I noticed that sig on the 556 series of rifles has 2 types of receivers. 1 that is a flat sided in the pic the rifle on the right and the other on the left has some raised areas both in front of the mag well. Why did they change the design and what was the later one. And is one better than the other.You can see in the pic what I'm talking about. I got the pic from the sig pic tread at the top of this forum.


Thanks

One's an original 556, the other is a later 'classic' 'swiss style' folder.


They eliminated the lightening cuts on the later 'swiss style/classic' lower receiver I suspect to save money. Does look dope though, don't it?


 

So the slab side receiver would be like a 2nd generation receiver.

you can think of it that way, but I wouldn't.

 

The "classic" lower also had a few iterations. You can see in that example that the mag release button has a machined "fence" around it but in even later iterations they eliminated that. Then, the XI lower receiver is (IIRC) backwards compatible with the previous SIG55x series, and it has full ambi controls. Then you add in the swiss rock-n-lock-mag lower and you have yet another version.


Furthermore, until the XI, the "original" lower was still available, with no buttstock, on the pistol:




This was sold concurrent with the "classic" folding stock model, so it's not really correct to think of them as "generations", although the M4-style lower did come earlier.


Basically you've just got the two types:


A: The earlier lower that can accept an M4-style buffer tube in the rear, used on the earliest 556's and pistols and

B: The "classic" lower that accepted a swiss-style folding stock, that was introduced with the "Classic" models.

(Also: C: the XI lower)