When it comes to getting more and more energy into a target (forget "energy dump" notions that quantize this; I'm simply talking about how disrupting more 'stuff' than a weaker bullet will require more power to work with) going
heavier is an extremely inefficient route
1) Recoil mounts exponentially, to the point the gun is useless after one round
2) Even small diameter rounds will fully penetrate, so the only gains are to the diameter of the wound which are not commensurate with the increase in recoil & energy required to obtain them
3) Bigger bullet makes everything else about the gun bigger & expensive
The one major pro is that a larger bullet can receive more force from pressure than a smaller bullet; all else being equal, it speeds up faster, and drops chamber pressures more quickly (all else is rarely equal though, since lead is heavy)
Now, the reason
rifle rounds universally blow handgun cartridges away is due to a single commonality; velocity. That's the key. Get that pill --any pill-- north of 2000fps, and you start getting an exponential increase in tissue damage
beyond the diameter of the round, basically because the force of the bullet pushing stuff out of its way is so powerful that cellular bonds tear. The target basically "splashes" upon impact.
Faster is better, but the trick is how to get there. Do it with a tiny bullet, and you have to make the thing very dense or hard for it to get deep enough before running out of steam or breaking apart, and that lands you in jail for making 'armor piercing bullets.' If you go much larger than 'tiny,' you will find your cartridges have to be really short & stubby to still fit in a gripped magazine well suitable for ordinary mortals, and won't have room for enough powder to push the pill down the giant bore. This can be mitigated a good deal with bottle-neck cases, which shift the equation to the opposite extreme, where you have more powder than needed to drive the bullet, and huge flash is the result.
Things that will likely be common for any high-velocity round;
-Sophisticated bullet design (multi-core, compromised tip/jacket, unstable)
-High pressure loadings
Those two things basically force the designer into a solution very much like the 5.7x28. Very high quality (expensive) ammo, and very clever (expensive) firearm actions. I think the one thing FNH could/should have done was to either tell NATO to shove their high capacity requirement and go with a 9mm case-head based round (like Tokarev, 30 Luger, or 22TCM), or split the difference and use a 32acp/30 Carbine case head. Stronger brass would be able to handle the high pressures with less wear, and the bolts/actions required would have more commonality & applicability to existing cartridges.
I think for defense applications you'd need to try to define and set your variables as a starting point;
-Velocity (I think 2500fps would be an excellent target; +3k is impossible at present for a handgun length barrel, at any pressure)
-Penetration Depth (mostly a function of bullet weight, speed being a constant)
-Barrier Effectiveness (likely limited by legal bullet construction)
-Max Allowable Recoil (a function of handgun & bullet weights)
-Max Effective Range (speed alone guarantees +100yd effectiveness)
-Max Handgun Weight (set by many variables after handgun size)
-Max Handgun Size (sets OAL of cartridge and barrel length)
-Min Ammo Capacity (very crudely sets the case head diameter)
-Bullet Weight (mostly a function of bullet diameter, unless odd shape specified)
-Bullet Diameter (set by barrel length & powder charge)
What I
suspect we will find, is that FNH engineers were pretty close to the sweet spot, but that more compatible components than the 5.7x28 uses wouldn't have changed the results much (well, other than allowing competitors to produce ammo more easily
)
-A large size handgun allows you to lengthen the bore for a larger powder charge
-High capacity forces you to use a small diameter case head
-High velocity requires high pressures and light bullets
-Large powder charge requires necked cases to keep length down
-Light weight is achieved by small ammo and action parts
I've heard it would cause problems for function, but if FNH made a "G26'ed" version of the five-seven with a cropped magwell (12-15rnds instead of 20) with less 'dead space' around the magazine well and even a marginally shortened barrel, they'd have a very competitive gun on their hands, simply because it would weigh so little and be the same size as other options. If they could make an even smaller single stack snubby that still functioned properly and got halfway decent ballistic figures, they could catapult the round to prominence and put a stake in the 380/32 mouse gun market.
TCB
