[sig78257]

Unless I read it wrong (and I might have), Top Gun now has an XGrip adapter for a sub compact to take full size mags. I had to get a sc module for my compact to get the small size since Sig seems to be putting a low priority on supplying parts for the 320 anymore (at least Grip Modules and magazines). I plan to carry the 320 with the 12 round mag and have the 21 mag as an extra if the adapter works out.

 

[Alloy07]

i picked up the 17 round full size mag x grip adapter to the SC grip, the 15 round compact adapter to the SC grip and the 17 round adapter for the Compact grip from Top Gun they work perfect and IMO feel great .
I picked up a second set from Greg Cote LLC .

 

[Dismas316]

I second alloy07. They fit much more snug than the originals.

 

[LGM]

I just email them with this question, let's see.