I would probably build a 50 cal hawkins:

http://www.midwayusa.com/Product/346...l-in-the-white

Here is a link with several other selection choices:

http://possibleshop.com/rifle-kit.html

Either 1:48 or 1:28 would do OK, you can use the big lead conicals (like no excuses, maxiballs, great plains hunt, etc) or I have good luck with Hornady 350 gr FPBs. I have killed two elk with them.