Caliber

A&K make a gas powered underlever 1892 model Winchester (i.e. the cliche John Wayne cowboy rifle), which you can easily find for about 140 quid if you look around, there is a two tone available, as well as a full wood and metal one. It has a mag capacity of 30, which is twice what the real thing had.

Note that it is pretty hot BTW, firing at about 400-450 fps with .20 BBs, so you ain't gonna be using it for indoor CQB, but most external sites would class it as a sniper rifle anyway because it's a single shot lever action, so effectively similar to a bolt action sniper rifle. It is pretty accurate at long range though, so it could indeed be used to snipe.

Thanks for the info, Chock. Only 140 and it's gas, sounds like a bargain to me.