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Discussion Starter · #1 · (Edited)
Sorry if this is a dumb question or has been asked before.

Has anyone tried using a 556R 7.62X39 lower on a 556 upper and used AK74 magazines to feed 5.56?

Just wondering if any of that would work together.
 

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Negative it will not work. Different bolt carriers and magazine wells. Look up sig 556xi supposedly designed to do multi caliber but never become reality
 

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Negative it will not work. Different bolt carriers and magazine wells. Look up sig 556xi supposedly designed to do multi caliber but never become reality
Have you tried it? I haven't. But I HAVE used a 556 lower with a 556R upper using x39 AR mags and fed the rifle fine. I did not have 74 mags to reverse the process the other way.
 

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Sig556ER; 551 HG; UBR stock w/MDT FSA; MFI rail/rear diopter; 550 FS; Versa-Pod bayo lug mount
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AK74 mags are made for 5.56×39 aren't they? I don't think 556Nato/223 will work in em. I like ur thinking though!
 

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Discussion Starter · #6 ·
Does anyone know if a plastic swiss 550 magazine will fit into a Sig 556R lower? Maybe someone can fit check a Swiss mag into an AK47?
 

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I have a 553R and a 556XI 7.62x39; not as interchangeable with 556's as you'd hope. Galil mags won't fit without modification though I haven't tried 5.45 mags yet.
 

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Discussion Starter · #8 ·
OK, what I have found so far. Circle K brand 5.45 and Sig 550 5.56 mags are both too wide to fit in the 556R mag well. The Galil magazine specs are all over the place. The one Galil magazine that I tried snapped right in, then would not come back out. I had to use a small flat head screwdriver to wiggle the mag release to get the Galil mag out. It looks like the rear Galil catch on the magazine is just a touch too long. Once the mag was in, it appeared that it would work. I did not try to feed any snap caps to test function. I will explore this more when I have some time.
 
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