I've been trying to find a 556R for sale and am not having good luck. But I've noticed 556 in 5.56x45 are far easier to locate.

https://sigforum.com/eve/forums...0601935/m/4080092574

So a crazy thought came to mind!
Why not re-barrel a '556' 5.56x45 as a 7.62x39, to create a hybrid-hybrid franken gun?

I would use ASC mags in a 'Classic' type lower with an M4 style stock, as is my 'SCM' model which has been excellent for me.

To that do any of you know to recall if the gasblock & regulator cap for the 556 was same gas port sizing as the 556R?

I've done some cursory Google queries and cannot find a definitive statement.

TY for assistance! :-)

- Janq

I'm still blown away by the fact that those rifles supposedly didn't sell well enough for SIG to keep making and supporting them, but still sell for what is (IMH cheap-assed O) silly amounts of money.

The barrel (and probably the feed way) would probably take some expensive work. 7.62x39 ports on other rifles (ARs and AKs alike, if I understand correctly) tend to be larger than those on 5.56s, and not just because everyone seems to prefer that 7.62x39s be slightly (to surprisingly to outrageously - friends don't let friends buy IO!) overgassed.

My WAG, FWIW, is that whoever does the work might be able to safely modify a 5.56 part for the 7.62x39. Maybe it makes sense to find a gunsmith to do the work and ask that gunsmith whether the modification can be done rather than trying to find the right factory part as a part of checking the feasibility of the project.

Beyond that, maybe check with JDI, Gatewood Supply, or Colorado Gun Sales - people who handle 551/552/553 parts - to see if they have something you can use or can point you in the right direction. Come to think of it, that may also wind up being a good way to source a barrel and they may be able to give you good guidance on port sizing. Normally I'd also suggest Numrich, but they're not exactly SIG specialists and a quick look there didn't turn up any parts you might use.

This message has been edited. Last edited by: Il Cattivo,

My advice is wait till you find a Sig 556R.
Be aware that changing the barrel isn't
so simple. The barrel threads are not timed like a swiss, meaning the new barrel probably will need gas ports welded and new holes drilled. Then the head spacing will need attention. And you need a gunsmith with a sig 556 reciever fixture to unscrew and screw in new barrel.
You'd be better off getting a factory 556R.

Adco firearms used to work on 556's.

https://adcofirearms.com/

This message has been edited. Last edited by: Greymann,

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quote:

Originally posted by Janq:
I've been trying to find a 556R for sale and am not having good luck. But I've noticed 556 in 5.56x45 are far easier to locate.

<snip>
- Janq

I'm guessing you haven't checked Gunbroker ... they have 2 listed as well as a Sig Sauer R556xi Factory SBR 10"
If you keep your not in a hurry you might find a SiG P556Xi 762 which is how I bought mine and then did a form 1 to SBR it

Henry....you might want to try the M+M M10X, which is a Sig55x derivative in 7,62x39 and is currently supported unlike the Sig 556 platform.