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3/26/2015 8:33:15 AM EDT
I am starting a 308 build and I was planing on buying a complete lower with factory stock. Now are the collapsable interchangeable between AR15 and .308? Or are the buffer tubes different size?
3/26/2015 9:45:10 AM EDT
[#1]
Buffer tubes (rifle and carbine length) are generally interchangeable, however, springs and buffers must be selected carefully for compatibility.  

See the .308 FAQ.  After you're there, if you scroll down the page a little, you will find another link for stock options.

3/26/2015 11:22:22 AM EDT
[#2]
I am using a Magpul UBR  adjustable stock for my LR308 build. It comes with their proprietary buffer tube. I bought the CAR 10 XH buffer and spring set from Clint at Heabyb Buffers.
3/26/2015 12:29:02 PM EDT
[#3]
Be aware that some here have had issues with bolt carrier rail location and lower receiver extension thread conflict, even when they sourced the "right" parts for a .308 carbine build.

The problem is that nobody is working off of an industry-wide technical data package, so it's a trial and error project in many cases.

That's not even talking about:

* Magazines
* Gas systems
* Bolts and extensions
* Upper receiver thread patterns for the barrel nut
* Lower Parts, especially TD and Pivot Pins, mag catch shafts, bolt catches and pins, Fire control space and pin locations
* Upper receiver rail height
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