Good Article on Big Chassis AR's

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9 years 11 months ago - 9 years 11 months ago #44127 by jtallen83
Good Article on Big Chassis AR's was created by jtallen83
I ran across a good article that runs down some issues that our favorite rifles occasionally have, starts on page 20;


fmgpublications.ipaperus.com/FMGPublications/GUNS/GUNS0315/
Last edit: 9 years 11 months ago by jtallen83.
The following user(s) said Thank You: Lazerus2011, Akai, Libertarian623

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9 years 11 months ago #44128 by Libertarian623
Replied by Libertarian623 on topic Good Article on Big Chassis AR's
All in all there are a lot of AR10's being built that don't have these difficulties. The platform has come a long ways in the last 15 years. As long as 308 remains a NATO round the design will continue to gain ground.

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9 years 11 months ago #44129 by jtallen83
Replied by jtallen83 on topic Good Article on Big Chassis AR's
One part of the article that stood out to me was the adjustable gas tube. I've heard plenty on adjustable gas blocks but had never heard of an adjustable tube. They didn't give much info on it but it would seem like a fragile way to go........

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9 years 8 months ago - 9 years 8 months ago #44701 by GGaskill
Replied by GGaskill on topic Good Article on Big Chassis AR's
My guess is that was just a careless referral to an adjustable gas block.

In any event, here is the subsequent article: May 2015 GUNS Mag . Starts on page 12.
Last edit: 9 years 8 months ago by GGaskill.
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9 years 7 months ago #44883 by GGaskill
Replied by GGaskill on topic Good Article on Big Chassis AR's
I noted his comments about firing pin holes being excessive and I have had perforated primers with my bolt gun loads, so I pulled the bolt and did some measuring using gauge pins. I found the hole would take a .077" pin freely and a .078" one tightly without being able to go through. I measured the firing pin diameter at .077". Just for comparison, I also measured the pin on my M1A; it was .074" which is not very different. Perhaps the lower pressure loads recommended for M14's is preventing perforations in the M1A as I have never had one there.

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9 years 7 months ago #44893 by OleCowboy
Replied by OleCowboy on topic Good Article on Big Chassis AR's
I enjoyed the first article, well have to hold a bit on the second, hopefully get to it tomorrow...

My take away for those that know me and how I think is not surprising. The AR 10 platform suffers from what I call 'linear' thinking. Firing pin hole is a great example.

AR 15 specs call for .063 +/-, THEREFORE the AR 10 being a scaled up AR 15 this then dictates the AR 10 should have a bigger FP hole, simple as that huh! Thus you get linear thinking...if the AR 15 is '1,x' then the AR 10 should be '1.5,x'.

All the problems discussed in part 1 are the result of linear thinking which results in component issues when the product is fielded. I saw NOTHING that should not have been captured in proper design and testing.
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9 years 7 months ago #44896 by Lazerus2011
Replied by Lazerus2011 on topic Good Article on Big Chassis AR's
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

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9 years 7 months ago #44897 by Siscowet
Replied by Siscowet on topic Good Article on Big Chassis AR's
Good summary of what is a grey area in original AR10 and subsequnetly 308AR design. It would be interesting to know if Armalite's products differ in this from the DPMS type designs, as DPMS, Knights, Remington, Bushmaster, etc. had a much more difficult "teething time" before reaching some degree of reliability.

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