I have a lot of dumb questions on this subject. This discussion seemed to help:
http://www.m4carbine.net/showthread.php?4611-Vltor-Vs-Magpul-Vs-Sopmod-collapsable-stocks

What I understand is that there are two buffer tube types, milspec and the lower quality commercial buffer tube. Milspec is forged and commercial is extruded? Are the outside diameters the same?

I assume y'all only use milspec?

What is the technical difference if any between a reciever extension vs a buffer tube? One is M16 and the other is M4? Are dimensions different? Is it just semantics?

(from Brownell's: "Mil-Spec fits smaller 1.14" O.D. buffer tubes on Colt-manufactured M4 and similar mil-spec carbines. Commercial fits larger diameter 1.17" O.D. commercial buffer tubes."

Thanks y'all... I have more questions as I go...

http://www.m4carbine.net/showthread.php?101-Buffer-Tube-Basics

As for stocks, I use SOPMOD stocks.

SOPMOD.... arrrggggg $$$$$$$$

They run about $200 or so???

Thanks for the link; very informative, especially about commercial tubes/threads failure.

on my 308 the sophmod did not fit well enough to keep from rattling, at least not the ones the dealer had in stock, I got a CTR magpul stock that locks and I like it OK. I prefer the sophmod however.

I have magpuls ACS both in regular and one in light configuration. I also have milspec and commercial. The main difference between the two is the diameter of the tube. The commerical has a bigger tube and the back of the tube has a slant to it where the milspec is smaller and has a flat back to it. Other than that you can find the majority of stocks in both configurations. As far as using one over the other there is no difference in using one over the other unless you want to be tacti-cool then you will need to have milspec.

SOPMOD or Magpul ACS. Those are my two favorite after trying a bunch.

I think the ones with a cheek swell work best.

B5 sold at Brownells and other places makes the current SOPMOD stocks for around $100 and they fit tight.

Jimmy, I've never seen a real SOPMOD that was loose.

Edit

my FNAR is setup with ACE folder,I really like the feel of the stock

+1

I've had 2 LMT's and 2 B5's. The LMT's were both a tighter fit.

There are some chinese copies for air soft out there.

LMT's have been a perfect fit for me, I've had probably 8-10 and sold a few more.
The first 3-4 B5 stocks I've had were so tight I could barely collapse them until they wore in and then they were/are a perfect fit. The last one I bought was after they loosened up the dimensions and it fit perfectly out of the box.

one thing most people leave out about mil spec and commercial is generally a commercial tube and stock extend out LONGER. for me this is a very good thing as most ar 15's feel like they are sized for an elf. that extra 1" or so really helps me. I not huge just 6-1. I like the RRA operator stocks they are a commercial tube and are very nice to shoot. with a commercial tube and its extra length you can always adjust in, my 11 yr shot mine yesterday with not issues

I like the Ace skeleton and socom stocks and the Magpul PRS. I have a couple cheaper Magpuls on some lowers but you get what you pay for. They work but rattle a bit.

Magpul fixed MOE stock. Takes full length spring and buffer. Fits better than the A2 stock and provides better cheek weld and off hand support when shooting prone. Not a fan of adjustable stocks.

YMMV

I've never been tacticool in regards to my AR's and have had great luck with the Mag pul CTR's for an adjustable stock. They have always fit my recoil tubes well and with the secondary friction lock (which automatically releases when you hit the adjustment release) they have almost no wiggle. Seems as stable as anything else outside of fixed stocks.

I like the Magpul CTR too. Locks up solid and not a heavy as some of the others.