P320 is modular chassis: Trigger group is legal firearm: has serial. Everything else is modular/swapable without FFL: calibers slide size, frame sizes. Have many gun configurations, register only one ( for those in restricted parts). Caliber x-change kits are avail for $350ish, have everything you neeed sans trigger module-even (should) include a magazine.
This is the gun the Army gave the contract to. They had drop issue, these have been sent back to Sig and upgraded: safe now.
But wait, There is MORE. This is the good part.
The trigger module is the registered part, the rest of the stuff is on ebay, mail order, etc. Trigger module Needs FFL transfer and master's blessing>>>>but you can make your own trigger module without the FFL ( in non-commie land). Just like 80% AR-15 receivers, they have 80% trigger modules and jigs for finishing : drill holes, bend and file rail ears.
- Jig is $150: share cost with buds/ make it a group thing
- blank module is $100
- genuine Guts are $210-$250 - can be tough to find. ebay now.
- x-Caliber cnversion kit $320+
drill press, vise, drills, time, patience
These will not be available forever. I would bet my left testicle.