14" or 17", but somewhere in there the velocity starts to go down.
From a pure velocity/energy perspective a long barrel is worse than a shorter barrel. There might be other considerations though, such as the mentioned sight radius. Accuracy trumps power, every time.
skizzums said:
can anyone tell why this is the case? seems to be the opposite with rifles, although i rarely have seen ballstics on barrel length over 24in
Modern, high-power rifle cartridges typically have much greater case capacities, operate at much higher pressures and have much smaller expansion ratios. Expansion ratio is basically the amount of space the powder gases have to fill as the bullet moves forward. Because of those factors, the powder continues to burn and produce/maintain pressure in much longer barrels.
Even rifles will start to lose velocity eventually though. For example, a 55gr 5.556NATO round can get to about 3,135fps in 16", up to 3,431 in 24" but gains only another 120 at 30", for 3,550, and only another 60 at 35". By 40", it's losing speed.
PathFinder said:
What I found was the faster burning powders like Red-Dot or W-231 would gain about 200 fps in the longer barreled rifle; while the slower burning propellants like 4227 would gain 400 fps.
Generally speaking, whatever powder produces the fastest velocity in a long barrel will also produce the fastest velocity in a short barrel. There's a point where this is no longer true, depending on the specifics. Within reason, say going from 24" to 20" or even 16" in most cases, whatever was fastest at 24" will also be fastest at 16.
Going from short towards long, you'll find what you mention, that at some length (usually that would be considered very long for a handgun but much too short for a rifle, 10 or 12" , or so) the fast powder will be over-taken by the slow one. For every length up from there, the slower powder will be better velocity.