If my being here on this forum doesn't say it, I am a dyed in the wool SIG guy. I own several and mainly carry SIGs routinely in either 9mm or .45ACP.
I have had nothing but bad luck when it comes to extended mags for SIGs. And I've given up. Its okay, although mildly disappointing, but all the same I trust my life to SIG (mostly) and Walther and Springfield Armory. Even SIG has recognized this obstacle and they've sent me replacement mag after replacement mag and I just figured its not meant to be.
Question: Are there any other gun makers that have this problem with extended mags?
A buddy of mine who is a SWAT guy and part-time range officer opines that the reason the extended mags don't work well is because of the extension for the pinky finger and when squeezing there's a tendency to push down and that is causing the mag to drop. I don't know if I buy into that. Thoughts?
Pat, I'm once again, going to go out on the limb here... and one of these days it'll break.
It boils down to trying to stuff more into the same space... namely more rounds, and larger rounds into the same sized envelope. One of their primary ways is to use smaller diameter wire to make the springs, including different alloys. The delicate balance between the upward spring pressure on the cartridges feeding from the magazine, and the force of the recoil spring stripping the round from the feed lips, and into the barrels chamber, when unbalanced will cause feeding problems.
We all have experienced the difficulty in loading a new magazine to its listed capacity, until the magazine spring takes its initial "set", only to what seems a short time later, that the spring doesn't have enough tension to lock the slide to the rear, when the magazine is empty... requiring a replacement.
One of the problems is, a lot of these newer magazines use a different style follower, to allow for the insertion of more rounds, and the springs fit "into" a recess, "spring pocket" into the bottom of the follower, while the original followers, had projection that the spring fit "onto". (See attachment) These are out of a 15 round P226 magazine, and a 15 round P229-1 magazine, both 9mm. The "Older" P228 9mm magazines, which held 13 rounds, used the same follower, as the P226.
Finding replacement springs is one matter, finding replacement followers is another. Many are irritated that Sig does not carry replacements, but the bottom line is that magazines are considered "consumable" items, but at the price that Sig wants, for their magazines, consumers want to "repair" them at a cost savings. The manufacturers themselves, normally don't advertise the individual components, as they make more money, selling the entire magazine. You know that they have them, because they need to repair their products that are still under warranty, unless it is more cost effective for them to "write off" defective merchandise as losses, on their taxes.
Your buddies theory, about the mag extensions flexibility, causing problems, I have a hard time buying. The extension doesn't lock the magazines feed lips into position, the mag catch into the body of the magazine does. Again, I believe it's the use of smaller diameter spring wire, which ultimately lessens the springs useful life span. The minimal flexing of the extension would have a negligible effect on the springs pressure on the follower, IMHO.
As far as other makes, Colt M1911 magazines, 7 versus 8 round Government length, 6 round versus 7 Officers length, Browning High Power, 13 versus 15 round.