palm swelln.Firearms a protrusion on the grip of a firearm contoured to fit the shape of the hand.
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1986 Shooting Life Autumn 92/2 The full pistol grip has a palm swell, although unlike some this is a sensible size and not so massive as to defy a proper grip.
1993 Air Gunner Nov. 49/1 A good palm swell and chequering on the pistol grip aids right-hand control.