AR-10 vs AR-15 buffer tube threading spec?

[Cky]

Just recently I acquired smoke composites buttstock to be paired with Wilson combat AR10 lower. After threading the buttstock into the lower I’m seeing that the threads have minimal engagement between the two surfaces and there is substantial play. I was told by both manufacturers that the combination would be compatible.  

[Armed Eye Doc]

Do you have another buffer tube that you could test in the lower?  And, do you have another lower you could test the buffer tube with?  Those threads are universal between large and small frame receivers.  Any of those parts made to spec should work regardless of platform.

[Cky]

Right now I have wilsoncombat  factory ar10 buffer tube, smoke composite Millspec carbon buttstock and two WC ar10 lowers. Just out of desperation I did uninstall bustock tube from my factory built AR10 so I could see how their factory tube fits inside their setup and to my surprise the thread engagement isn’t great. I’ll try to record a video today to show the play between tube and lower. 

[Armed Eye Doc]

Did you try the smoke composite tube on the other lower?  If it fits without slop in the threads, then contact Wilson Combat about your lower.

[Cky]

No I haven’t. I still don’t know to who is out of spec, but my buddy works at a machine shop and is going to lend a hand with measurements.

 Here’s a quick video of the play between threads with the smoke composite buttstock. 

[Armed Eye Doc]

I would try the new tube in the good lower first.  From what you have said so far, I suspect the new lower is the out of spec part.  You might not need to measure.  It could be tolerance stacking between parts and measurements would confirm that.

[shooterrex]

Your video doesn't play. Pics or links to what you have would be a help.

If the AR10 buffer tube doesn't fit the lowers then it sounds like the wc lowers are the problem.

Wilson Combat make good parts but sometimes out of spec parts do get into the supply chain.

[98Z5V]

Where's the endplate and the castle nut?

[98Z5V]

For what it's worth, for Mods and Admins - this needs moved to a build thread.  This isn't the section for it.

Edited October 5, 2022 by 98Z5V

[blue109]

4 hours ago, Armed Eye Doc said:

I would try the new tube in the good lower first.  From what you have said so far, I suspect the new lower is the out of spec part.  You might not need to measure.  It could be tolerance stacking between parts and measurements would confirm that.

This. You don't need a machine shop. If multiple tubes fit correctly in one lower, and multiple tubes do not fit correctly in other lower....welp, problem solved with 5 min of work. 

Edited October 5, 2022 by blue109

[Cky]

The SC tube was tested on another AR10 lower form WC and it was the same result. Still loose and thread gap was excessive. 
 

Castle nut was used along with its respective counterpart, even tho it eliminated the slop I wouldn’t trust those threads with so little contact between them.

 

 

[98Z5V]

9 hours ago, Cky said:

The SC tube was tested on another AR10 lower form WC and it was the same result. Still loose and thread gap was excessive. 

That directly tells you where the issue is. 

[Cky]

Would you guys say it’s safe to use ? 
From what I could measure the thread overlap is about 2mm 

 

 

[shooterrex]

Why do you want to use a plastic buffer tube in place of a metal one?

The odds of 2 Wilson Combat lowers being out of spec are pretty slim.

 

[msgriff]

M16 TDP receiver extension thread specs (after finish):

1 3/16"-16 UN-2A 

Major Dia.   1.1860"/1.1766"

Pitch Dia.    1.1454"/1.1403"

Minor Dia.   1.1093" max