760 upgrades?

Flat top piston and valve

Yup definitely flat top piston and valve. Also port the exhaust on the valve at an angle, enlarge it slightly, install a larger diameter T-port and oval port the barrel. Installing an aluminum barrel band is a great upgrade although it won't give you any more juice it makes the gun feel so much better. Here is a link to help.

http://thegreencrosmanforum.proboards.com/thread/75/more-piston-valve

polish the ports. flat top valve/piston

Mine was rebuilt and 625 (10 pumps ) fps with BB's is the norm. I don't like doing it but I can get 650 fps with 12 pumps. round 550 fps with 7.5gr Crosman and 10 pumps. Not souped up but terminal for rats at 10 yards.

Here is a review of the 1000fps Legacy 1000 (some say an upgraded 760)

https://youtu.be/cj5C6HMyBq4

You could probably hunt with it. 

RADEN1942;

I have a 1974 pre-July Powermaster 760. Traded for it 23 years ago. Used it for a few weeks then into the closet. Pulled it out a few months back and have been messing with it since. By messing I mean rebuilding it to specs...learned how from the internet (decent internet wasn't around 23 years ago) Rebuilt it put out 657 FPS avg. (10 rounds) and reasonably accurate for not being rifled but I get approx. 25 FPS increase in velocity when I've managed to keep the breech plugged by my temporary fixes.

A problem I discovered however, was a pretty bad air leak right where the brass bolt enters the breech (where the BB's/pellets are pushed in the barrel. This only happened when fired though. Every time I shot the thing my eyebrows would twitch. I've tried all kinds of fixes that would only last 1-3 rounds before they blew out, blew off or disintegrated. So I'm trying one last thing involving surgical rubber tubing (the really soft pliable stuff). I'm going to try it tomorrow. 

I'm only on the forum now because I posted a request at the front of this sub-forum for anything that might come close to a permanent fix. I realized that the leak was fixed on later versions of the 760 by Crosman wrapping the breech bolt in rubber. This took up the space around the bolt and it blocked the air leak, ergo my attempt at a fix involving surgical tubing. The problem is choosing the correct diameter tubing inside and out. If you're interested I'll post my results tomorrow or the next day. Who knows, maybe someone will answer my post with something that works.

BruceJ (Biznawich)