Does anyone have a list or recommendations of stocks that when utilizing the folding knuckle/hinge that Sig sells will fold flat against the side of the rifle? I was using the Magpul SL-M for a little bit, but I found it didn’t fold flat against the gun, unlike the folding/collapsible stock does, for example. Would something like the CTR or maybe the newly released Magpul DT Carbine stock fold flat? Or are those still too wide?

I believe the CTR will get you as close as possible. Not sure about the rest.

I can personally attest to CTR stock will fold flat.

With the new folders for the Spear-LT a B5 Sopmod will fold and lock too.

The B5 Bravo will not, at least not when collapsed.