Why is it that we use hard cast bullets for heavy big bore applications like bear defense etc? Wouldn't a 320 gr 44 mag fmj work just as well as a hard cast? (Assuming similar flat nosed bullet construction)

And if the hard cast has some advantage I don't know about, why don't you see it in smaller calibers, like say 9mm hard cast instead of fmj?

I'm sure there is something I'm missing here, just not sure what it is

Thanks!

A hard cast bullet has a lower co-efficient of friction than a jacketed bullet.  So you can push it a little faster without raising pressures.

In lesser cartridges, the same is true, but most people prefer JHPs in 9mm, and if you want penetration, the FMJ does pretty good.

Tradition also plays a part.  Think of Elmer Keith for example.

The market for anti-bear ammunition is really small.  Consequently it can easily be met with cast bullets.  If bears ever started invading in large numbers we might see ammo factories crank up heavy FMJ loads, but right now it is just as easy to use cast.

The .44 Special was loaded with black powder and round nose full metal jacket bullets over a century ago.  Apparently people preferred lead in their wheel-guns, and they went back to lead.

I shoot hard cast lead from all my handguns, and most of my rifles.

Hunters have historically wanted a big flat nosed lead bullet for hunting.  This is easy to come by in lead, but far less common in jacketed.  With the lead, you can control the alloy a great deal, and to a somewhat lesser extent the velocity to control expansion.  FMJ at pistol velocities, you are pretty much stuck w/ non expanding, and often a less effective round nose.  That may or may not be OK for your application.

I prefer lead in my 9mm, .32 auto, .32L, .45auto, .38's and .357  So I dunno what to tell you about "nobody uses hard cast lead in 9mm."  Sure they do.  I do.  I'm not alone.

Any time I run low on ammo, I just warm up the lead pot, and cast the exact sort of bullet I think I need.  Making your own jacketed slugs is much more involved, and serves no purpose in the pistol calibers I use.

My bear defense is a Garcia Bear Canister and maybe pepperspray.

The advantage of lead in 9mm:
Zero barrel wear.
Slightly increased speed w/ same powder charge
More expedient nose geometry WRT game effect
Low cost
Accurate
Home made
Lead does very well at low velocities, Jacketed can be truly dangerous at slow speeds (obstructed bore)
More shooting for the same money

Not only is hardcast have a lower coefficient of friction, they are also softer than gilding metal. The hardest, hard cast is Linotype. That rates as a 22 on the Brinell hardness scale. Gilding metal rates 100 on the same brinell hardness scale. If a bullet is softer, it takes less effort to push down the barrel. If it takes lass effort, more powder can be used to make the bullet go faster, resulting in more energy.