You need a hacksaw, a tennis ball and some lapping/grinding compound.
Cut it as square as possible then use the ball and abrasive compound to re-crown.
Or get a crowning cutter from Brownells.
Not that big a deal.
"I am old, sick, and tired of living. If you feel the need to mess with me, go right ahead." My Uncle, with his hand on his pistol, talking to a troublemaker. 2-13-1935 -- 2-1-2013