I fitted a Kart 40SW barrel and Delta slide to the Colt Match10 over the weekend.

The Colt marked ($26) flat follower clips are not so good. Some unmarked ($12) 10mm round follower mags worked a bit better. These followers are the tubular no tilt type.

Got good groups with this:

40SW mixed cases,
180Montana Gold HP
Silhouette 7gr. (7.5 is max)

I have to measure/try a few recoil springs.

The original 10mm is a dual spring.

so you are saying your having problems with the mags. Not working properly.

The 10mm works ok. the 40 mags , the first round is a problem sometimes and they won't hold the slide back (follower jumps over it)