I would never choose a low power 5.7mm projectile over a 9mm or 10mm projectile with vastly more mass/momentum.
Low power?
9mm Federal HST 124gr 1150fps - 364 ft-lbs
5.7x28mm EA S4M 28gr 2600fps - 405 ft-lbs
Now 10mm is a whole other ballgame. BUT... are we talking about full power 10mm? Or are we talking about the watered down stuff that we mostly see available?
10mm Fed Hydra-Shok 180gr 1030fps -424 ft-lbs
This 10mm round is very close in KE to what I carry in my FiveseveN
Now, there are a few small manufacturers that load the real 10mm stuff and get 700+ ft-lbs of KE out of a 180-200gr round. That is some serious power and not only blows away the 5.7, but also all the rest of the semi-auto field. Those loadings are way too much power and penetration for use against humans and are primarily used for bear protection while hiking.
I own a 10mm but don't use it as my carry weapon. It is sooooo heavy compared to the 5.7, doesn't carry as many rounds, has too much recoil with full-power loads to aim properly in a self-defense situation, and offers too much liability regarding over-penetration in the case of a shooting.
It just makes no sence to me, especialy since the armor piercing ammo is no longer available.
Which armor piercing round do you want? The factory SS190?
Here you go:
http://www.gunbroker.com/Auction/ViewItem.aspx?Item=250146714
How about after market penetrating ammo at a much better price? Try Elite Ammunition.
Think about it, even with the same powder charge smaller caliber/lighter projectiles carry less wounding potnetial.
5.7mm has bullet behavior similar to a rifle. It is apples and oranges when comparing to common calibers like 9mm, .40, and .45.
5.7x28mm tumbles minimizing over-penetration and dumping all its energy in the target. 5.7 also creates massive wound channels (4+ inches) - something that 9mms, .40s, and .45s find hard to duplicate even with great expanding rounds like Federal HST.
The scientific studies as well as real shootings have shown that the 5.7x28mm has great wounding potential.
While caliber/mass is not everything it certainly has it's advantages, especaly when the KE is higher too, like the 9mm or 40S&W.
9mm, .40, and .45 caliber rounds do not have more energy than what I carry in my FiveseveN.
Now if we were comparing the 5.56x45 to standard handgun calibers that is a no brainer, having nearly 4 times the KE more then makes up for the smaller caliber and less mass.
And why do you think the 5.56 round has more power than the handgun calibers? It is going faster. That is what is happening with the 5.7. The round I carry in my FiveseveN goes over 3x faster than a .45 caliber round. That is how I can have more energy at 28grains vs 230grains. Add in the tumbling bullet behavior and now you have large wound channels out of a small bullet. It's very simple once you take a moment to think about it.
Small and fast = light weight, low recoil, high capacity, flat trajectory, and tight bullet groups. A high-tech solution for the soldier of the future.
And things will continue to get lighter and faster until we are shooting laser guns like Star Wars I presume.