Question to the group. I have the P320 Compact and would like to get a +5 Aluminum Baseplate extension or even an additional mag with extended baseplate, but in reading the descriptions for Hyve, Taran, etc. it doesn't appear that any of them fit the Compact frame.
Does anyone know of any manufacturers? TIA

I have several 21 round 320 mags that came with the Tacops. They fit and function in just about anything 250 or 320. Might be worth considering. I see them in stock at several online retailers.

I installed five Taran Tactical +5 baseplates on P320 magazines this morning. They're intended primarily for competition, although they could be run defensively, too. They're going to stick out a long way in a Compact. The TTI +5 baseplates can be put on a 15-round Compact magazine, but the springs for them (ordered extra) are for 17 round magazines: the TTI +5 baseplates are meant to go on the 17 round 9mm mags, or the 14 round .40 mags (full size mags). In each case, they're designed to fit and stay just within the 140mm competition length limit for "limited" magazines.

What you'll run into if attaching to a 15 round magazine is a spring that's a bit too long (if you use the taran tactical; and too short if you use the Sig factory spring). You'll also run into the tab that is the baseplate retention device; a small metal rod that protrudes upward from the baseplate, and that will run into the P320 compact frame.

If you install the TTI +5 baseplate on a standard 17 round P320 magazine, you can run it all day long in the P320 compact. If you're using a Carry grip module with your compact, then the TTI +5 base will mate up with the grip module. If you're using a Compact grip module, there will be a gap.

Now, the catch...

There are those who claim to have had issues with overinsertion of the magazine, and subsequent damaging of the ejector. Because the ejector is part of the fire control unit (FCU), if it's bent and damaged (and subsequently broken off), the FCU must be replaced, and that's the serialized part of the pistol. It's several hundred bucks. The solution is to not overinsert the magazine. If the slide is forward, there's no chance of overinsertion. If one just pushes up on the mag until it clicks, also no chance of overinsertion.

The baseplate on the P320 is designed such that it prevents overinsertion in the correct size frame. That is, the 17 rd. magazine can't be inserted too far in the carry or full size grip module. The 15 rd. compact can't be inserted too far in the compact grip module. A 17 rd. magazine can be pushed too far into the compact module, however, and so can the 21 round magazine.

The 21 round factory magazine has an extended baseplate that mates up with the carry or full size grip module, and prevents overinsertion. In a compact grip module it can be overinserted.

If you're careful, it's not a problem, and if you drive the magazine into place with the slide forward, it's still not a problem.

A possible solution, with the TTI baseplate on a 15 rd. compact mag, is to file a small notch in the frontstrap of the pistol grip frame, to allow the baseplate retention tab on the magazine baseplate somewhere to go. (there are other aftermarket devices that use a different form of retention for the baseplate, other than the push-pin on the TTI +5's

I just installed a Wilson compact grip module on my subcompact; it takes a 15 round magazine (same as the x-compact). I can put my 17 round magazines with the TTI +5 baseplate in just fine, and if locked in place in the grip module, they dont' quite contact the ejector. If one were to drive them home with the mag release depressed, or if the mag goes past that point, and the slide were locked back, then the ejector could be bent. I've never had that problem, but there are those who have reported it, so its worth considering.