Minimum accurate velocity of PRB

[Gaze]

I was playing with a calculator that claims to measure recoil. It is sensitive to bullet velocity.

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[CoyoteJoe]

At 25yds about any load that will get the ball there will probably by accurate enough. 50 is more demanding of a smoothbore and 75 to 100 gets real demanding. Just ballance your need of power against your tolerance for recoil and you'll probably find accuracy OK out to 50 yards.
I believe those recoil calculations are a good representation of actual recoil impulse but the gun and stock design have such a great effect on "felt recoil" that the numbers are meaningful only when comparing near identical guns. Even small details like the exact shape and position of cheekpiece can make a gun pleasant for one shooter and nasty to another. :imo: