I don't understand what exactly you propose. Care to elaborate?
WTF is that?
These ideas range from "possible" to "possible but silly" 
What the hell would these do?
1. More ammo diversity for guns.
For example, handgun bullets usually come in Jacketed Hollow Point (JHP) and Armor Piercing (AP).
JHP bullets don't have pointy or ball shaped points, but rather a hollow point. These are often called "Dum-Dum" bullets. These bullets are meant to break and expand upon entering a body, delivering extra damage.
AP is there to pierce armor, like kevlar. They are crafted to penetrate through obstacles and keep going through.
JHP and other similar ammo is generally used by police forces and found in handguns and SMGs, and in some hunting rifles. They are good against unarmored targets, but they can't penetrate body armor or other obstacles - which is often good for police, because it also means they won't go through walls and hit civvies.
AP is generally seen in armed forces, operators, etc. They go through obstacles, but they can also overpenetrate and just keep, which means they won't impart all energy into the target.
Military Rifle JHP bullets do exist, but because the Geneva Convention prohibits expanding and exploding bullets in war, few militaries stock them. Only a few small factories make that. Besides, military rifles use FMJ bullets and these, at rifle speeds are often strong enough to make JHP unecessary. Besides, JHP would make them lose range and accuracy at longer distances.
(Rifles have JSP instead, not sure how good they are)
There's also +P rounds, as in More Pressure. Every gun can take X pressure before bad things happen to it. But sometimes, the gun can take more pressure than the round makes. Or maybe you brought a stronger gun made for +p ammo. So you buy or make a +P round and fire a stronger bullet of the same round.
There's also ball ammo, but I'm not sure how to rate it.
There's also weirder stuff. Did you know 7,62 x 51 NATO DUDS were made and tested? Depleted Uranium Sabots for 7,62 guns. Aparently, those were great armor piercers.
2. Wildcatting. Ok, so some people load bullets by themselves for reasons, like saving up money. That's called Handload. Some people make their own special, different loads, in small quantities. That's what we call a "Wildcat Round". For example, you could take a shotgun shell, and replace the shot with fewer, bigger balls.
3. Well, those were examples. Soviets made poison gas bullets, for example.
(honestly I just wish we got more cool stuff from autopsies and live captures. I had an idea involving spiders myself)
4. Flechettes. You know, not sure. AFAIK the main advantage of flechettes is that you can carry more rounds, and they are pretty good at penetrating armor.
Honestly, someone very good at this could inform you better than me. Where's the gunloving /k folks?
