I suspect that with even significantly more than 500 rounds you'd have nothing to worry about.
As to price, It sounds like you did ok in my humble opinion (I'm no expert). Looking at their web site, new piston uppers retail for more than what you paid. In this market, half the battle is finding one at all, at any price.
MSgt, USAF, Retired
NRA Life Member
The hardest thing to explain is the glaringly evident which everybody had decided not to see. - Ayn Rand
Last edited by Overkill0084; 03-02-2013 at 02:37 PM.