Dave
That's a fantastic looking model---what a beast! Love the paint job, and it's very well executed too.
One thing you might want to know---it's been a hot debate in the modeler./historian world about what color was used for priming gun barrels,and I think it's pretty much been determined that barrels were primed in a dark charcoal gray instead of the red primer used around the rest of the tank. Just something to consider if you want to enter this fine model into a contest anywhere--the judges might "ding" you on accuracy on the barrel. In any case, it would be a simple fix--just a bit of black mixed into Panzer Gray would do it and then run the barrel very lightly with some graphite powder to complete the look ;)