I've sent my SGL31-44 off to Mario at Piece of History to have it converted to a 5.5mm folder, but he may not send it back before the end of the year. I'm not in a huge hurry plus I want Russian selector markings engraved so I'm ok with the wait on this one.
My 31-61 was converted by Keith at Tac47industries and I'm happy with it, though to be honest he's not a collector grade AK builder and doesn't want to be. He specializes in S12 conversions and turns out some really nice stuff but he also knows his way around an AK and has done several side folder conversions for me and friends.
Just to be clear he's become a close friend of mine and we go shooting all the time, our friendship originally stemmed from the work he did on my S12 a few years ago. If you're looking for a Ted Marshal guy to handle every collector level detail of a clone he's not the one you're after, but if you want something done right that's functional like it's supposed to be then maybe give him a buzz.
And it's not actually AK100 series folding stocks, it's AK74M series folding stocks. The 100 series is based on the 74M and came after the 74M did
Both 5.5mm conversions:
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