A couple days ago I started working on an Rhop mod for my SVD and as I was firing it I noticed the bbs would drop out of the barrel at like 50 feet. So I chronoed it at 100 fps with .36 which is very low (normally 300 fps with .36). So I think maybe I just need to file down the rubber more. I do and nothing changes. So then I put in my original bucking (with no rhop) and chrono. It reads 170 fps with .36 (hopup turned off). I relubricate all parts and refire. same thing. I remember a long while ago I would teflon tape the cylinder head to increase fps so I inspected it. There are deep scratches going from the rear of the cylinder head to the front. I believe this to be the cause of air escaping. Any thoughts on how to fix this because no replacement parts are available. I havent tried teflon taping it yet. I know this is the cause (90% sure). I own JB Weld maybe apply some into the grooves and then sand it to be flush with the outer diameter? Any thoughts?