Please, ignore. I was posting half asleep and saw P229 instead of P226 that OP was asking about.
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The only thing, I can suggest, is while here in the States, that would have been during the initial high capacity Magazine Ban, 12 round Magazines, would have been "Restricted". While I have seen both "Restricted" Sauer & Sohn, and Mec Gar 9mm 15 round Magazines, I've only seen Mec Gar "Restricted" 12 round P226 .357/.40 Magazines. Not sure of 10 round magazine design, but as far as Sauer & Sohn 9mm Magazines, both P228, and P226, all used the earlier follower style, which I don't believe would have allowed 12 round capacity in .357/.40.Now that I'm more awake, the earliest milled slide P226 in .40 I see is a 1997 gun, based on the serial list on the Green site. At this time, SIG was still using the German made mags. So, I think it's possible that there are German made dovetail back P226 mags for the .40/.357 floating out there, although I've never seen one.
These are exactly what my department issued looked like. I still have mine too. Prior to 2004 I had purchased extras and still have those too. Some unused.This was the mag that came with my dept issued 226 40 in the fall of 2001. View attachment 459677 View attachment 459679 View attachment 459680 View attachment 459677 View attachment 459679 View attachment 459680 View attachment 459681
Yes, I have some Pre-Ban Mec Gar P226 15 round 9mm Magazines, where they too used the earlier style Followers...The German magazines (as far as I know) do all use the earlier style of follower. The 10-round non-LEO .40/.357 Mec-Gar magazines also use the earlier style of follower though. So I guess the follower and the plastic block work together to limit the capacity, instead of just one or the other. So Mec-Gar magazines use both follower types, while the German magazines use just the old version. I guess the takeaway here then is that a standard 12-round .40/.357 P226 magazine tube, when given an older style of follower, wouldn't take the whole 12 rounds. Since a German magazine only uses the older style of follower, it makes sense that a dovetail 12-round .357/.40 P226 magazine does not exist.