I have shot neither - but holding both - I liked the XCR better than the Sig 556 - at least when shouldering it in the gun shop.MrNuke7571 said:I had an XCR on order when they came out for a LONG time, then after getting charged 2x and lied to my face for 8 weeks after it 'shipped' per RobArms, I canceled it and told them to shove it.
Afterwards I held one and shot one at the range and I don't really like the weight of it. It is a chunk of milled metal basically. Way heavier than my AR's. Not saying they are not good or reliable, but I passed on them.
On the other hand, I shot a Sig 556 and I was impressed. With some new aesthetics like a handguard, it would make a sweet piston operated rifle. Highly accurate , little recoil and not too expensive. I might get one in the future when I get tired of my other rifles.