A friend is considering one of the above mentioned SIGs. Told him the prices are Very Nice, but he'd better move on it before it disappears. Bringing a couple of mine to the range Sunday for him to play with so he can decide. He asked me about SIG stocks. I mentioned I had a collapsing one I'd never tried out so...loosen 1 bolt, remove folding stock, slide collapsing stock in place, tighten bolt, and Done! Easier than I thought.
In the FWIW category: SIG is sending a 5.56 "taper cap" for free so I can put my non-SIG suppressor on my 5.56 MCX; due to arrive tomorrow. After going via their Director of Marketing, SIG has put me on their list to send me for free an adaptor to use the MCX upper on an AR lower and allow the use of SIG stocks with no buffer tube needed (ETA unknown). Why would I want to do that?...because Parker Mountain Machine is sending a MCX full auto kit consisting of an auto trip lever and pins. The trip lever connects the MCX upper to the M16 auto sear. SIG MCX uppers are already machined for the trip lever (look inside the upper towards the rear...you will see the slot and holes for the 2 pins to hold it in place), but SIG won't sell the trip lever to "civilians". MCX upper + trip lever + AR lower adaptor + M16 lower = full auto SIG fun. Doing it just because I can.