Sorry, I don't know about this, but I hope someone does. Its an interesting idea. I'd be willing to pay plenty for pre-ban high-capacity 9mm mags for a USP Compact, but I don't think they exist. I wonder if it would be legal to do this? The magazines are legal. The ammo is legal. The gun is legal. But is the combination legal? Who knows. I hope someone checks this out and replies.