The tighter the choke you use, the longer and narrower the shot cluster will be as it leaves the barrel, and the more “drafting” pellets that will remain in the pattern core. The load will also pattern more tightly in thin air that in heavier air due to the lower air resistance. Air is not uniformly dense—it’s denser at sea level than at high altitude, and cold air is denser than hot air. The difference may not be much, but it’s no coincidence that the record shot pattern (most pellets in a 3-inch circle) was shot in the thin air of a hot, dry day. Hedge your bets in the cold, dense air of late-season by shooting high-velocity loads or by choosing one size larger shot than you ordinarily would.