all floating and barrel was chambered for 223 wylde. I assume wilson blank. I purchased from RR and torqued barrel and tube to upper myself. I have armor tools . I have digital torq wrench. I believe that I used 50 lbs of torq. I had barrel on a flat top upper but experienced the same. I want to use flat top for other options like a 16 " barrel that I also ordered from RR. I hope to use this old style if it will do job. I have a NF scope that I will try next range trip. I hate working up 52 grain loads with 400-500 brand new 69 smk bullets staring it me. If what I have read is accurate and the barrel is not too heavy for upper, then it makes sense that scope mt or itself is culprit. It is just a little more effort to remove NF from my Browning and sight it on the AR and then take it back off and resight it on Browning. I DO NOT LIKE THE RECOIL that the 300 Browning does to my shoulder.