I know that the 1 in 18 ' twist will limt the weight of the bullet I will be able to use.  I'm planning on using a 335 grain cast lead bullet.  I'm not sure if a 400 grain bullet would stabilize with this twist.   

 

After some consideration I have decided not to do the 40-65 Winchester.  Just not strange enough.  I think I'll make a .411 Nagant.  This is a 7.62x54R case with the neck expanded out to take a .410 caliber bullet.  I have been reading about a 430 JDJ and I think the .411 Nagant will be a little more.

 

The case will have a neck that is .500 long.  This will give it great support for cast bullets.  I will keep the body taper the same so the cartridge will have a very small shoulder but the length will be the same as the 430 JDJ but the body is bigger.  These combination should give me  round that will match or excess the 405 Winchester in a bolt action.  I know twhat you're thinking... why not just fit a 405 Win barrel to the action?  405 Win is just too long.  I will post some pictures of the case as soon as I can get it made.