I have a 9mm upper which I will be using on an ar 15 lower with a 9mm magwell conversion block (colt style). I'm using a 9mm bolt which was ramped by ADCO. My buttstock is a Rock River Arms tactical car stock (non-collapsible) fixed length. This comes with the same spring and buffer used in an A1/A2 buttstock. According to RRA's conversion info I need to use a stock spacer, 9mm buffer and car action spring see below:

http://www.rockriverarms.com/popup.cfm?type=t&id=4

I want to know what would happen or not happen if I just use the spring and buffer the buttstock came with?

Thanks,

Frank

My guess, incorrect mass for the blowback operation of 9mm. You end up damaging or causing increased wear on the rifle if the mass is to low.