The models are all very similar in look. From what I know all of the uppers(slides) are the same. But if you buy it for the option of buying the larger calibre centerfire upper, you will be limited. The P220 can only get the 45acp(its normal calibre) and the 226 and 229 can get either 9mm or 40. They use the normal factory lowers and are identical to the centerfire modles in that reguard. The uppers are very well crafted and fit, finish and machining are top notch. If you buy the centerfire upper, you get to practice and spend less using the 22lr upper. Nice advantage in using the same frame and trigger and controls while saving money(ton of money).
Those are the goods.
10 rounds at 15 yards. All in the 3 inch Shoot n See sticker(others behind on paper were from sighting in. This was my second magazine through the pistol(rounds 11-20)
The bad is the magazines for these are cheap plastic. But they cost as much as Sigs normal magazines(aprox $45). The magazines litterly probably cost about $1 or less to make. Why they cost what they do is beyond me. And they have poor fit. In the P220 model I have and from what I have read on many forums is they are too small from front to back. And due to this the magazine catch does not engage enough and the magazine tends to fall out when shooting. If you grab the base of the magazine when inserted in the pistol, you can move the base to the rear of the pistol and it will slide rite out without using the magazine release. There seems to be many with this issue. On the 226 and 229 models, I have seen where the magazine catch chews up the plastic in the area where the magazine catch engages the magazine. People have semi solved this by pressing the magazine release when inserting the magazine. To resolve the 220 dropping out issue, some have added material to the rear of the magazine to add length. This pushes the magazine towards the front of the grip and makes better engagement with the magazine release. Here is a pic of what I did to my forst mag. This was trial run and it has worked flawless so I havent tried to pretty it up as I will do with future magazines if Sig doesnt redo them.
What I did was cut a strip of plastic from a normal package(the clear stuff most hanging things come in at stores). I then used Gorilla Glue to secure it making sure I got enough around the edges so it wouldn't peal. Before this, the magazine would pop out after every shot. The gun would not feed due to this. Very frustrating. But after the mod I did to the magazine, I have fired aprox 600 rounds without a hitch. I shoot mostly CCI mini mags as they seem to be the recomended fodder for these semi auto pistols. They are a higher velocity round and have enough kick to cycle the slide reliably. I have had ok luck with the Winchester XpertHV(cheap at WalMart 500rnds for $13). But they do not have enough kick to cycle the gun reliably. I have tried some other high velocity stuff as well(CCI Stingers, Velocitors Aguilia Supermaximum) and all have worked flawless. The Sig's just need some punchy ammo. But most of those models of ammo are still very inexspensive. I usualy get the CCI Minimags at WalMart for about $6 per 100.
I just wish Sig would do something about the magazines. I have written them an email with my concerns but have not heard back from them yet. The guns are exceptional quality as all Sigs. But right now with them being reletively new, there is some issues mostly relating to magazines and their fitment.
I cant speak too much to the 226 and 229 models as to exact differences as I have never owned one. But I did handle all three when purchasing and decided on the P220 as it had a thinner grip. I think it uses a single stack magazine(centerfire form) and the 226 and 229 both are double stack and therefore a little thicker in the grip. I do not have huge hands(wear a medium to large glove) and the 220 had a better fit for me.
I am glad I bought the gun, but it is pricey for a 22LR. But you get the huge advantage of being able to just get the conversion upper(you get a discount coupon in the pistol kit good for one year). Being able to train with the same firearm is a huge advantage to me. Your memory of controls, etc will be the same when you use either calibre. It takes litterly seconds to swap calibres. If this is important to you, then this pistol makes an excellent choice. But if you just want a reliable 22 semi to shoot with, there are probably better choices in like a Ruger MKII or MKIII, or Buckmark, etc for less money.
If you buy the 22 version of the Sig and then buy the upper, it will cost you aprox $900 as compared to just buying the centerfire basic models which run aprox $850. So it is much more ecconomical to do it this way then buy the centerfore for $850 or so and then add the conversion for $350 to $400.