I love the Sig Rifle. The only issue I have with it is that it's muzzle heavy with the US forearms. The folding stock on mine (the 2008 model) locks in place when extended. When you fold it, it doesn't have provisions to lock. It won't swing out but, it doesnt lock folded. Isn't an issue now but as the pivot wears.... My fixed stock is accurate and will eat Wolf ammo all day. I'm looking forward to the rear sight coming in to see if the folding stock one will perform as well as the fixed stock. Now if only my Sig Commando would come in...
The 556 is a great gun. It could have been the greatest though if the CEO didn't veto the original plans to just make a 16" barrelled 552 and call it the 556. Word is that he had issues with the folding stock model as well, at least according to the Sig reps I talked to.
The 556 is piston operated, and is basically a very accurate 5.56 AK. You don't get the high temps on the gas tubes when firing at high rates like in ARs, and the gun itself comes out of the box more accurate than the best DPMS.
The only reason I still have my AR is because I have tricked it out with close to 2 grand in mods, plus it can fire 458 socom with me just switching out the upper assembly. My 458 is a great Grizzley gun back in MT, because it hold 10 rounds of what I can describe as 45-70 +P rounds in a mil-spec 5.56 30 rd magazine. No change in followers or springs.
If Sig ever came out with a 458 upper, my AR would be gone faster than crack in Marion Berry's house. Great gun that 556 is.
I don't know if you've heard about Bruce Gray and his company GrayGuns (GGI) or not, but he's a wizard with SIG, HK, 1911 and other pistols. His associate, Scott, mentioned that they were planning on doing 556 custom work.
You might shoot them an email and see if they'd consider a .458 SOCOM conversion.
Funny thing about this rifle. I bought it about 6 months ago and put the eotech and sling on it. Never shot it. It sat in the safe forever. I've got the hots for the sig556. Bought 4 different models of them, with a sig556 pistol on order. Put the fs2000 for sale here. A buddie of mine from the bike club buys it and takes it home. His wife threatens to leave him so, I give him his money back and now have it back. So, I'm beginning to think it's fate for me to keep it , shoot it and enjoy...