I have a CMMG M4LE upper that I obtained on a group buy direct from CMMG years ago. It has all the 22ARC upgrades: SS bolt and collar, anti jam charger and the forward assist adapter. I also have another upper which I built myself with the same upgrades. They have both been in my safe for several years and have not been fired. I recently pulled them out and noticed a problem with both of them, I cannot pull the bolt back without it binding and hanging up in the receiver. I have tried this on different lowers and also on both uppers alone by holding pressure on the back of bolt and pulling on the charger, The bolt hangs up every time and gets stuck. I have attributed this to the forward assist adapter device. When I remove the device, both uppers operate properly. My forward assist adapter is an older design that is solid on top. I noticed that the newer ones show a window cut in the top. Looks like a design change? I know that they are installed correctly. I contacted CMMG via there website but have not heard from them yet. Anyone have any ideas what is wrong here?