All of Les Baer's upper receivers require fitting to your lower. You would be extemely lucky to get one and have it work without filing on it. They are made this way on purpose. I have done this a few times myself and do not ssee any benefit to getting a Baer upper if there is a Bushnmaster or Eagle Arms upper to be had. Mine (3) required alot of filing along the bottom edge of the upper and also some in the take down pin holes. Too much for me to want to do it again. I did it one time to a SGW lower that seemd to be a little out of spec. I was able to fit a Baer upper to it and it runs great. I just can't swap out the upper to anything else. I did it two other times to make a custom 9mm upper. Baer does offer thier uppers with or without forward assists, dustcovers. The fitting is alot of effort for something that I don't think is really needed unless you have a problem with your lower.