SG ammo currently has the Federal version of the 158grn LSWCHP +P "FBI Load" in stock for $16.95 per box. While the Federal version isn't loaded quite as warm as the Remington one (Federal, Winchester, Remington, and Buffalo Bore all make a version of the "FBI Load") it would probably still go plenty fast enough to expand from a 4" barrel and $17/box is about what FMJ or LRN range ammo is going for at Wally World these days.
http://www.sgammo.com