I can only relate from my persobal experiences with both the 556 and the XCR. I bought an XCR in 2006 and took it to a training trip in Nevada. We ran over 1k rounds of green tip through in less than an hour. I experienced a good number of light strikes and trigger hang ups. The great thing about the design setup with the XCR allowed me to immediately rack the charging handle without coming off target or losing my cheek weld. RA has reworked the trigger so I believe those hang ups are no longer an issue. You'll have to break her in a bit to get her to run without hiccups. The caliber conversions are also a pretty cool option with the XCR. I have no experience with the FS2000 other than hefting it at the shop, but I can say my buddy's Sig 556 runs flawlessly right out of the box. It's a bit muzzle heavy (who cares, aids in recoil mitigation) , the charging handle reciprocates and is on the right side, (similar to your WASR) and most importantly in a combat rifle, it is utterly reliable.