Great article detailing some of the many, Many, MANY issue involved in tuning the AR family. Large or small, they can get ... complicated.
I wandered off the beaten path a few times myself, with 7" barreled 5.56 AR15s, and .300 Whisper 16" versions. Change bore diameter, change gas port size or location, change bullet weight, change powder, change buffer weight, change spring, change buffer tube length, barrel length, etc, etc, and you can get into unexplored territory, where experimentation is your only guide, and real world results are discovered the hard way.
STONER got it close to right with the ORIGINAL AR10 ... aka BIG CHASSIS AR ... which balances gas power, buffer weight, bolt carrier weight, gas volume and pressure, etc, specifically for the 7.62 NATO cartridge ... which is basically standardized for gas port pressure and bullet weight, wherever it is made.
The Dutch made the original Stoner AR10 design even better with their military issue FULL AUTO versions for the Portuguese and Sudanese. The Sudanese had no gas adjustment, but the later Portuguese had an adjustable gas regulation system ... which I really didn't need. But then, I was cleaning my AR10 regularly and shooting mostly 7.62 NATO ammo.
I HAVE FOUND THESE ORIGINAL AI BUILT AR10 RIFLES, BOTH SUDANESE AND PORTUGUESE, TO BE VERY FORGIVING FOR AMMO VARIATIONS, and more accurate and as reliable and durable as most other battle rifles. When I say forgiving, I mean that I have shot these original AR10 rifles with ammunition varying from the original .223/SABOT .308 Winchester factory Remington ACCELLERATOR loads, all the way up to 200 GR Winchester Silvertip hunting ammo. And all of these were reliable for feeding and function.
The problems with all the modern so called BIG CHASSIS ARs is that a decision was made to use the AR15 smaller diameter buffer tube, buffer, and spring. We can not know all the reasons why Stoner and Knight made this decision, but by doing so, they were hard up against the laws of physics. The Bolt/Carrier/Buffer/Spring equation has to follow the laws of physics regarding action/reaction. Given that the energy levels of the 7.62 NATO cartridge stay fairly constant, choosing to make the buffer tube smaller, required making the bolt carrier LONGER, with a reduced diameter tail, to approximate the same mass/inertia. And that is where all the fun really started.
I make the distinction between the old/classic/original AR10 rifles, with their larger parts, specifically bolt carrier outside diameter and buffer tube inside diameter, and all the modern AR15/AR10 HYBRIDS, which use the smaller diameter buffer tube, and usually as many AR15 parts as they can. And the Canadian government makes the same distinction. By Canadian legal definition, aka named specifically on the ORDER IN COUNCIL, AR15 rifles and any variant thereof are now restricted firearms. And the Canadian govt classifies all modern "Big Chassis" AR rifles as AR15 VARIANTS.
However, there is still some legal confusion regarding the ORIGINAL military issue AR10 rifles, which were almost all originally made as FULL AUTO. These were converted on import into canada, with the full auto parts removed, the hammer hook ground off, and they were allowed in as just any other rifle. BUT THEN, the laws changed, and any formerly full auto rifle was re-classified as "CONVERTED AUTO". BUT, recent precedents have declared that a SEMI AUTO ONLY ORIGINAL AR10 IS NOT A VARIANT OF THE AR 15 ... because quite simply, the AR10 came first, and the AR15 is a variant of the AR10.
COMPLICATED??
Maybe we should just go back to calling them BIG CHASSIS ARs,
LAZ 1
