All of this, and more, are already variations you need to take into consideration when assembling an AR. Commercial buffer tube vs. milspec; a zillion and one different kinds of gas blocks; not to mention the huge variation in buffers and buffer weights.
Different designs and options is not the same as no parts compatibility... in fact, you kind of make my point... all those options, and they all fit/attach to the same upper and lower receiver no matter who made them.
But there are standardized dimensions. The gas block on a standard Ar barrel is .75 and yes there are variations for bull barrel, and for larger calibers.
Point is, a .75 gas block is standardized, the bull barrel size is standardized...
What would happen if DPMS made barrels with .7 gas blocks, Colt with .725, Daniels .76, BCM .78... etc etc
There may be Mil spec buffer tubes and civilian buffer tubes... but the threads that allow you to attach it to the receiver... they are the same on both.
The barrel extension size is the same on all ARs based around the 5.56 variant dimensions, no matter the caliber it is chambered in.
What variation we have on the AR has been driven by the need to sidestep legislation... Things like Colt large pin receivers...
There's probably more variation from one AR to another than there is between a Tanfoglio 9mm, a Sphinx AT2000 and a CZ 75B.
There is a surprising amount of difference between a Tangfolio and a CZ... very little parts compatibility.
To continue the auto analogy, we don't expect parts for a small-block Ford to fit a small-block Chevy, so why should Colt 1911 parts fit a Kimber 1911?
Because those are entirely different designs... Same end result but with different design paths to get there...
Its the same as a 1911 and Glock 17 are different designs, but achieve the same goal... a locked breech semi auto pistol. You could even throw in different methods to lock the breech... or throw in a blowback into the fray... either way, you end up with a semi auto pistol, but different ways to get there.
What would be bad... is if a custom engine maker, made parts available to the public, claiming to be Chevy 350 small block Blah blah... and then they not fit on the Chevy 350 small block blah blah you have sitting in your garage.
Or say the parts on a chevy model XYZ made in California, don't fit a Chevy XYZ made in a licensed facility in Mexico or anywhere.
Some parts require hand fitting regardless of what the seller of the parts claims.
The 1911 isn't quite as standardized as the AR, and parts fitting is indeed a thing that often needs done.
Most that buy aftermarket parts are looking to improve something, usually accuracy, so making parts fit a little tight and need fitting aids in achieving this goal.
The M1911A1 was standardized; the S&W or Kimber or Wilson copy was not, and no government inspectors make sure of parts interchangeability.
True... but the manufacturers know that one of the major reasons to own a 1911 is the ability to customize it, aided by a large availability of aftermarket parts. They also know the areas these parts focus on... So they attempt to keep those areas close to the original specs.
Its not so much that it is expected that you can completely disassemble pistols from , Kimber, Springfield, Colt, etc... throw the parts into a box, shake em up, and then randomly grab parts and build three functioning pistols again.
Its more akin to... We expect the deign to conform to a standardized spec and design closely enough that we can pick and choose custom parts that will work with minor fitting.
That parts will more or less be in the same place and work the same... ad that the design will not be altered so radically that major components are in essence completely different designs.
They expect, for example... That the magwell will be the same size and the mag catch will be located in the same spot and work the same way, so that any brand magazine will fit.
The 1911 isn't perfectly standardized between manufacturers, but the basic design and specs are close enough in line that on the whole, getting aftermarket parts is not an exercise in massive frustration.
In the case of the AK, there is quite a bit of variation between makers and models, and most parts do require fitting, not wholly unlike the 1911.
Yet the AK design is popular and appears to be gaining on popularity.
I will point to my above statement about avoiding legislation...
People also don't expect parts from an AK made in country A, by company B, to go inline with an AK made in country C by company D.
They do expect parts claiming to be for a certain model work for that model.
Also, Aks tend to be customised much less functionally... But things like the trigger and bolt do tend to stay the same regardless of other differences. The side rail on the receiver used to mount optics, is expected to work with any accessories designed for the rail, no matter who made the rail or accessories.
And I think their popularity is driven by fad like causes, the AK reputation, and the cheapness of the platform... Not the desire to build up a highly custom gun. Most changes tend to the cosmetic... Highly custom guns tend to be made as whole rifles. most I see are attempts to make them more modern and compatible with modern sights/scopes/accessories, most which are designed with the AR in mind.
