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AndyC wrote:As you said, it's subjective - that's one reason you tailor-make your ammo to suit your preferences.

And that's a great point. It amazes me how a caliber that may be marginal or otherwise suboptimal in the form that it commonly takes can be made into a great set of compromises with a few small tweaks. The corollary is the question: why are some calibers so badly misused by the people who should want to maximize them and should be the best at doing so?

Of course there are tradeoffs, but my point is that some are subjective. How desirable is efficiency? How awful is muzzle blast?

I was considering the K&M m17s, and the choice between a 16 or 20" bbl .308 vs a 17.5" bbl .300 Blackout forced me to think through these issues more carefully than I had in the past. For a group that carries guns around, the broad form of that question seemed interesting.

Thanks for the replies.

I have a crazy habit that I'd like to share and get thoughts on. When I consider a cartridge, I think of the barrel as part of the cartridge. For an extreme example, consider a .300 Winchester Magnum with a 30" barrel vs the same cartridge with a 6"barrel. One is unthinkablly short, the other is a touch longer than the norm but still within reason. Why? If we think of the brass case AND barrel as the same pressure vessel, the the expansion ratio for the powder gas generated by the combustion of the powder renders much of the powder wasted for a short barrel.

As a counter example, a 6" barrel .357 magnum is quite reasonable while a 30" barrel would be actually lose velocity vs, say, an 18" barrel due to losses from friction.

We are really constructing a pressure curve, with the max pressure set by the case strength and the length of time that our pressure differential is allowed to act upon the bullet set by barrel length. These are non-linear relationships, but higher values CAN lead to more muzzle energy. Mismatched, they can lead to a needlessly long gun or a gratuitous muzzle blast. Remember, powder gases exit the muzzle moving faster than the bullet and function almost identically to a rocket engine vs your shoulder or wrist.

Presuming that shorter length is desirable, as are high muzzle energy, low muzzle blast and low recoil, then certain features become more desirable. In trying to maximize the good and minimize the bad, higher pressure and a well matched barrel length becomes truly desirable. Further, when a short barrel is needed, a smaller caliber may be a better choice than a more powerful one.

By way of example, I love shooting my P226 X5 .357 Sig with a 5.7" threaded barrel. It is not a carry gun. Instead, I use a P232 stainless in .380 ACP. I find that a .380 is well matched to a 3.5" barrel and my recoil tolerance. Those are very different guns, but similar in that the barrel lengths are matched to cartridges for ballistic efficiency. In rifles, the new SBR craze has resulted in similar debates if more forgiving limits. Is a .308 with a 16" barrel an eardrum shattering masochist's weapon or a reasonable way to move the same .30 cal 150 grain bullet 500 fps faster than a .300 blackout of similar overall length?

What about a 24" vs a 28" magnum rifle barrel? Why do butt stocks get a free pass for chewing up inches of overall length?

Anyway, I'm interested to hear thoughts.