Yep, definitely try modifying the bolt catch before the lower. The bolt catch rubbing against the hammer is not an issue. When the last round is fired, the hammer will be already cocked upon the extraction. More than likely, it's the bolt catch and its retaining pin that's the culprit. Take the roll pin out and see if the bolt catch binds in its slot using a smaller punch tool as a placeholder. If it's fine, then you may have to open up the roll pin hole in the bolt catch. With my M1S kit, I had to use a small drill bit to increase the hole diameter just enough to not bind on the roll pin.