Creating separate components yet with a common surface without any inter-penetrations

Hello!

I'd like to create a bullet as shown in the image attached. It has a core and a jacket around it. They're touching but have no penetrations. I drew the geo in SolidWorks and imported. But when I use the general approach of partitioning and solid mapping, in my analysis it will show penetrations between the jacket and core. How do I go about avoiding this? 

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