What he said
can be true for a 22LR... a new fancy long-barreled one with really old ammo maybe. But complete BS for a centerfire magnum
Even the 22LR blurb is somewhat BS because old 22LRs (and even new match ones) are meant to be subsonic. And it's not all that hard to stick a subsonic in a barrel, I've done it in 9mm before. Thankfully never in a 300 BLK. But the goal in match 22LR is to stay subsonic because what's the point of shoving a heeled lead cone that's just a glorified ball supersonic and having it go nuts falling trans and sub sonic. Hypersonic 22LR rounds work great for shooting squirrels and armadillos and little critters at 25 yards, but in the 22 match world you want to start and stay sub-sonic. So there's really no need for very long barrels past a point because you don't even WANT them to go faster. Odds of sticking a 22LR are in the slim-to-none range because almost no one hand loads for them. I only know of a select few nut jobs in the rimfire ELR game that mess around with the Cutting Edge kits. Seems awesome, but I can buy a 500 round brick of Lapua and be perfectly happy at a much lower cost.
Back on topic. He's wrong. Any reasonable loading of a 6.5 PRC will gain velocity with more barrel length. There are tradeoffs for the added velocity gain with longer barrels in weight increase and the hassle of carrying a javelin through woods, but nothing in the 20-26" range is going to matter all that much. Longer barrels will be slightly faster, but if that small change in velocity is super duper critical just step up to a 7PRC or 300 PRC and get all that energy back - and then some.
There is absolutely nothing wrong with a 24" barrel, there's nothing wrong with a 20" barrel or a 26" barrel. Pick the one that fits what you want to do with the rifle, and be confident that it doesn't matter a whit unless you're trying to do very marginal things with it. I like long barrels so I shoot long barrels. But I also shoot very short barreled bolt action pistols now too, thanks to
@Ernie getting me hooked on the XP platform.
If so what's the advantage of a 26in barrel? I see 24in is far more common.
About 30-75 FPS and nothing else. If it's a sporter metal barrel maybe more muzzle diameter to thread off of on the 24". Maybe slightly more rigid depending on the barrel taper. 22" is where some of the really light contour sporters max out at, but with so many carbon fiber barrels around now it's somewhat rare to see a pencil barrel on anything but a low-end model rifle.
Maybe those last few inches are where the leprechaun that makes PRCs and Creedmoor's shoot so well lives, I don't know
