Are you measuring the land to land or groove to groove? That sounds a lot more like groove to groove and you don't want anything that big. Use the smallest measure you can on thescraped in areasget (as long as the rifle has an even number of lands/grooves). Odd numbers get a little trickier and require a bit of math aside from the measuring.

You want to order no more than about .001 over land to land - in pure lead. And you'll want his #2 lube. Anything more than that size and you'll need a short-starter. Might as well get into the ease of slip-fit stuff.

Assuming your measure is true, rounding itup to .512 for groove to groove and assuming a .004" to .005" rifling depth - your land to land should be .502 to .504. Rifling depth could even be more so don't make any assumptions there.