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Gun Information: Shot Size, Weight of shot, Bore Size, Spread Pattern and Chokes:*

Shot sizes (in portions of an inch)
no. 12 11 10 9 8 7.5 6 5 4 2 Air BB 4buck 3buck 1buck 0buck 00buck
Dia. .05" .06" .07" .08" .09" .095" .11" .12" .13" .15" .175" .18" .24" .25" .30" .32" .33"
#/ oz 2385 1380 870 585 410 350 225 170 135 90 175 118 21 19 11 9 8
The business end of the shotgun shell, and of the shotgun itself is the shot. Fired out in a pattern, like a cloud of lead, the different sizes have their own strengths and weaknesses. The smaller the shot size, the more densely packed the shot can be, giving a higher weight of shot. This higher weight of shot does little good except at shorter ranges, as the smaller shot sizes do not penetrate or hold their energy as well as the larger sizes. Buck shot, that legendary icon of lethality, is the same diameter as a standard thirty caliber rifle. Buck shot will penetrate like a bullet at the closer ranges, and will hold it's energy out to 50 yards and maybe a bit beyond. Of course, a cartridge filled with 00 buck might only have ten or twelve balls in it, negating much of the advantage of the multiple projectile "lead cloud" effect for which the shotgun is known. At greater ranges, it is possible for the target to slip between the pellets, as at longer ranges there may be as much as several inches of space between each of them.
    The largest shotgun projectiles are slugs, which essentially turn the shotgun into a large caliber, low velocity rifle. The term rifle may seem a bit out of place here, since part of the BATF definition of a shotgun includes the provision of a smooth, non rifled bore. In the case of the shotgun firing slugs, it is the projectile itself that is rifled so that it takes on a spin as it moves through the bore, and through the air. Though slow moving, this miniature artillery can have devastating effects upon the "target".
Weight of Shot

10 Gauge 12 Gauge 16 Gauge 20 Gauge 28 Gauge .410 gauge
Slug 1.75 oz. 1.25 oz. .8 oz. .75 oz. .5 oz. .2 oz.
00buck 18 pellets 15 pellets ******* ****** ****** ******
4 buck 54 pellets 41 pellets 18 pellets 15 pellets ****** ******
4, 6 2.25 oz. 2 oz. 1.25 oz. 1 oz. .8 oz. .5 oz.
BB, 2, 4 2 oz. 1.85 oz. 1.15 oz. ****** ****** ******

Bore Sizes (in portions of an inch)
10 Gauge 12 Gauge 16 Gauge 20 Gauge 28 Gauge 410 Gauge
.775" .725" .662" .615" .550" .410"
The original bore size designation was a continuation of the old English method to determine the hitting power of cannon and other ordnance. This was done by determining weight of throw rather than measuring the bore size directly. Thus cannons were called "two pounders" or "six pounders" according to the weight of a ball which would fit down their bore.  As weight was much easier to measure precisely at this time, than size, this was an easier system to use. Since the weight of fire was often the determining factor in the outcome of naval battles, and since knowing the weight of munitions required was of great convenience to quartermasters, this system was in use up to the time of the rifled, breech loading cannon, and even a bit beyond. The breech loading cannon, with it's conical projectiles, and self contained shells, made the old weight of throw system irrelevant. A shotgun bore describes the number of balls, equal in diameter to that of the bore, it would take to make one pound. In the case of the ten gauge, it would take ten balls of .775" (The size of a ten gauge bore) diameter to equal one pound. The exception to this rule is the .410, which is technically a caliber rather than a bore. The largest bore made in any quantity these days is that of the ten gauge, though eight, and even six bore guns have been made in the past.

Spread Patterns for Various Chokes (30"@40 yds.)
Full Modified Improved Cylinder
70% 60% 50% 40%
A shotgun choke, is a change in the shape, angle, or diameter of a portion of the barrel, in an effort to control the spread or pattern of the shot. The rule of thumb for shot spread is 1 inch of spread for every 1 yard of distance. This is close enough to the truth to be a useful tool in calculating pattern spread and hitting power at various ranges. It may also be seen that this is quite a contrast to the depiction's in movies where a shotgun is fired and everything in front of it and off to both sides of it is blasted and destroyed. A shotgun is considered to be a 50 to 100 yard weapon, putting it in the same class as the pistol. The range depends somewhat on the shot sizes loaded, and on the type of choke. The 40 yard standard for measuring choke pattern is a reflection of the traditional 40 yard range considered to be the maximum back before better shells, and chokes were developed.
    In construction, the choke may be a constriction, expansion, bell, or widening of a section of the bore. In modern practice, the choke tends to be a slight constriction at the end of the bore, though in some cases there is a slight expansion right before the constriction. Needless to say, slugs should not be used in anything other than a special slug barrel or cylinder choke, where there is no constriction. At the very least, the choke and maybe the entire barrel will be ruined. At worse, pressure could rise to the level where injury might occur.
Some typical choke diameters

Full Modified Improved Cylinder
10 Gauge (.775) .740 .758 .768 .775
12 Gauge (.725) .695 .710 .719 .725
16 Gauge (.662) .638 .650 .657 .662
20 Gauge (.615) .594 .605 .611 .615
28 Gauge (.550) .533 .542 .547 .550
.410 (.410) .396 .405 .408 .410

 

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