Although the Gen4 changes operate nicely on many of the Glock body dimensions, they really shine for the extremes, namely, the biggest body types (G20 and G21) plus the smallest (Subcompacts). In the case from the significant-hitting 10 mm G20 and .45 ACP G21, the twin-spring recoil assembly nicely decreases the level of felt recoil. Attaining a si