Coolest rifle I ever owned was a Sig StGw 57
Unfortunately I owned mine back in the early '90's when there was little to no 7.5 Swiss ammo, so I couldn't afford to feed it on my meager salary. I did learn that you can substitute a .284 Winchester case, size it, trim it, and it will work. Problem is, the 57 was absolutely abusive to brass and my cases only lasted 2-3 loadings before they split.
Look at the photo. See the white rectangle in the middle of the receiver? That's the "semi-auto" provision. In Switzerland they require the rifles be restricted (or they did) to semi-auto at rifle matches. So that white thing is a little spring steel tab that when sandwiched between the upper receiver and the trigger housing, will prevent the secondary disconnector/sear from deploying, making the rifle semi-auto.
US imported rifles included this tab, but they were obviously missing the FA parts. Other differences, the bolt carrier didn't have the hump for the FA disconnector, and the receiver was made in a way that it wouldn't accept a full auto trigger group without permanent modification to the receiver.
The sights were absolutely beautiful, save for the front. Both were folding to accommodate a scope. The rear stayed put, but the front could be bumped out of place without too much trouble; that was about the only real flaw of the rifle.
The integral bipod was slick, it could slide up or down the barrel jacket to be out near the front sight or near the receiver (not sure why someone would want a bipod that long near the reciever. Unfortunately the bipod didn't lock in the out position, so you had to take care not to bear down on it too much.
There were so many other little goodies on that rifle; I could go on and on.
Slick rifle, wish I had another one; but they go for like 6-8 grand these days.
ETA
Okay one more little snippet. Only the Swiss would design a rifle with controlled round ejection. And the extractor was the ejector also...again, really slick.