Your mags are rather stiff right out of the box, which is typical of the G3C.40 S&W. The springs can retain tension for a considerable amount of time even after being loaded.
I'd try two simple fixes before returning them to Taurus:
- Using a high-quality loader such as the Uplula, cycle load/unload a few times (it can really make that last round go in).
- To aid the springs in taking a set, leave them completely loaded for a week or two.
It could be worthwhile to get in touch with Taurus for a replacement spring or mag body if it still doesn't work.
Has anyone ever cut or altered the baseplate tab on? 40 G3C magazines to achieve full capacity, like some have done with G2C.