BudsGunShop.com - Will it accept a 21rd magazine?

I personally have put the 15rd in my subcompact grip, and I have read where if the same caliber they are interchangeable. Of course you cannot put a smaller one in a big grip, ie: 12rd or 15rd in a full size that takes a 21rd..
I purchased the P320 Compact which came with 2 15rd mags, then bought a subcompact grip module on ebay and a 12rd mag from buds (where I got the gun). It works great. I carry it daily with the subcompact grip and 12rd mag, just throw the 15rd mags in at the range.

Check out mec-gar mags. The 20 round for the p226 is almost flush, so they may make one for the 320 also.

Yes it will accept a higher capacity magazine. It may stick out the bottom depending on the gun and the brand of the magazine, but yes this gun will accept higher capacity magazines.