you might want to verify, but I don't think the 18.5 off of a 510 will fit a 500 or vice versa. The distance from the breach to the barrel nut isn't the same. As a matter of fact, here is the measurement from my 510 so you can check your 500 and see. With the barrel installed, the distance from the front of the receiver to the barrel nut is 9 and 7/8 inches