There are any number of factors influencing buckshot performance, but here are a few that seem to be more important-
1) Hard lead alloy and/or plated buckshot pellets. They tend to deform less on firing and being forced down the bore, and rounder pellets tend to fly straighter and thus tend to pattern better.
2) Grex (granulated plastic filler) or some other protection between the individual pellets inside the shotgun shell. Again, this helps deliver rounder, less deformed pellets out of the muzzle.
3) A shot cup or similar layer between the pellets and the inside of the barrel. As mentioned, this offers another layer of protection to the pellets.
I've found that in general, less expensive brands of buckshot (S&B, RIO etc) tend to be loaded with soft lead, unprotected pellets - and this produce the widest patterns.
The 'standard' loads from major manufacturers tend to offer grex filling inside a plastic shot cup, collar or one piece wad, and sometimes harder alloy or plated pellets (like Fiocchi), and tend to deliver medium size patterns.
The 'premium' loads (Federal, Hornady, Speer) offer hard lead plated pellets, generous amounts of grex, and a thick-walled shot cup with a good bit of room inside. This shot cup, known as a FliteControl wad, tends to hold pellets together until the whole cup exits from the muzzle, at which time the wad is retarded and the pattern continues downrange with pellets in close proximity. These loads tend to produce the tightest possible patterns from open choked shotguns.
I'm fine with 2 3/4" full velocity 9 pellet 00 buck, right now I'm using Federal LE-127 00. It has the FliteControl wad, and out of my favorite 18" CYL bore 870 it will print 4" patterns at 25 yards. I like tight patterns...
The sidesaddle is loaded with Brenneke KO slugs, in case I need more penetration than buckshot can deliver.
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