To kill grizzly and coastal brown bears reasonably quickly when shooting head-on into their thoracic cavities, what penetration in inches or a metric length is required to avoid running into serious "issues"? Does this depth of penetration remain constant for bow hunters' arrows? If firearms and arrows can do the job mentioned but require different penetration depths, which requires more depth? Why?

No expert and can’t give you exact measurements but a good rule of thumb is a pass through would be preferable. Two holes are better than one

Though it surely can be done and probably has been, I want no part of shooting an arrow head on into the thoracic cavity of a large brown bear and hoping not to run into serious “issues.”
I’ll take a 458 sized hole from entry through the top of the heart and either out his rear or way back into the nasty stuff please. If I Gould break his pelvis on the trip even better.

Running into serious issue?? Lol well......don’t matter what you shoot them with or what penetration you get. A bear without a heart lung AND liver still has time to tear you a new one. Broken bones or a off switch on the CNS is all that will keep you from possibilities of serious issue.
In inches...every bear is different in size so no number can answer that. But no matter what you gotta ruin his vitals. I’d plan on at least two feet of penetration for an arrow. A bullet four feet. If you absolutely must have a number.

18 inches !

In the best circumstances just enough to destroy the necessary tissue to kill the bear.

On a side brain shot heck 8 inches would work just fine.

Under the worse circumstances 4 feet as Jake says is good.

Arrows use a whole different killing method. And real do not have any bone breaking ability.

Place a sharp broad head through the heart or both lungs dead critter. If you can brain or spine them with a arrow same results.

But counting on a arrow to smash through bone is very iffy.

quote:

Originally posted by 458Win:
18 inches !

Phil I heard the 9mm only gets 17 inches??!!

Next time I'm bringin the 500 Jeffery, not cause it's needed just because I want to. A 570g TSX at 2300 fps should penetrate just fine.

quote:

Originally posted by chuck375:
Next time I'm bringin the 500 Jeffery, not cause it's needed just because I want to. A 570g TSX at 2300 fps should penetrate just fine.

on the light side but doable lol ...

quote:

Necessary penetration for coastal brown bears?

Wear a condom, the bear will never feel it....

Or to quote from a USNavy UCMJ article: Penetration, however slight, is sufficient to complete the offense.

Sorry, couldn't resist. I crack myself up...

Phil sez 18 inches, if anyone knows. it just has to be Phil, he has shot and been in more bear kills than anyone else that I know of.

.Ive shot enough DG in Africa to believe 18 inches would work on anything under those circumstance short of elephant I suspect wherein I would prefer at least 3 feet of penetration, to cover all circumstances, much prefer 6 feet on elephant, Hippoo and buffalo, In fact a good rule of thumb for me has been a bullet that will penetrate the animal hunted almost from stem to stern.but that's a different scenario than the Poster required. His shot and angle is just to the vitals from a specific angle..My post considers the going south shots after a less than instant killing shot on buff etcf, which is much more likely than an instant kill.

But Im going to be packing a rifle of large caliber in the first place under my present circumstances..I won't be there unless IM hunting or fishing...