Dear Mr. Rawles:
To amplify on some of your points is a recent reply to a reader letter, here is some data; Number 4 [bird] shot is .13 inch in diameter.
Number 4 buckshot (BK) is .24 inch in diameter and weighs 20.5 grains. (one pound avoirdupois is equal to 7,000 grains, 437.5 grains is equivalent to one ounce.)
OO BK is .33 inch in diameter and weighs 53 grains.
We have several levels of power in buckshot loads. Lets look at 12 gauge 2-3/4 and 3 inch shells.
2-3/4 inch standard OO BK has 9 pellets at 1,325 feet per second (FPS) at the muzzle.
Low Recoil 2-3/4 inch Magnum OO BK has 9 pellets at 1,125 FPS at the muzzle.
2-3/4 inch Magnum OO BK has 12 pellets at 1,290 FPS.
3 inch Magnum OO BK has 15 pellets at 1,210 FPS.
2-3/4 inch number 4 BK has 27 pellets at 1,325 FPS.
3 inch number 4 BK has 41 pellets at 1,210 FPS.
These velocities may very a little from one brand to another.
The 3 inch Magnums offer more pellets per load, but they recoil very heavily and reduce the magazine capacity. If I lived in an apartment, a mobile home or my exterior walls were thin or if I had other people living in my home, I would consider using no. 4 or no. 6 bird shot to reduce over penetration. You could always have the first and second shot to be bird shot and the last two or three shells buckshot. If I lived in a rural area and thought I might need more range and penetration then use OO BK or OOO BK and possibly shotgun slugs. Use the shotgun with buckshot at 30 yards and under, use shotgun slugs at 50 yards and under. There are specially choked and rifled barreled shotguns that will extend these ranges but the usual short barreled and bead front sight riot shotgun will be doing very good to achieve consistent hits at these ranges.
I load my 12 ga. house gun with (5) 2-3/4 inch Magnum OO BK (12 pellets) in the magazine with a empty chamber, and 5 more of the same shells in the buttstock shell holder. Close by I have a ammo belt with 20 shot shells (bird shot,buckshot and slugs).
As a comparison – if fired from a rifle the 22 long rifle with a 40 grain lead round nose has a muzzle velocity of 1,255 to 1,280 FPS.
Each number 4 BK pellet will have a little less energy than a 22 long rifle bullet and each OO BK pellet will have a little more energy than the 22 long rifle bullet at the muzzle. Consider several people with veering levels of skill firing at a target with a 22 long rifle all at the same time, at close range this buckshot ammunition is very effective. Thank you for your work. – Campfire