Just to let you know, the night sights are 6.9 mm which is what comes on the G21 from the factory.
Certified Glock Armorer
G17RTF2/G, G19RTF2/G, G22RTF2/G X2, G23RTF2/G, G23CRTF2/G, G31C RTF2/G Custom
G17, G19, G20, G21C, G22C, G26 X2, G27, G32, G33 All Gen 3.
Ruger Security Six .357 Mag.
Ruger Super Blackhawk .44 Mag.