On the range I got the best results with the 46 gr Winchester Hornet HP's in my rifle. I shot these loads side by side with factory ammo for slight elevation change and better group. The 45 Hornady flat nose "Bee" bullet was a close second for accuracy followed by the factory 40 gr HP. Results with factory HP's on prairie dogs was in a word "impressive". Groups were in the 1 1/2 - 2 inch range and may be improved when I float the barrel and glass the action. In any case, at reasonable distances - you won't miss a p-dog because of the group size at 150 yds. Single loading using a 40 gr V-max may be the "go to" bullet for a little better trajectory. I also cast bullets and may try loading 55 gr FNGC's if the bullet shank and nose length prove compatible. FWIW the serial # on my rifle is about 20 off of the rifle Shooting Times used in their article (under 100). It took me almost a year on backorder before I got it. So it is "early production".
Many people ask "what is it good for ?" or what to know if it will go through a level 2 or 3 vest. I don't have any reason to test the penetration on vests. It is "FUN" to shoot. I just tell them it's like a "reloadable .22 Mag".
As far as magazines go - YES, Para P-18 mags can be made to work as long as you don't mind spending an hour to reshape the feed lips with a needle file and cut the mag spring down. Is it worth it? Probably not. I got my other mags from ASW and didn't look back.
Will I use it more? - Oh yeah. Will I work on load data? Yes. In a couple weeks I should have some more rounds down range and be able to give a little more data. When I let somone handle the pistol they usually comment on the trigger pull. Only change I made (so far) - I swapped the factory spring out for a 9lb Wilson spring. Ejection pattern is at 4 o'clock and less than 3 ft from me. Factory was at 5-5:30 and closer to 4 feet.