Optimal Bbl. length for cast in 223 & 308 ?

[Wayne S]

Basically I have two choices for either Cal. 20" or 26". It would seam that with the reduced powder charges used with cast the optimal length would be 20" as the powder should have burned by the end of the 20" and anything longer would just be drag and actually be a bad thing ?? The intended use will be 200 Yd. small steel plate plinking

[runfiverun]

if you are gonna just use light charges the 20" bbl will be fine.
if you want to push things with the 223 a longer bbl will help drop muzzle pressure for a better [less stress] boolit exit.

[Harter66]

I saw an story several yrs ago that involved a 30-06' 10,000 rnd of ball ammo and a bbl shortening experiment. The velocities climbed w/each 1" cut from 30"to 24" . 23 an 24" were dead even. @2" showed a little jump at 21" there was another drop velocities dropped from there.

Based on the above I would hazard a guess that the 20" bbls will be plenty. Unless you intend to to use ridiculously slow powders in both little would be gained if anything w/longer bbls .

[popper]

40 gr. H4895 under a 165GC'd from a 18" 308 bbl doesn't leave any unburned powder.

[HangFireW8]

Just a technical point... all the powder that's going to burn is burnt well before 20" or even 18"... the question (regarding velocity, anyway) is, has the resulting pressure dropped below the 4-6K PSI required to continue accelerating the boolit by the end of the barrel? That is more a function of the quantity of powder loaded, of course, it is usually safer to load a larger quantity of slow powder than fast.

High pressure muzzle blasts are not just inefficient regarding velocity, they catch up to the projectile after muzzle exit and can destabilize the projectile slightly, resulting in lower accuracy.

With jacketed bullets in 308, 20" is rather optimal, not that a 22" won't give you a little more velocity, but with a heavy barrel it gives you a very stiff, low vibration barrel that still maintains standard sporter weight balance and carrying characteristics. Twenty inches in 308Win was all the rage in police sniper rifles just a few years ago, any operator type with a longer barrel was definitely out of fashion!