Brand new member; looking for insight (thank you in advance!) I have a 1992 vintage SIG P220 in 45acp for which I recently ordered an Alien Gear holster for. The kydex shell that AG sent does not fit the gun; thinking possibly a defective shell was sent; AG sent me another. Exactly the same as first; does not fit the gun. Long and short; I believe SIG changed the P220 45ACP externally at some point; and AG only has molds for the "newer" configuration. We tried one for a P226, but it does not fit either. My inquiry here (and goal) is to define when the change was made & how to properly reference the "old" vs "new" configuration so Alien Gear and I can figure out what we need to do in order to get my holster squared away. Any guidance would be appreciated!

You most likely have a stamped slide with no rail. It is the smallest of the bunch.

Strange.

Generally, if there’s going to be a fit problem it’s trying to put a recent production P220 with the accessory rail into a holster designed for an early gun. My agency has old and new 220s and the older guns without the rail and with the carbon steel slides fit in any of the newer holsters.

The only thing I can think of is perhaps the trigger guard was made smaller with the addition of the rail. I know that occurred with the P229. Usually it’s the rail that causes the fit problem, but maybe that’s what’s going on with the holsters you’ve tried.

Don't know much about Sigs but I do own a 80s vintage 220 that I ordered a set of 220 grips and found that grips for later vintage 220 will not fit so my experience there are some differences from earlier and later models. At the same time I ordered the grips I ordered a holster from Milt Sparks not knowing there was any differences and the stock 220 holster I received fits my gun fine. As far as overall dimension since the holster was ordered in 2010 and the gun is from the 80s in my experience there was no significant change. In your case you may have some odd ball that does not fit the norm. There are a lot of Sig experts here and maybe they will answer your question.

I looked at a couple of P220s today, one serial number G3006xx with carbon steel slide and no rail, and one from a few years ago with stainless slide and accessory rail. Except for the rail, I could see no dimensional differences between the two frames. I was especially careful to look at the trigger guards, and they appear the same. There could, though, be enough actual difference to cause problems with a molded Kydex holster, I suppose.

The only other thing I can think of was that at one point the P220 frame was beefed up, so that might have resulted in a dimensional change, but I would think that older guns would fit holsters for the newer. A SIGforum post:

“That was the year [1994] the P220 frame was strengthened for better tolerance of +P 45ACP ammo with serial number 219166 and above pistols.”

Thank you all; a little more detail: Mine has no rail, for one thing. Serial is G205xxx. Alien Gear shells are very closely molded to the gun; so I'm able to see and pretty closely measure some of the differences. Most obvious difference I see is that the gun the shell is molded for has a bevel on the top corners of the slide that measures about 3/16" wide and about 30 deg off vertical. the grooves on the side of the slide stop at this bevel and do not go all the way to the top of the slide. On my gun, on the other hand, the grooves go all the way to the top of edge/corner of the slide where the gentle radius over the top of the slide starts. When I measure from the bottom of the trigger guard to the top edge of the bevel on the molded shell, I get about 2.750". When I measure the same on my gun, I get about 2.930. I can't see enough definition in the kydex to tell if my trigger guard is larger or same size though. I even found some pictures online of a P220/45ACP that had the bevel plainly showing along the top rear edges of the slide; but I can't figure out how to differentiate that from mine in terms of a model number or "generation" designation from SIG. Maybe there's a meaningful clue in here... thank you!