I used to get a lot of them brought in for repair when I owned a gun shop (in the 70s, while they were in production). The problems stemmed from poor quality parts and manufacturing, rather than under powered ammo. In fact, the most frequent problems were broken firing pins and broken toggle arms - more powerful ammo would have broken those parts even faster. They looked neat, but were completely unreliable. Cheap cast parts, poor tolerances and a lack of quality control were the culprits. I worked on one my brother had for a long time in an attempt to get it to work reliably, and finally gave up, the basic components were just too bad, and pot metal castings don't respond well to machining. They had a poor reputation when they were new, age hasn't improved them. Too bad, they would have sold like hot cakes if they had been decently made and reliable guns.