Like I mentioned in the PWS piston thread, I'm a big fan of "pistondriven" rifles.
That being said, when I went shopping for second semi-auto I went for a piston rifle. Living in Euroland and having always been a big fan of Swiss firearms I opted to get me a SG550.
Unfortunately has it been sort of a safequeen for quite some years, mainly because I got involved in the Lowlandsversion of 3-Gun and there's far more bling out there for an AR than there's for a SIG.
Anyway, a year ago I saw the light and started "improving" my SG550.
Attached is a pictorial of the SG550 in it's many guises over the past few years, all the way up to its most recent rendition.
It went from "plain jane" through "über-railed" back to something more "KISS".

Did I mention that it runs like Swiss clockwork