Crosman SSP250
This was a rather large CO2 single-shot pistol produced by Crosman in the mid-90's. It was offered in .177 caliber, but also had two other barrel options (.20 & .22) available separately. The USA version has two power levels...525fps and 560 fps. I've used Crosman's #1399 shoulder stock and an inexpensive Crosman 4X scope to make a handy carbine. This particular gun is .177 and has taken it's fair share of small varmints using Crow Magnum pellets.