Okay, so for approximately the last 70 years (the earliest references to it that I know of are from 30's comic books, but they may go back earlier to the invention of the hollowpoint in the 1880s) there has been this idea that "filling your bullets with mercury will make them explode inside someone", or some such thing.
Time for a bit more firearms mythbusting.
An incompressible liquid, encapsulated in the nose of any bullet, in a jacket that is structurally weaker than the force being applied to it (pretty much any possible hollowpoint) will cause the nose of said bullet to burst apart radically on impact with a hard surface (which at high velocities includes human flesh).
The effect is similar to plastic ballistic tips in modern spitzer bullets, but would be more radical as the sealed chamber of the bullets nose exceeded it’s structural limits and burst. This may cause fragmentation, or may simply cause radical expansion, depending on the construction of the bullet, and impact velocity.
Whether this fluid is mercury, or water, it doesn’t mater; all would have a similar effect. That effect may in fact be useful for creating bullets that feed well in guns that wouldnt otherwise feed hollowpoints but would still expand; or in states where hollowpoints arent allowed; or in situations where a hollowpoint might be clogged up with foreign matter preventing expansion. The CorBon pow'r'ball operates in a similar manner, as do the new expanding FMJ bullets from several manufactures.
That however isnt' what people are thinking of when they talk about mercury tpped bullets. The MYTH that most people think about with exploding bullets would involve mercury fulminate (a priming compound). Assuming that the bullets didn’t detonate in the chamber from the shock of ignition, the fulminate would create a small explosion on impact with a hard surface (and again, at a high enough velocity that includes human flesh).
That explosion would almost certainly cause fragmentation of the bullet, but is unlikely to significantly enhance the damage in human flesh that bullet would cause.
Up until the 70’s there were bullets available for handloaders that had a stable priming compound sealed in the nose. The reason they stopped making them was because the ATF ruled them to be destructive devices, and each one carried a DD fee attached to it (essentially they treated them like cannon shells).
The gun store I worked at had several cases stored since that time, and we did various experiments with them, including loading and firing, to determine their properties before destroying them.
The primary effect was to make distant impact much more visible. They were in fact very fun to shoot at distant rocks etc… They wouldn’t detonate on paper targets, but did on milk jugs, stacks of newspapers, phonebooks and the like. When they detonated the resulting damage was no different than a bullet which fragmented naturally.
You could do the same thing with tannerite today (assuming you shot the loaded rounds within a few days of mixing. Tannerites explosive properties degrade over time); I don’t know if it would be legal or not (I suspect not), and as to how safe it would be… well I don’t know. I wouldnt do it myself anyway. I had a gun blow up in my hands once, I dont want it to happen again.
The small quantity of explosive a pistol or rifle caliber bullet could hold without causing stability issues, wouldnt do all that much anyway. It may destroy the bullet and cause radical fragmentation, which although it creates messy wounds, generally casuses LESS dangerous wounds unless significant penetration occurs before fragmentation (as happens with high velocity rifle rounds); in which case the wounding IS far more severe. So if it caused significant fragmentation in high velocity rifle bullets, where penetration was adequate, but fragementation wouldnt otherwise occur (say a 5.56n round traveling at under 2250fps)then it may be worthwhile, but otherwise such a round would in fact be less effective
Now if you did the same thing with say, chemically pure sodium... well that might have some kind of nasty reaction in someones body, though again because of the small quantities involved, probably no more explosive than any fluid, or a primer would be.
Of course you can fill the core of the round with white phosphorous, which if ignitable by the firing of the cartridge makes a tracer; and which DOES do somewhat more damage on impact than a normal bullet, in that it can very easily set fires.
Perhaps a hollow slug from a shotgun, when filled with a stable explosive would work well; but that would certainly be classified as a destructive device by the ATF.
Every once in a while I hear about some idiot who epoxies primers, or percussion caps, into his hollowpoints. So far the only result I’ve heard of is them blowing up their guns.
One thing you CAN do that is legal, and safe, is to epoxy lighter flints into the nose of your hollowpoints. This was suggested by John Ross in unintended consequences, and jsut for gits and shiggles I tried it. It makes the bullets I tried it with somewhat unstable at longer ranges, but you very definitely see a spark when you hit a rock or a metal plate.
