Commercial vs Mil Spec buffer tubes. Someone please clear up my question.

[twaits]

Okay, could someone here who really knows tell me if there is some kind of advantage to a Mil-Spec diameter buffer tube over a commercial spec?
So far the only thing I can gather from this is that the tube diameter on a mil-spec tube is slightly smaller than the threads. The commercial spec tube is slightly larger than the mil spec being the same diameter as the reciever threads. This cuts out the extra cost of having to mill the tube down to mil-spec size.
Why did the "mil-spec" dictate that the tube be smaller diameter than the threads?
A lot of people seem to demand "mil-spec" tubes and I would just like to know if there is a reason other than "well its mil-spec and thats what I want"

Thanks to anyone that can clear this up and also hopefully be able to list their sources of information to the reason.

[William B.]

this post is based on information received from individuals more knowledgable than I.

Threads on mil-spec receiver extensions are created using the rolled-thread process. This process does not cut any material out to create the threads (which would create stresses in the material). Instead, existing material is extruded to create them. This is the reason that mil-spec tubes are a slightly smaller diameter than their threads. From what I understand the rolled-thread process creates stronger threads than the cut-thread process (the process used to create threads on commercial tubes). My father was a machinist in the Marine Corps as well as the civilian world and he agrees with this assessment. I'm not sure, however, how negligible or significant the difference in strength is. I apologize for not having any sources handy at the moment. If you do some searching on everyspec.com, though, you may be able to find something more solid than this.

The following link compares rolled and cut threading on bolts and screws. Although they are not speaking specifically about receiver extensions, some of the information is still applicable. http://www.portlandbolt.com/faqs/rol...-threads-bolts

[Fortibus55]

That's something I've wondered about as well. Thanks for asking it Twaits. And thanks for the information William B.