Hey cross,
The Germans used different 88mm guns on the Tiger I and Tiger II so, you will need to search out the dimensions on the net for either gun. The Tiger II used a much more powerful main gun that was made by a diff. company IIRC . There are pics of a Tiger I with 88mm rounds sitting on it, while on display during a Russian war time exhibit, that you could probably use for a rough idea. Also try "www.alanhamby.com/tiger.html" for lots of info on the Tiger I which, I assume, is the version that you are working with.