I bought a 522 on a whim because I was looking for a .22lr with a 1/2-28 threads on the muzzle  and I found it for a great deal.  I really love this rifle. Out of the box with a tacpoint and bulk ammo I can cloverleaf at 25 yards.  I'd imagine if I had a proper optic on it with match ammo I'd get even tighter groups.  

So how similar is the 522 to the 556 aside from increased recoil?

Another thing I noticed was how well the 522 did with a suppressor. Being recoil operated its not surprising. Since the 556 is gas operated does it have the same or similar issues with a suppressor as an AR?

Can't respond directly to the SIG question, but I do have a Smith .22 as a companion to a Government Carbine; same sights (XS), A1 pistol grip,  and Magpul stock.
It does make a great trainer; can be fired indoors, and one is very reminiscent of the other in ergonomics and target acquistion.  But you are up against the same problem Colt tried to solve with thier floating chamber .45/.22 trainer; even tho' a 5.56 doesn't kick much, it does kick, and the moment after the sear breaks is just a different deal.  Followup shots are especially easy with the RF.
It's just the bargain you have to accept with the advantage of cheap shooting.
Moon

Here's my GSeriesFal pic.


They're so close its not funny. I just need to find a light rail so I can stick a pistol tac light on them and I'll be good to go.

I have both a Sig556 ER and the .522 classic and the main difference is weight.  The 522 is a ton of fun to shoot so buy extra mags and decent ammo.  They don't cycle the cheap stuff real well so I use CCI mini mags and they run flawlessly.  I run a Browning Buckmark Hollosite and it works great.  Have fun,
Backpacker

My 522 cycles everything from the cheapest federal lead nose to the cci mini mags. Doesnt seem to prefer one over the other.

OK. I get the perverbial foot in the pic thing. But lubricant, bucket, cup? Dont get it.

Also, get that thing on your toe looked at... I swear it winked at me.

It's not often I say this to a dude but...Nice Cans!

My 522 is the same way.




A while back there was a thread in GD about aimpoints. GseriesFal posted this pic of his tacpoint.



Since then any pic of a tacpoint has had a bucket, dirty keyboard, nearly empty cup, lube and some sort of foot herp.



Its sharpie.