Well, it's been a month and no replies so I will chime in. I don't think you will have very good luck doing what you suggest, too many variables to get consistent results. But it wouldn't hurt anything to try it, so give it a go and let us know what happens.
If you want extremely high velocity from your 8mm, you can try turning some aluminum bullets just under bore diameter and patching them up. That does work as long as they will just barely fall through without the patch.
Of course neither of these solutions are very useful past very short range, and it is way easier to get a .223 or some such and just shoot normal cast bullets in that! But where is the fun in doing something that you know is going to work before you start it...
