I just picked up a new Bushmaster Retro-Fit Gas Piston Kit. I had picked it up with the intention to put it in my AR but l changed my mind on it and I am going to stick with the impingement system. I am familiar with it more and my other AR's have the same set-up so I don't want to fool with it. I still have the receipt for it and I picked it up at cost so that is all I would like to get back, the total was $370. Would be willing to trade or sell. Thanks