One major issue is that most jams are not caused by the gun, per se, but by a magazine. If the mag spring gets worn out, it may not have the next round there "in time" for the slide when it comes forward. If the feed lips are bent or a bad fit for the particular cartridge, the round won't be oriented correctly during feeding.
Most guns that have been selected for military use, agency use, and/or for use by very large law enforcement departments have usually been subjected to a mean-rounds-between-stoppages test. As others have noted, variations in technique, ammunition, and care make it impractical to expect a weapon to never, ever, ever jam. But if the ammo and shooter are consistent, and mags are in-spec, it is quite possible to have an extremely reliable autoloader. Not counting issues with one (aftermarket) magazine that had bad geometry, I have shot thousands of rounds through my Browning BDM without a single jam.
Most guns that have been selected for military use, agency use, and/or for use by very large law enforcement departments have usually been subjected to a mean-rounds-between-stoppages test. As others have noted, variations in technique, ammunition, and care make it impractical to expect a weapon to never, ever, ever jam. But if the ammo and shooter are consistent, and mags are in-spec, it is quite possible to have an extremely reliable autoloader. Not counting issues with one (aftermarket) magazine that had bad geometry, I have shot thousands of rounds through my Browning BDM without a single jam.