I wouldn't use the Kmr82 for ambience, as it is only mono. Also, keep in mind that it is pretty long. Long guns and Rycotes can sometimes be a bit much to lug around.
I've never used the 82 myself, but John Fasal has a 82 and I have seen him use it on gun recordings a lot. It sounded great to me.
I've never used the 415T either, but I would try to get a 416 p48 instead. That way you won't have to worry about using a T Power - Phantom power converter (assuming your mixers/recorders are all phantom and not T Power). Also, those old Sennheisers used Tuschel connectors instead of regular XLR connectors. Which means you'll need to buy yourself some connectors and build your own cables, instead of just grabbing an XLR off the shelf. Not a problem if you can soldier, but more added work.
I owned a Sennheiser 816T for a while, I sold it because it was too long to lug around, I had trouble fitting it and the rycote into any of my cases, and hated having to remember to use a T-Power converter. I also had to build my own cables because it had a Tuschel connector.
Unless you really need a long gun, a Sennheiser 416 or MKH60 or a Neumann KMR81 will be much more friendly to you.