Re: NAM Gyro 500 (Update)
Well, I'm not exactly sure what you mean by that (Mach 3 projectile + body = not good, which should be obvious)... but I'm going to interpret that question as "Would the gyrobullet, if penetrating someone within the distance of a meter or closer and exploding, affect both the shooter and the victim?"
Depends. There are a lot of factors that have to be taken into account.
First off, it would depend on the material of the target (intended or not intended) and it's consistency.
If the wall the gyrobullet would be accidentally shot against were made of, say, wood, it would probably burst into the wood and shatter the wood when it explodes. The splinters and maybe a few shrapnel would blast in the direction of the u blah blah blah huge explanation.
I was going to explain this in detail, but I feel a summary works better. Basically, either two things can happen: the gyrobullet penetrates the material, or it doesn't. If it doesn't, then you have the problem of the gyrobullet exploding out in the open. If it does penetrate, then the gyrobullet will blow up within the material, and chances are little to none that there will be a problem.
The case with flesh is that the gyrobullet penetrates and explodes inside the target. The material is soft enough that the gyrobullet penetrates, but there is enough of the material present to sink the tip of the gyrobullet into the explosive chamber which then ignites the explosive charge. The gyrobullet would then explode within the target, but with the organs, muscles, bones and other cartilage being in the way of the shrapnel, the resulting blown-off pieces would just displace across the body and come to a stop.
And that brings us to our second factor: how thick the target is.
Obviously shooting a forearm or shin would cause the target limb to be basically blown in half, but would the shrapnel affect the shooter if the victim is close enough? It's possible. The shrapnel could well blow out of the victim and cause some damage to the shooter. Thigh or a shoulder? Depends on thickness, but usually it's thick enough to stop outgoing shrapnel.
However, if you shoot the torso, it's not gonna happen, as the torso is much thicker and deeper. The head might have differing results depending where it's shot, but chances are not as likely once more due to the bone structure stopping outgoing shrapnel from coming out.
Finally, the third and last prominent factor that should be taken into account is round type.
A standard gyrobullet round would not be able to penetrate into most walls before it explodes. An armor piercing gyrobullet, however, would, because it's tip is made sharper and more durable, thus allowing it to penetrate into a target before exploding regardless of what material it is (well, excluding some really strong materials and metal alloys and all that, but common materials would be most likely penetrated and whatnot).
There are other factors, such as how the gyrobullet hit (if it grazed, it's obviously not going to explode, as the tip didn't even touch the target), where/what the gyrobullet hit (if it shot a hole into an ear or tore a finger in half, the tip charge won't be triggered as it is not sufficient material to push the tip down and cause an explosion, whereas shooting through a hand might cause the gyrobullet blow in mid-air), etc...
The gyrobullet is not something taken lightly. And again, the weapon was designed with Freespacer Automata in mind. For automata the bullet shrapnel wouldn't be a problem at all, since they're made of metal and all. To any fleshy being, however, it might pose a potential threat.
It should be noted, though, that the fragments are pretty small, and chances are not a lot of them are going come out if they just burst from inside a body part. If you're wearing thick clothing or some amount of armor, you're basically safe from any collateral.
I think a lot of the outcomes of the use of the gyrobullet should be determined by judgment factor from the GMs and the players but the above are the standard guidelines of how it'd work.