SIG MCX upper receiver with AR lower Receiver

Hello to all,

can i use the SIG MCX upper Receiver with an AR-15 lower Receiver?

I do not like the collapsible stock from the MCX. I would like to use a different stock but than i need the AR-15 buffer tube.

I would use the SIG MCX from the E&S 26017 Figure and the AR-15 lower from E&S.

E&S SIG MCX - upper Receiver

E&S AR-15 - lower Receiver

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You can, the only thing that will be off is the stock, the sig conversion to use the mcx upper on the at lower has a special buffer cap that folds but a standard ar buffer tube slides into but other than that yes, the mcx upper can go on an ar15 lower, Devgru specifically requested that as a feature from sig, here is the buffer adapter, the sig upper needs the adapter because the mcx doesn’t have a buffer tube for the recoil spring like the ar does so basically the tube has to be capped off because the mcx spring is internal in the receiver do the rifle wouldn’t cycle without the buffer plate, it’s a small detail you may choose to over look or you could try a bit of gunsmithing
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OK, thanks. I have seen this conversion kit but i thought it was just for use the SiG shoulder stock with an AR-15 lower. I have found this adapter you mentioned. Looks cool with that one and for the use of a different stock.


Here is a video with both adapters at 1:08:

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The SIG adapter was part on the Rattler kits to be paired with existing lowers in inventory.