Interesting.
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I guess I can't edit my post but I was going off of memory and if I remember correctly after the Gen4's came out Glock changed the 26 Springs. The old springs were black and the new ones were heavier springs. I remember trying to find some of the old ones for my Gen 3's without much success. So the numbers I gave might not be correct.
Remembered I have an old one in my carry gun. One on the left is an FCS Serial # 26, my CCW since 2004 or so. One on the right is a M serial # 26. (I don't think the one on right is original but what they upgraded to with the Gen 4's).
With a 43X/48, I avoid +P ammo for improved reliability, but on my 19/17 I gravitate towards it on the theory more oomph might enhance reliability, especially with a compromised grip. With a heavier RSA, the 26 might also be a candidate for a +P load like 124 Gold Dot.
My local BL pusher had two in the case, so I grabbed the tighter one. (Blue label pricing is the devil.) I want to have it direct milled for an optic, I just need to decide which one.