Ok here goes
There is no PC Thompson gun, since the only evil features are a pistol grip and detachable mag.
If you buy a 1927-A1 you can use stick or drum mags. If you buy the M1 Thompson you can`t use the drum mags, because originally the M1 Thompson was never supposed to.
As far as reliablity goes make sure that you only run 230grain Ball FACTORY ammo, anything else won`t work. I stress factory because I`ve tried some reloads and the gun didn`t cycle that well.
For durablity don`t get the lightweight models, I`ve heard that the receivers wear out prematurely. Stick to the heavier Thompsons. Your only problems should be little things mine were loctiting the rear site on my M1, and a new firing pin retaining pin on my 1927A1.
CDNN has 30rd mags for $14.99.
A word on stick mags, the original hole is round for the FA Thompsons, where as the SA Thompsons you have to enlarge that hole into an oval. I really don`t know why they did this.
Try autoordnance.com