#1. There is no specification that any Large Frame AR manufacturer must follow - unlike AR15s. AR15s havae the M16/M4 TDP to follow, which are .gov specifications, so most AR15 manufacturers rarely fuk it up. There's a pattern for them to follow.
Not so with Large Frame ARs. Different manufacturers can do whatever they want, when they want, make any spec that they feel is proper - and sell their own guns.
#2. There are 2 distinct gas systems. AR15 gas systems, and Armalite AR-10 gas systems. There's a few major differences between the two systems, and the aftermarket has muddied those waters. The gas tubes are different lengths, between those two systems. The aftermarket though it would be good to "make and in-between" which works like shiit. Their (aftermarket) mentality is - if the gas tubes are a different length, let's just drill the barrel gas port in-between those standards, and it won't matter what gas tube the customer gets..."
And nothing could be further from the truth. Those "engineers" need fired, and they need to be moving into a cheaper apartment soon. They're idiots.
So, that's it, in a nutshell.