Actually, the main reason for the "reliability" of the AK-47 has to do with the cartridge it uses. The 7.62X39 has a much more pronounced taper compared to say the 5.56X45. This makes it much easier to load cartridges and eject spent casings.. ..
If that's the case, why does the 5.56x39 in the AK-74 have the same reliability? That case doesn't seem to be overly tapered.
Everything I've even seen or heard said the reason the AK was reliable was because of the loose tlerances. That is also the reason for the loose accuracy.
Either way, in the real world the piston actions are LESS reliable than a correctly made gas gun.
The 7.62X39 has a body taper with a an agle of 1.2 degrees, this is almost three times as much taper as the 5.56X45 which has a body tape of 0.47 degrees. The 5.45X39 has a body taper of 0.72 degrees which is quite a lot more than the 5.56X45. The 7.62X51 is the straightest of the bunch with a taper of 0.35 degrees. (I sure hope I got my trig right.)
You can have loose tolerances all you want but, the issue of reliability has to do with getting cartridges in and pulling fired cases out and shorter cones go in and out a lot easier than longer rods.
As for your final statement that only applies to piston Vs jet ARs. A rifle designed from the ground up to be piston-powered can be extremely reliable. In the case of the AR, the piston is an afterthought that negates many of the design advantages of the rifle.
