Back in the day, Dad bought a Webley .455 for 17.00 at Montgomery Wards, a Moisan Rifle for uner $20, and an SMLE for under $20 which came with 100 rounds of .303 tracer ammo and a Weaver .22 scope shipped by mistake. All surplus rifles and ammo. Then came the Gun Control Act.....
I've had lots of surplus guns over the past 50 years, all interesting but not all what anyone would call "Great". First thought - be sure you can get ammo, then BUY IT. Second thought - extra magazines are sometimes hard to find and pricey, BUY at least TWO extra magazines. Third thought - before you take something apart, be certain you know how to put it back together. Only take things apart INSIDE the house the first time. Flying springs take other parts with them and hide in grass (personal experience). Fourth thought - Military ( and some civilian) ammo names and metric designations SOUND SIMILAR and interchangeable. Often they are not.
I inherited several hundred rounds of WWII surplus 9mm Parabellum ammo many years ago with odd markings on the bases. Wow! Some countries have/had submachinegun ammo and pistol ammo (not the same). Thought five -beware of surplus ammo loaded with corrosive primers. They will eat your bore if left uncleaned long enough.