The Glock 21 DEFINITELY has less felt recoil than the SigSauer P220. The Glock 30 has less felt recoil than the Sig P220. (I have both, in fact, I've had two Sig P220s, both European & American models.) Not that this is a real problem, since the .45acp is a very gently-recoiling round in many loadings, but there IS a difference in felt recoil between guns shooting a given cartridge, depending upon the weight of the gun overall, the mass of the reciprocating parts, the elasticity of the gun frame, and the degree of leverage which the barrel is capable of exerting on the gun as a whole, during firing.
The Sig P220 is a fine gun, and though people post on this and other lists about their lower durability than, say, Glocks, I've never had anything break or otherwise "go south" on mine, and I've had 'em, carried 'em, and shot 'em for 15 years. They are very precise guns, comparatively, probably due to their tighter-than-other-guns' tolerances, yet very reliable. Mine have always fed everything, including Speer's Lawman 200 gr hollowpoint dubbed "the flying ashtray".
The Sig's problems, however, as compared to the Glock, are:
1.) It's DA/SA, that is, double action first shot, subsequent shots single action, and,
2.) Its bore axis is too high (attributable to the rather-too-bulky DA/SA mechanism housed in the frame), and the gun therefore exibits more muzzle flip (an aspect of "felt recoil") than guns with a lower bore axis, like the Glock.
That said, the SigSauer P220 is considerably more compact in ALL dimensions than the Glock 21, with width being the most noticeable of those dimensional differences. They would both be excellent home defense guns, with the Glock 21 being the definite winner in this role, IMNSHO. If you intend to ever use the gun for CCW, however, the P220 would be the obvious choice, as the Glock 21 is hard to conceal unless you're fairly large-statured. Have you considered the Glock 30 as a compromise choice? Good luck to you.
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