Doc White is a true gentleman. Yesterday I sent him an e-mail posing the question. He replied this morning.
Here's his reply.
LAND TO LAND SHOULD BE .430, GROOVES .035 DEEP, NO DEEPER THAN .040, TWIST
FOR THE 250 GR BULLET 1-32, NO FASTER THAN 1-28 FOR A 300 GR BULLET, hOWARD
KELLY IS YOUR BEST BET, AT WEBERTOWN RIFLEWORKS, ON THE NET. doc