Mill-spec and commercial buffer tube question


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crazyivan
January 27, 2012, 11:56 PM
Okay so here is my questions.

Do they both work on the same lower and if so
when switching over do you have to change anything other than the buffer tube?

tried the search but could find nothing.

Thanks in advance for your help!

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digdeep74
January 28, 2012, 12:34 AM
Buffer tubes will thread on any lower and not specific to anything other than the stock body.
For instance if you have a flat back mil-spec 4 position buffer tube on your rifle you cannot put a commercial magpul ctr stock body on it .
You would have to buy the mil-spec version or it wouldn't fit on or it would rattle because of the small but nevertheless size difference.

Z-Michigan
January 28, 2012, 12:35 AM
Either one works on any standard lower.

Your stock will have to change as very few stocks will fit both sizes of tube (Wilson is the only one I know of that does).

Your castle nut, end plate, buffer and buffer spring can all be used with either tube.

fatcat4620
January 28, 2012, 12:48 AM
You just need to make sure that your stock and tube match. Unless your going to war either one will work fine but a REAL mispec tube will be much stronger. So you know the term MILSPEC is tossed around a lot in the AR world and is often used to sell sub standard parts.

Onmilo
January 28, 2012, 02:17 AM
ANY commercial diameter collapser stock will fit either the commercial or mil-spec diameter tubes but because they are of the larger diameter, they will rattle around to a greater or lesser degree on the mil-spec diameter tubes.

Because of the lesser diameter, mil-spec stocks will not fit on commercial tubes.

End plates and castle nuts will work on either tube. HTH

madcratebuilder
January 28, 2012, 07:18 AM
Aside from the difference in diameter most commercial RE's are extruded 6000 series aluminum. A true mil-spec RE is forged 7075 aluminum.

gunnutery
January 28, 2012, 10:02 AM
So why in the world did anyone make the "commercial" specs in the first place? Isn't it just complicating another part that doesn't need to be?

Z-Michigan
January 28, 2012, 11:34 AM
Commercial tubes are cheaper to make, a combination of the material, process, and easier forming of threads (just cutting in vs. having to roll form, due to the greater diameter of the commercial tube).

crazyivan
January 28, 2012, 12:26 PM
Thanks for the help guys!

That is good to know that I just need to change the tube.

helotaxi
January 28, 2012, 01:48 PM
Someone could do an FEA of the different tube types to determine the actual difference in strength but it isn't like the commercial version is a failure waiting to happen. It would be more accurate to describe the mil-spec as well beyond what is needed and the commercial version as completely adequate. The primary substantive reason to go with a mil-spec receiver extension is that certain stocks are not available in a commercial version.

-v-
January 28, 2012, 01:51 PM
Your gun will explode and send the BCG through your shoulder, don't do it! :p

Seriously, all will be fine. Just make sure the stock diameter matches the tube diameter.

Z-Michigan
January 28, 2012, 10:00 PM
but it isn't like the commercial version is a failure waiting to happen. It would be more accurate to describe the mil-spec as well beyond what is needed and the commercial version as completely adequate.

The main thing is that the commercial design has threads that are shorter and don't mate as well into the receiver, so it is more likely to get pulled out or bent in the thread area. The commercial tube is also more likely to get bent while mortaring, or if you dash for cover like the US Army used to teach (maybe still does) using the rifle butt as a sort of stick to control your fall into a cover or prone position. Obviously these aren't important for most civilian users, but there is more reason than just being over-engineered.

madcratebuilder
January 29, 2012, 09:35 AM
Someone could do an FEA of the different tube types to determine the actual difference in strength but it isn't like the commercial version is a failure waiting to happen. It would be more accurate to describe the mil-spec as well beyond what is needed and the commercial version as completely adequate. The primary substantive reason to go with a mil-spec receiver extension is that certain stocks are not available in a commercial version.
100% agreement.

For civilian shooters I don't think it makes any difference. In ten plus years I have read about one or two commercial stock bending/breaking when pogoing a jammed round. You shouldn't get the rifle that jammed up to begin with.

I think it's important you know what the difference is between commercial/mil-spec/mil-spec diameter RE's so you can make a informed decision.

Onmilo
January 29, 2012, 09:51 AM
I can tell you from first hand experience that a certain commercial extension tube that comes from a manufacturer that starts with a 'B' did fail when the rifle was dropped off of a shooting bench and fell stock first onto a concrete pad.
Distance was 48" of drop, rifle impacted on left side edge of collapser stock and the force broke the stock latch and bent the extension tube at the junction of the castle nut severe enough to render the rifle unable to function.

Wasn't even a "combat malfunction", the rifle fell off a bench, something that happens pretty frequently, probably much more frequently than combat damage occurs to civilian owned AR15 rifles.

I now use VLTOR mil-spec+
extension tubes, (the genuine ones, not the made by someone else in Illinois versions.)

helotaxi
January 29, 2012, 10:19 AM
That sounds much more like a defective receiver extension than a failure due to the different manufacturing method and material.

I also only use mil-spec tubes but that's more because the first rifle I bought had one and I want it consistent across all my weapons.

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