Majestic Arms has been helping Ruger MK2/3 owners with their upgrades. Well now they have turned their attention to the Ruger MK4.
Their master grade kit features all the same upgrades as before just without the speed strip feature. One aspect of the Master Kit is in the hammer. It has recesses to allow the user to keep the factory magazine safety disconnect or omit it entirely. Due to certain youth marksmanship programs, removing the factory magazine safety can disqualify a shooter. Majestic has thought of this and made modifications to their design.
The next upgrade is a barrel bushing to improve barrel to receiver fit. The factory Ruger bushing is a rubber o-ring and after time deteriorates rather quickly. Majestic has improved with with their own machined bushing. There are two set screws, one on either side that hold the bushing in place. The bushing itself has a small set screw that adjusts the height. The bushing should be good for several hundred shots before you may need to check the fit of the bushing. It can simply be readjusted and serviceable for another several hundred rounds. They are calling it the Bank Vault Locking Block.