Wayne Van Zwoll fired alot (1000's) of rounds to determine optimal barrel length for many cartridges. It checks out pretty close to me for the rounds I have used.
Mr. Van Zwoll did well with this one. Out of the cartridges that I have used except one, this was spot on. I would disagree a little on the 25-06, my experience is the 26" is better with the heavier bullets & a couple of the newer powders, noticeably so. Anyway, good stuff.
"Well respected shooter Wayne Van Zwoll reported his recomendations for barrel length as follows (seems to be directly determined by case capacity/velocity potential etc.) This is directly from the book "Hunter's Guide to Long Range Shooting"
20" barrels: 30-30, 32 Spl., .35 Rem.
22" barrels: .222, .223, .250 sav., .300 sav., 308 win., .450 Marlin
23" barrels: .243, .257 Roberts, 7x57, .260 rem., 7mm-08, .35 Whelen
24" barrels: .22-250, .220 Swift, 6mm rem., .270 win., .280 rem., .30-06, 338-06, .358 Norma
25" barrels: 25-06 rem., 7mm rem., 7mm weatherby, .300 win., .300 H&H, .308 Norma, .338 win.
26" barrels:257 weatherby, .264 win, 7mm RUM, .300weatherby, .300 RUM.
He then goes on to state that he'd list new Short Mags, with the belted magnums whoes performance they match. He also states the The mightiest of high-velocity cartridges would take the longest barrel you can conveniently carry. (his book gives numerous velocity charts for several different calibers with barrels that get cut down inch by inch)
These numbers come from years of testing and experience. Obviously different applications would require different barrel lenghts but interesting information regardless. If your shooting very light bullets for a specific caliber you'd be using more powder and could therefore use a longer barrel to increase velocity by a great deal."