What gun is this?

I believe it is an AirForce with a Custom Maddog stock.

It certainly looks like it is based on one of the Air Force guns, with such a short body it could possibly be based on the Talon Pistol. Hard to really tell the scale from pictures, Neil.

Looks like a Maddog stock
And I am pretty sure this is an Airforce rifle. I have seen that rifle before, not sure where

NM the stock in your picture looks a lot longer, that is why I thought it might be based on the pistol, the body of the gun looks pretty short for one of the rifles, but pictures are always deceiving, Neil.

Looks a lot like this
http://www.armslist.com/posts/4189325/fort-collins-colorado-air-guns-for-sale--air-force-talon-p-

Definitely a talon, notice the smaller tank in tin boats pic. That is the talonp tank(pistol). Of course you can swap spin lock tanks and/or barrels for lots of different combos.

Same gun as this, just different bolt on package.