Short update: After some measurements and thinking (and more measurements), Tom at Accurate Molds drew up two new designs, which have now been ordered. Due to delivery times and traveling, I will have to wait until January to try them out.
http://accuratemolds.com/bullet_deta...=43-350K-D.png
http://accuratemolds.com/bullet_deta...=43-400K-D.png
Thanks again for all your input,
cmk