I had fitted factory spare MX12 Prosport barrels to my MX8 action but barrels aren't interchangeable - they need fitting and the fore-end has to stay with the barrels. Trigger groups have to be shaved to fit and I've seen more than one stock split when fitted to the same model. To put it another way - if you have 4 Perazzi droplock, only the stocks interchange, not even the fore-ends will swap about without re-fitting. These are bench-fitted guns. MX12 stocks obviously have a different inlet for the triggerplate to MX8 which gives them a stronger grip or potential for a slimmer grip. For those who don't know, MX12 have non-removable coil-spring triggers which allow an elegant way of switching to top barrel first. But do not dispair - once you've got your spare trigger group it only takes seconds to swap every time the V-spring snaps. Then you've got the gun that 14 of the top 15 used in Beijing.