Let's get one thing straight first -- the optimum twist rate is based on the LENGTH of the bullet, not its weight. A heavy round-nose bullet requires as much stabilization as a much lighter VLD bullet that's the same length. It's a matter of how long a longitudinal axis has something spinning around it -- not how much weight is spinning around it.
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<br>The only 75-grain .224 bullet I've checked is the Hornady A-Max boat-tail with polycarbonate tip. I recorded its length but don't remember it. The Greenhill equation calls for a twist of one turn in 6.9 (call it 7) inches, which is too short for good results at the velocities this bullet can easily reach from the .220 Howell (or even the Swift). An 8-inch twist would be better, but my barrel-maker assures me that his barrels with a 9-inch twist will stabilize this bullet, so that's what I have in both my .220 Howell rifles. We'll see whether he's right.
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<br>Rechambering a Remington .22-.250 or .220 Swift barrel to my .220 Howell is a good and workable idea ONLY if you load the .220 Howell with no bullet longer than the usual .22-.250 and .220 Swift bullets -- nothing, IOW, heavier than 55 or maybe 60 grains. It'll shoot 'em faster, of course, but they'll also lose velocity faster than the heavier, lower-BC 75-grain A-Max. The 75-grain will yaw, wobble, and tumble in that slower twist -- just how badly, I can't guess and won't waste money to learn.
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<br>A friend of mine near here is trying to make some other fellow's .220 Howell shoot and not having much luck with the original longer twist in that rechambered barrel.
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<br>A new barrel from Day One is the money-saving way to go. A 9-inch twist may indeed be the best, but an 8-inch twist is more sure to be adequate.
