Are these limited capacity 10-round magazines or standard capacity 13-round magazines?
I'm not sure if there's another type of follower you could use in .357 10-round magazines. I know with 9mm 10-round magazines you can use 9mm3 followers if you experience failures to feed with the original 10-round followers. Perhaps .40 #5 followers would work in .357 10-round magazines.
The first thing I'd try is different ammo, I've never shot .357SIG so I couldn't make any recommendations but Speer Gold Dot 125gr may be a good place to start.
There seemed to be a problem in some .357SIG models, particularly G32's and G33's where the feed ramp seemed to be the culprit. The only solution for a lot people was to use an aftermarket barrel that had the older feed ramp design, I think a lot of people used KKM barrels and that fixed it for them.
Glock's recent extractors seem to have more variation in their specs and be more likely to fit too tight causing failures to feed, if nothing else seems to work you might try a replacement .357/.40 LCI extractor.
G23 G27 .40 S&W Club Member# 4520
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Last edited by voyager4520; 10-08-2012 at 17:30..