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I've been watching this thread and am puzzeled. How can you discuss useful barrel lengths and twists without specifying the bullets you're trying to shoot? A 600 grain cast lead Postell certianly doesn't need the same barrel length or twiist as an 800 Grain Barnes solid. The bullet style also determies what length of action is needed and the shape of the throat.
For supersonic bullets barrel length determines how much velocity you can squeeze out of given case capacity and peak pressure. But for suppressed subsonics you just need a barrel long enough to allow the cartridge to get the bullet up to speed. Any longer just hurts accuracy from velocity dispersion. Typically 8 to 12 inches is plenty. For legal reasons a lot of subsonic barrels are 16 inch. For unsuppressed rifles a long barrel can reduce muzzle pressure to where the propellant gas escapes the muzzle subsonic, which makes the rifle fairly quiet, but then barrel friction becomes a major issue.L Lubricated cast lead is the usual solution. I have subsoinic rifles with barrel lengths from 10 to 36 inches. They each have their place but not for all bullets. For twist rate you have the choice of selecting a barrel which shoots one style bullet very well or any bullet with only fair accuracy. It's unlikely to find one barrel which works right for all bullets.
Maybe another thread on selecting bullets for subsoniic use would be useful . The target and it's terminal ballistics mainly controls bullet selection. Range and atmosphere also play a part. The name of the cartridge or it's diameter and powder capacity (like stating it's a 510 Whisper) have much less to do with selecting barrel length and twist than does bullet selection.
Last edited by LouBoyd; 11-24-2008 at 09:08 PM.
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