After seeing the doggone thing misquoted, improperly mentioned, and otherwise abused by those who heard of it, but never actually read it, I dug out my copy of the USFS bear gun report and extracted the salient points. Hope you find it interesting.
Meehan, W.R, and J.F. Thilenius. 1983. Safety in bear
country:
protective measures and bullet performance at short range.
USDA, USFS, Pac. Northw. For. And Range Exp. Sta.,
Gen. Tech. Rep. PNW-152. 16pp.
They used standard OTS rifles (and shotguns) and ammo, and did not test any calibers that were wildcats or weren't commonly available in AK gun stores. Their determinants of suitability (3 shots fired) were striking energy (KE), penetration, remaining bullet weight, and bullet expansion in Hagel's preferred medium of moistened 50% fine silt and 50% sawdust. Each category counted equally "because we had no way to determine the relative importance of each ballistic category." All shots were fired at 15 yards.
The first 5 long gun results were in order of suitability:
Caliber, bullet
wt., bullet shape,
mfr.
.458 Win. Mag w/ 510 gr. RSP,
W-W
.460 Wby. Mag w/ 500 gr
RSP,
Wby
.375 H&H Mag, w/ 300 gr.
SSP (semi-pointed SP), W-W
.338 Win. Mag w/ 300 gr. RSP,
W-W
.375 H&H Mag, w/ 270 gr.
RSP,
R-P
The .45-70 clocked in at 17th with a 300 gr. Hollow point by Federal.
The 12 ga 2 3/4" 1-ounce slug came in at 26th.
For handguns, the first 6 were all variations of .44 Rem. Mag. 240 gr. (Overall at 32nd place) and "should not be considered a primary weapon for protection from bears."
Number 7 was the .357 158 gr. JSP and the overall caveat was "We do not recommend them {my note: 44 S&W, .45 Auto, .45 Colt, .41 Rem. Mag.}, even for back up protection. The exception may be the .41 Rem Mag. We were unable to obtain the high-velocity jacketed 210-gr bullet factory load for our tests."
For sights on the rifle, they recommended large aperture peeps followed by express sights, and recommended against standard, narrow-notch open sights and scopes. They also emphasize that the sling be removed and the rifle carried ready for action in the dense alders of brown bear country.
They really equivocated on warning shots. They note that it is purely personal choice. You might "antagonize the bear and precipitate a charge" and you will have "one less cartridge in the rifle."
And finally, "The most important shot is the first one. If not properly placed, it may also be the last shot fired. If a bear goes down on the first shot, continue to shoot. Do not stop to observe the effects of the shots . . . If the bear is still active and the rifle is empty . . . reload and continue to try to kill it."