I have a problem with my presets.

I downloaded the BF3 clones and enveloped the simple ep3 trooper. Next i saved the presets and imported the other clones to my scene. I merged the body into one and the addon parts in an other mesh. Next i enveloped them and loaded the presets from the trooper for the body mesh.

But as you can see it is not very accurate: whereas the lower body works pretty good, the arms and hands are Diet Dr. Pepper enveloped.

When i first enveloped the addon parts - klick the addon mesh>add envelope>select only a few bones (ripcage, head, pelvis) - and after that enveloped the body - klick the body>add envelope>select all bones - the model becomes this after i loaded the presets:
Can someone explain me, why the presets are not that accurate??

Since those troopers are nearly identical you should have no problem using GATOR to transfer the weighting from the first one to the others with only minor tweaks.

Ok i'll try it. But why does the presets not work

I can't tell you without looking at your scene, maybe the difference in point order caused it, don't know.
The trooper in your top image in the first post still has transforms that need to be frozen and you need to give all these guys a kung fu grip so they can hold their weapons and drive vehicles correctly.