About the only Semi Auto airgun that might fill the bill is the Crosman 600. They can be finicky to get set up for the pellets you want to shoot, and some of the more critical parts are unavailable except from guys parting out others.
They sell for a bit of coin, too. Expect to spend $300 or so on a decent one plus the parts and seals it likely needs. You will do well if you get one running for less.
Fun units when operating well, but...
I sold mine a few years back.
Crosman single shots are about what the market has in it these days, without breaking the bank. In used, there are a few revolvers that can be tuned up, in particular, the Crosman 38T in .22. The early models with the all brass valve, and the direct impingement hammer (no transfer bar) were able to be tuned and adjusted to put out useable power as well as accuracy.
Lots of 'semi-auto' looking .177s that are actually revolvers internally, lots of single shot guns, very few true semi auto airguns around. You can spend up to a couple $K on a match grade semi auto, still in .177 cal, but it still is sketchy as a grouse gun.
Essentially, you are looking for something that is not there these days.
Look hard at the aftermarket conversions to .25 cal or even larger. Move a bigger projectile at under 500 fps, and you get more energy at the target. Think in terms of whether you would wish to be hit by a baseball or a ping pong ball, at equal speeds. It's about the energy you can get to the target.
Best of luck.
Cheers
Trev
