Summary
With the right load, a shotgun can be very effective in quickly stopping the deadly violence being perpetrated by a criminal who's invaded your home.
...With birdshot you are wise to keep in mind that your gunfire has the potential to NOT PRODUCE an effective wound. Do not expect birdshot to have any decisive effect.
Number 1 buckshot has the potential to produce more effective wound trauma than either #00 or #000 buck, without the accompanying risk of over-penetration. The IWBA believes, with very good reason, that number 1 buckshot is the shotshell load of choice for quickly stopping deadly criminal violence.
End Notes
The term "Magnum" when applied to shotshells means "more shot." Magnum shotshells usually propel their pellets at a lower velocity than a standard shotshell.
Shotgun barrel length does not affect our shotshell recommendions.
References
Cotey, Gus J.: "Number 1 Buckshot, the Number 1 Choice." Wound Ballistics Review, 2(4), 10-18, 1996.
MacPherson, Duncan: "Technical Comment on Buckshot Loads." Wound Ballistics Review, 2(4), 19-21, 1996.
MacPherson, Duncan: Bullet Penetration, Ballistic Publications, El Segundo, California, 1994.
DiMaio, Vincent J.M.: Gunshot Wounds, Elsevier Science Publishing Co., Inc., New York, New York, 1985, pp. 163-208