I'm running the OSS 7.62 Suppressor on my Scar 17s and I don't get any gas blowback with this suppressor, but it is normal for the chamber to be dirtier when shooting suppressed. I have started using TW25B grease on the bolt carrier group instead of oil. I did this simply because the bolt carrier group on the 17s is pretty heavy and has a lot of contact areas, not because I'm shooting suppressed. The TW25B grease stays put really well and I think it helps prevent some friction. I don't have to re-oil it every time now. One thing I do for cleaning the chamber is take a couple metal cleaning rods and screw them together so it is long enough to reach the chamber when inserted from the rear of the rifle. Put your chamber brush on one end and tighten the other end into the chuck on a cordless drill. Now you have a 3,000 rpm cleaning tool! Then change out your chamber brush for an attachment that can hold cotton cloths and clean up the mess. I can get my chamber super clean with this method. Hope this helps.