Glock 30sf Width: 1.27
http://us.glock.com/products/model/g30sf
Glock 30s Width 1.28
http://us.glock.com/products/model/g30s
Glock's website advertises the Glock 30s as having a slimmer slide than the Glock 30sf. So, I don't really believe anything now. I have a G29 slide right next to my Sig P220 slide (stamped slide). It's obvious the G29 is bigger. I'm going to get a caliper tomorrow and measure it. My money is on the Sig being slimmer.
Case not closed.
I think the manufacturers are measuring from the widest point only, rather than the various elements (slide, grip).
The Glock 30 comes off as much wider in the slide area, while the P220 is slightly more narrow. Overall, they're about the same. Pictured is a Glock 21, which has the same width as the 30. The Glock 30 slide
feels much wider than it is. However, the photos below show the differences as negligible at the rear of the slide. Notice the SIG tapers slightly towards the muzzle, though the slide release adds width in that location only. Glocks are called "Blocks" for a reason.
The practical differences are:
1) The wider slide of the Glock can be felt in IWB or appendix IWB holsters.
2) The grip of the Glock is slightly longer. The SIG 8 round magazines add quite a bit of height and make it nearly the same length.
3) SIG magazines are easier to hide.
G21 vs P220
Guns in holsters with nearly no difference (holsters made with .06" kydex)
Magazines