But guns are special

[jimmy the one]

110. balked on the wall challenge

ezra: I thought it was a given that we are discussing centerfires, but rimfires are a good topic to bring up. And yes, 40gr and 55gr .223 JHP penetrate less than or equal to typical .22LR in both drywall and gelatin.

Appears to be so, but other considerations are, which would cause more damage if they hit someone - the most severe damage would occur of course after the first wall. And if the .223 were to fragment, tho doesn't as much, if only rarely, as at greater distance, there would be effectively two bullets to contend with.
As you stated: Now, in terms of damage to the target, there is no question; .223 and .357 create a *wider* wound than .22LR, by a large margin, and .223 *FMJ* will penetrate more than most .22LR.

again here is what you originally wrote: They {ar15's} are an excellent choice of defensive long gun for the home, offering almost as much effectiveness as a shotgun with less hazard to neighbors/bystanders than buckshot or handgun rounds.

Define bystanders. If you meant they were in an adjoining room, not sure they'd be classified as bystanders, but house occupants.
Of course the ar15 is more wieldly than a handgun, which can be better controlled nearer the body, & less susceptible to bumping into things or getting bumped by things (like opponents parrying arms).
I guess a front metal door isn't as safe as a wooden one anymore (the .223 would penetrate it readily, not so much handgun bullets) if you have ar15's in the neighborhood.

I wrote: "By default I assume you agree that ar15s rank very low regarding defensive gun uses. That is actual usage..'
ezra wrote: Not sure what you're arguing here

That is, as low as the ar15 ranks in committing homicide & violent crime, it also ranks low in being used in a defensive gun use (dgu), by rate as well as total index compared to other 'popular' firearms, as you call it.

I wrote: I will stand behind a drywall & paneling & be shot at by a 22 rimfire, you stand behind it & get shot at by an ar15. "
ezra wrote: If you were standing behind the third "wall" in this test, which would you rather be shot at with? The .223 loads that didn't penetrate the third wall, or the 9mm/.380/00 buckshot loads that did?

That wasn't the question; you answered a question with a question. Try again.
What about 9mm & .38, & dirty harry's., or a 25 caliber cf acp, or 25 cal rf (if they make them).

ezra: A basic Smith & Wesson or Ruger AR will set you back about $550 if you shop around, $600 if you don't

You're either low balling or know people in the black market, or it's bottomed out again: june 2013 It appears that the market for the popular rifle has bottomed out. The average price of an AR-15 has in recent weeks returned to the $800-$1,050 range, down from its all-time high of $2,500 (averaged), according to the gun blog The Truth About Guns

ezra: I thought it was a given that we are discussing centerfires, but rimfires are a good topic to bring up

Actually you brought up rimfires first, in the very post 75, so I dunno about what you say:

post 75: AR's dominate smaller game hunting (varmint hunting, predator hunting) down to the level at which .22 rimfires take over. They are an excellent choice of defensive long gun for the home, offering almost as much effectiveness as a shotgun with less hazard to neighbors/bystanders than buckshot or handgun rounds.