I can only answer as follows:
I have one and for the most part like it. However I do wish I didn't have to sell my DI Bushmaster as it ran like greased lightning. The Ruger has yet to prove itself to me.
Fit and finish are good. It is a solid carbine. It uses a standard upper and lower with a custom cut rail from Troy. Interesting it's all pinned up but I'm not too concerned with any disassembly issues as the op rod is supposed to be self cleaning.
I would think is silly to not chrome line the chamber but the bore. On an AR rifle, the chamber is part of the barrel so I would assume it is chrome lined. Ruger does have a general inquiry option on their website.
Flash hider is not pinned and uses standard threads, I already changed mine out for a Phantom.
The trigger on mine is good enough that I am really on the fence as to whether I want to swap it out for something else. It is not match grade buy much nicer than any factory AR trigger I've shot yet. It's good enough that with a little more break in may just be fine as is.
Chamber spec.. hmm, dunno but again I would assume standard as it is listed as 5.56/.223. SAAMI (I again assume) would be .223 only. However, I did have a nasty failure to extract issue that (at this time) am blaming myself on. I think my chamber was too dirty and sticky from using the wrong grease and or possibly an ammo problem which I will look into once I dig my micrometers out. However, some research dug up this..
http://www.defensereview.com/ruger-sr-5 ... -solution/
I must say I am not calling this a fault with my carbine yet. I think it was just too sticky in the chamber for the problem I had. I will report on this board any and all issues I encounter with my Ruger SR556 and if no one has any complaints I may start a thread as a clearing house of sorts on any Ruger SR556 problems as there are some (which again needs to be pointed out that any new design has growing pains) issues.
There seems to be at least two different carriers used as well as bolts.
Also, it seems like every one has a slight offset with the transition from the uppers rail to the Troy rail. I cannot mount anything across that seam and every one that I have held has shown the same problem. This is a *very* minor issue and I am only noting for reference.
There is also two issues that follows all piston operated AR rifles and that is carrier tilt and cam pin drag. There is one documented issue with severe carrier tilt on an SR556 out there that I know of:
http://www.m4carbine.net/showthread.php ... 556&page=8
My carbine shows typical wear that has not progressed and I am not concerned. I will report anything that may come up.
It is *very* accurate. More accurate than the Bushmaster XM15 it replaced. I am very happy with the accuracy and once I get the fear I have with the failure to extract problems I will call mine a success. I do very much like the rifle so please don't view this as a negative post, just pointing out what I've learned.