I owned a 600 for a number of years (plus a number of vintage air rifles/pistols) which I recently sold, as I'm shooting more powder burning pistols now!
The 600 was only made for two years, 1969 - 70 if I recall. Crosman spent a lot of time building the 600 as they are quite complex, and probably more time repairing them under warranty, as they are "finiky", causing to Crosman stop production!
The pistol holds 10 .22 pellets and as the OP mentioned it shoots in true semi automatic mode, not like most of todays repeating pistols, which are basically SA/DA revolvers within a semi auto pistol look a like enclosure.
The 600 will not operate well, or at all using domed Diabolo pellets (which I think are in the tin shown in the photo), the domed heads will interlock and this will cause the loading gate to jam up. Flat head target pellets will feed much better. Crosman produced some horrible .22 flat nosed pellets when this gun was made and they created a lot of the FTF issues customers complained about. I fed mine with RWS Meisterkugeln .22 flat nose pellets, but other flat nosed will feed well.
As the semi auto mechanism is operated using the C02 powerlet, the 600's just devour C02 gas, I would get 25 - 30 rounds maximum per powerlet.
Great little C02 pistol, fairly accurate, you'll have a blast shooting it, thanks for sharing.