I second the O-ring idea as mine has them and they do help. I have no pics as everytime I save enough for a camera I end up buying a knife instead! Every AR I've handled in the past 5 years, a total of four, has had excellent fit, finish is not as high as a CRK, but it is not intended to be so, also have had excellent lock up. I've never had the SNG, PT, or the larger one, name escapes at the moment, but I do know the AR/GB series, and they are GREAT!!!
SMF is the one I could not think of.