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Double Diamond SIG522 stock adaptor

Last month you may recall I looked at the SIG522 DMR from Lantac, which was the basic rifle fitted with a number of accessories, one of which was the Double Diamond (DD) butt conversion. The 522 features a side-folding/length-adjustable, synthetic stock, which is OK but I have always found it a bit wobbly. The DD kit replaces the original and makes use of AR parts and takes about 5 minutes to fit; even if you are technically disadvantaged… This example was supplied by North West Custom Parts and here’s how it all goes together.


The DD adaptor is a shaped, alloy block that fits into the rear of the rifle and replaces the issue stock. It has a locking lug that works with the existing catch and is threaded at the rear to accept AR15 buffer tubes. However, the tube, lock nut, anti-rotation plate along with the butt of your choice are all extra. To remove the original; drive out the hinge pin on the right of the lower receiver.  It comes with a small, Bellevue-type washer and two roll pins. All you do is position the block in the hinge points and, with the washer between the lower lug and base, drive the pin back in. On my rifle I put the washer on top by mistake and though the block folds and deploys the catch will not lock as it was out of line. So it needs to go on the bottom, or in some cases is not required at all. But it fits without any modifications. One roll pin can be driven into the hole in the block to secure the hinge pin in position; which is not always nessecary. The second is pushed in at the rear and blocks the locking catch from operating should you wish a permanently fixed butt; again not essential.

You choose

With the adaptor fitted, secure the buffer tube with the anti-rotation plate and nut and the choice of butt is yours. NWCP have a wide selection in this area all the way from a basic, CAR 15-type right up to the more exotic stuff, it all depends on what you fancy or can afford. The difference in stability is immediately noticeable as your head/sight position is much improved and the wider stock really does offer better support. If there is a down side it’s the fact that though the butt can fold to the side it cannot lock in this position. Frankly a small price to pay for something that makes the SIG far more shootable!

•Name: Double Diamond SIG522 stock adaptor - £95
•Buffer tube - £45
•Lock nut - £7.50
•Receiver plate - £7.50
•Butts starting from - £25 - £250 (depending on make/model)
•Contact: North West Custom Parts, 0161 408 1155
•For: A most practical replacement for the original SIG butt
•Against: You must factor in the price of the buffer tube etc., which will up the cost
•Verdict: A definite improvement over the original, but not that cheap given the extras you need


1, The Double Diamond stock adaptor now offers the opportunity to fit a CAR15, telescopic-type butt to your SIG522
2, Detail of the adaptor note the butt latch and the holes for the hinge and lock-out roll pins

All Prices Are Guides Due to the Changes in US & European Exchange Rates

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Double Diamond SIG522 stock adaptor
Double Diamond SIG522 stock adaptor
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