Interesting. not familiar with "tap loading" I see the hole, do you drop the pellet head first and the little butterfly knob feeds it?
This is a "Winchester-badged" Diana 50 from about the 1970's. Try Google-ing that gun and you'll find a wealth of info. It's true that the velocity is not real high (generally thought to be due to extra dead space in the tap loader) but highly accurate and with internals the same as Diana's Model 35 at the time.Don R.