The standard 12 gauge [or *gage* if you prefer the US Army spelling] load for a shotgun is the 9-pellet M162 OO buckshot round, each pellet being about .33 caliber in diameter. Muzzle velocity from the military 12-gage load runs around 1,450 FPS from a military-standard 20-inch barrellede shotgun.
The Winchester commercial equivalent is their 12 Gauge, 2-3/4" LG., SUPER X, BUCKSHOT, 00 BUCK, 9 PELLETS, # XB1200. Their Reduced Recoil OO Buck load is the Winchester 12 GUAGE, 00 BUCK, 9 PELLET, REDUCED RECOIL, #RA12005.
Remington does things a little differently: their reduced recoil OO Buck offering is the Remington 12 Gauge, 2-3/4" , MAX DR., BUCKSHOT, REDUCED RECOIL, 00 BUCK, 8 PELLETS, # RR128B00. Their full-power OO buck loading is the Remington 12 GAUGE, 2-3/4" LG., MAX DR., BUCKSHOT, 00 BUCK, 9 PELLETS, # 12BK00.
Moving on to the #1 buckshot loads, there are generally two power levels available: the standard 16-pellet load carrying 16 pellets of approximately .30 caliber, or the 2¾-inch magnum load which uses 20 of the .30 pellets.
The Remington 16-pellet load is Remington 12 Gauge, 2-3/4" , MAX DR., BUCKSHOT 16 PELLETS, HIGH POWER, # 12B1.
As for the effectiveness of the various loads, that depends to a large extent on which one offers the best pattern in your particular gun at the range at which you expect to use it: I use 20-pellet #1 loads in one of my shotguns, 8-pellet Remington low-recoil *lites* in a second, and standard M162 OO Buckshot in the other two...because those loads work best in those particular guns.
As for which is most useful from the standpoint of wound ballistics effectiveness, this 10-year-old Tactical Brief from the Firearms Tactical Institute is still pretty much valid, though the 20-pellet #1 buckshot loads are pretty hard to locate nowadays.
"12 Gauge Shotshell Ammunition
For personal defense and law enforcement applications, the International Wound Ballistics Association advocates number 1 buckshot as being superior to all other buckshot sizes.
Number 1 buck is the smallest diameter shot that reliably and consistently penetrates more than 12 inches of standard ordnance gelatin when fired at typical shotgun engagement distances. A standard 2 ¾-inch 12 gauge shotshell contains 16 pellets of #1 buck. The total combined cross sectional area of the 16 pellets is 1.13 square inches. Compared to the total combined cross sectional area of the nine pellets in a standard #00 (double-aught) buck shotshell (0.77 square inches), the # 1 buck shotshell has the capacity to produce over 30 percent more potentially effective wound trauma.
In all shotshell loads, number 1 buckshot produces more potentially effective wound trauma than either #00 or #000 buck. In addition, number 1 buck is less likely to over-penetrate and exit an attacker's body.
For home defense applications a standard velocity 2 ¾-inch #1 buck shotshell (16 pellet payload) from Federal, Remington or Winchester is your best choice. We feel the Federal Classic 2 ¾-inch #1 buck load (F127) is slightly better than the same loads offered by Remington and Winchester. The Federal shotshell uses both a plastic shot cup and granulated plastic shot buffer to minimize post-ignition pellet deformation, whereas the Remington and Winchester loads do not.
Second best choice is Winchester's 2 ¾-inch Magnum #1 buck shotshell, which is loaded with 20 pieces of copper-plated, buffered, hardened lead #1 buckshot. For those of you who are concerned about a tight shot pattern, this shotshell will probably give you the best patterning results in number 1 buck. This load may not be a good choice for those who are recoil sensitive.
Third choice is any standard or reduced recoil 2 ¾-inch #00 lead buckshot load from Winchester, Remington or Federal.
If you choose a reduced recoil load or any load containing hardened Magnum #00 buckshot you increase the risk of over-penetration because these innovations assist in maintaining pellet shape integrity. Round pellets have better sectional density for deeper penetration than deformed pellets.
Fourth choice is any 2 ¾-inch Magnum shotshell that is loaded with hardened, plated and buffered #4 buckshot. The Magnum cartridge has the lowest velocity, and the lower velocity will help to minimize pellet deformation on impact. The hardened buckshot and buffering granules also help to minimize pellet deformation too. These three innovations help to maximize pellet penetration. Number 4 hardened buckshot is a marginal performer. Some of the hardened buckshot will penetrate at least 12 inches deep and some will not."