So my friends got a cetme clone he wants to sell, its a century arms sportster. And when i was looking up issues with them it said the big thing to look for is bolt gap and it needed to be between .5 -.7mm. My only question is how to measure it? My understanding was to cock it back into safe and then give it a hk slap and let it slam forward. He says this is bad on it and doesn't want me to do it. So is that the proper way to get the gap or what? I don't want to buy it if its out of spec. Also what do you guys think is a fair price for a gun like that? Its not perfect. There are some nicks and use marks. Hes claimed to put 300 rds through it.