Why? I want a pattern if I'm grabbing a shotgun.
Choices are good. I'm in favor of them.
I use a shotgun as a short range defensive weapon because it's the largest caliber long gun I can easily handle, and it fires payloads measured in ounces not grains. As Clint Smith says, I like shotguns because they will remove meat and bone from a target. I choose shotguns for their terminal effect, not to make up for my own shortcomings at delivering the payload on target. It's my job to hit what I shoot at, it's the shotgun's job to neutralize what I hit. A minimum of research into the history of fighting shotguns will provide more than adequate evidence as to their efficiency as fight stoppers when used properly.
My choice is for tight patterns even in a plain ordinary joe citizen defensive shotgun. I want to get as much useful range out of buckshot as I can before I have to switch to slugs. In the terms many shotgun trainers use, I want to extend my 'A zone' to the point that I can eliminate the 'B zone' completely.
It's my conclusion that buckshot pellets can run out of sufficient energy to do the job before they run out of pattern in some cases, and I don't want to push my luck at ranges much longer than 25 yards with buckshot no matter how well it patterns.
The load and barrel I use allows me to extend my A zone out to 25 yards or so, at which point I will likely be switching to slugs anyway if circumstances permit.
That has nothing to do with police needs, or military needs, or anyone else's needs. That's my choice based on my own training and experience.
YMMV of course.
lpl
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http://www.officer.com/print/Law-Enforcement-Technology/In-defense-of-the-shotgun/1$40875
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Patterning
Patterning is how you determine the spread of the buckshot as the range increases. It is the first step in understanding how your weapon will perform with buckshot. To pattern, fire single rounds at paper targets from 5, 7, 10, 15, 20, 25 and 30 yards. Knowing how the gun patterns is a very important part of training and should be the first thing taught to shotgun shooters.
A shotgun has three levels of use typically referred to as zones. The A zone is where the shotgun is a truly devastating weapon. It's measured from the muzzle out to where the buckshot pattern stays together so that it makes one big ugly hole in the target; this hole can be covered with your open hand. Depending on the weapon/ammo combination, the A zone is out to around 7 to 10 yards.
The B zone is where the pellets have had time to spread out and develop a pattern but are still on target. This is the zone where the shotgun is most effective and can be exploited to the fullest. The weapon can be fired quickly with a flash sight picture and still make good hits. The B zone goes from about 10 to 20 yards. Inside 20 yards, the shotgun loaded with 00 buckshot is king, but if you need to engage a target at more than 20 yards and you only have 00 buck, the rifle is the way to go.
The C zone is the point at which the pellets spread out and some may be off the target. While still lethal, the loss of control of the pattern makes the use of buckshot unacceptable for law enforcement.
Advances in modern ammunition have a huge effect on how a shotgun patterns. Simply changing ammunition can reduce the spread of the pattern by 50 percent. Each gun and ammunition combination will also pattern differently. It is important that the gun be patterned using the same ammunition that is carried on duty so that an officer can be certain of how the gun will perform in combat.
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sigh
And I think that the slug will drop sooner from a 30 inch barrel as I think that it is longer than it takes to reach max velocity so it may actually be going slower than from a 20-22 incher... But, as usual, I could well be wrong.