Puzzeled about AR-15 Stocks

[alfsauve]

Okay, so I should probably take this to the AR-15 board, but it's so hard to read.  Maybe someone here can clear this up.

There seems to be two sizes of AR-15 butt stocks.  "Commercial" and "Mil Spec".   One says it's 1.168" the other 1.148"

What the heck are they measuring?    Is it the thread dimension?  Is it the buffer tube.

[Pathfinder]

Alf, these are the diameters of the buffer tube. It makes a difference since the buffer tube screws directly into the lower receiver.

[alfsauve]

Alf, these are the diameters of the buffer tube. It makes a difference since the buffer tube screws directly into the lower receiver.

But exactly where do I take the measurement?
Is it the tube itself somewhere after the threads?  Or the outside diameter threaded part of the tube?  Or the inside thread diameter of the lower threaded part of the lower?  or something else.

When I took measurements on my A2 National Match (supposedly Mil-Spec) none of them match the 1.168 or 1.148.

Let me pose the question another way.  If I have a lower that's not marked what do I need to measure to determine whether to buy a "commercial" or a "mil-spec" stock?

[Big Frank]

I think the #s refer to the O.D. of the buffer tube. As far as I know it only applies to collapsible stocks. I don't have any way to measure mine.

[Timothy]

From Brownells..

Magpul Original Equipment (MOE) carbine buttstock provides the quality, durability, and ergonomic benefits of Magpul’s CTR stock in a rugged, economical, drop-in package. Strong, A-frame design is lightweight and comfortable, yet provides operator with plenty of support. Comb contour is wider than standard issue M4 stock to help shooter maintain a solid, consistent cheekweld. Streamlined exterior and protected release lever won’t snag on clothing, gear, vehicle interior, or vegetation. Heavy duty, spring-loaded release lever allows fast length-of-pull adjustments and won’t dig into your hand. Impact- and heat-resistant, polymer construction includes molded-in reinforcements at stress points, plus two slots for web slings and a hole for a toe-mounted sling swivel or clip-on sling. Soft, synthetic rubber buttpad increases comfort and helps prevent slippage. Mil-Spec fits 1.14" O.D. buffer tubes on Colt-manufactured M4 and similar mil-spec tubes that accept both four- and six-position collapsible stocks. Commercial fits larger, 1.17" O.D. commercial carbine buffer tubes. Buffer tube, carbine buffer, receiver extension nut, and carbine-length action spring not included. Available in Black and three popular tactical colors, Dark Earth, O.D. Green, and Foliage Green.

[Sponsor]

[Timothy]

And this..

[blackwolfe]

But exactly where do I take the measurement?
Is it the tube itself somewhere after the threads?  Or the outside diameter threaded part of the tube?  Or the inside thread diameter of the lower threaded part of the lower?  or something else.

When I took measurements on my A2 National Match (supposedly Mil-Spec) none of them match the 1.168 or 1.148.

Let me pose the question another way.  If I have a lower that's not marked what do I need to measure to determine whether to buy a "commercial" or a "mil-spec" stock?

I think the threads will work on either.  I thought I remember reading some place one time that even though the Milspec buffer tube was a smaller diameter  it is stronger and more costly to manufacture than the commercial version.

[Timothy]

I think the threads will work on either.  I thought I remember reading some place one time that even though the Milspec buffer tube was a smaller diameter  it is stronger and more costly to manufacture than the commercial version.

http://www.ar15pro.net/2008/09/milspec-buffer-tubes-vs-commercial.html

Different materials, 7075 forged vs 6061 extrusion.

[fightingquaker13]

Quaker, who has just gotten a headache from all the techno speak, would suggest the following. Write down the serial number and call whoever made the reciever. They should be able to tell you. This seems a lot easier than measuring fractions of an inch on a threaded tube.
FQ13

[Timothy]

Quaker, who has just gotten a headache. would suggest the following. Write down the serial number and call whoever made the reciever. They should be able to tell you. This seems a lot easier than measuring fractions of an inch on a threaded tube.
FQ13

Twenty thousands difference on an O.D. is pretty easy to measure, even with a tape measure with 1/32 graduation.

Measure the circumference and divide by pi...