The 3 screws on the top and the one on the bottom were just nipped up on mine when the barrel was changed, i put them back the same - just nipped up. The barrel is quite a tight fit anyway so you definitely don't need to go crazy.

more power - more muzzle flip, also flat heads start to loose their accuracy beyond about 20m and don't particularly like it beyond about 650fps. Done a bit of work on this for BR on an HFT500 and that's what i found.

have you tried it with Jsb heavies 10.34? Was almost 1.1ft/lbs higher than 8.44's on mine

i've got a s200 barrel on my hft500. It was turned down and is free floated and is brilliant. From memory they start off life 15mm (?) so should turn down onto your rifle i would have thought. Good luck.

TX200hc mk3 .177 for sale, Tony Leach conversion, very good condition. £425 (prefer not to post but may be willing to meet up subject to discussion, based Southampton area)