It doesn’t matter what the “jacketed spec bullet” diameter is, what matters is the actual bore diameter of the OP’s barrel. Not all barrels are the exact correct bore size, many are at least slightly larger. Example, many .44 Magnum rifle barrels measure 0.432”. Too, in Microgroove barrels many find better accuracy sizing up two thousandths - what brand barrel does the OP have? The OP needs to slug his barrel to be sure. Or he can just shoot any size bullet he wants, and never know if the poor accuracy is due to a too small bullet, too high velocity, the wrong powder or something else.
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