This is a semi-auto conversion of an older Sheridan pump gun.  These are converted by Palmer's Pursuit Shop, and are amazing.  I highly recommend looking into there work. 

Here is all the information on this particular Stroker as I use it to play.

Palmer's Stroker number P782

1.    Right feed fixed barrel, brass tubes with short porting.
2.    Worr games inline regulator.
3.    VL2000 (pre-revolution.
4.    TASCO mini-mag red dot sight
5.    Drop forward and bottom line.
6.    20oz anti-siphon tank.

This gun is amazingly stable with the CO2 and the reg.  +/- 2 fps in the summer.  Not bad for a gun this old.

Here is the history of this particular gun.

She was born in March of 1994. Originally she was a PMI-1 DF (direct feed).
She was sent in to Palmers in July 1994 for a repair to the feed nipple.
August 1999 was the time for a 4-way replacement.
I bought her in December of 1999 and sent her to Craig Palmer in January of 2000 for porting of the barrel and trigger lightening, and some other miscellaneous stuff.
Now in Oregon at Punishers Custom.   This gun now is owned by Ian Scott