AR15 Uppers?

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[85_Ranger4x4]

The 6.8 SPC may very well replace the current military 5.56mm ammunition in the near future. It's getting more common and it is a new trend for AR15s that is gaining popularity very rapidly. I'll stick with 5.56 at this time for availability but will probably purchase a 6.8 SPC chambered upper in the near future and swap uppers onto my lower. It is election season so AR parts are currently scarce. A lot of stuff on backorder and buying a good upper where the lead time used to take 3 days can be as much as 2-3 months currently. This is typical of election season.

Do standard 5.56 lowers interchange? Stag shows a plain lower and a 6.8 lower...

http://www.stagarms.com/index.php?cPath=18_32

And then I am showing what looks like a loaded lower half for $300:

http://www.stagarms.com/product_info.php?cPath=18_32&products_id=237

And an upper half for $595:

http://www.stagarms.com/product_info.php?cPath=14_24&products_id=318

half + half should = whole right? Comes out at $895 vs $1055 for the whole thing with a fixed stock. I am still on the fence about stocks but they are the same price with a lower half.

Aside from probably a mag or two what am I short?

http://www.stagarms.com/product_info.php?cPath=13_22&products_id=314

 

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