I've been thinking about a 40 cal wildcat based on a 303 Brit or 30-40 Krag brass. Specifically for a lever gun.
Is anyone out there already making a long 40 cal lever gun?

The Winchester 1895 is available in .405 Winchester chambering. I don't believe they're making them anymore, but they were up until a couple years ago. A new one just sold on Gunbroker auction for $900, here is the link if you're interested: http://www.gunbroker.com/Auction/ViewItem.asp?Item=137470977

Don't know anyone making lever rifles for them but .40-50 Sharps Straight and .40-60 Maynard can easily be formed from .303 or .30-40 brass. My SPG Lubricants BP Reloading Primer says that Steve Garbe won the 1990 Nat'l Championship BP Cart. Rifle Silhouette Match with the .40-60 Maynard in a rebarreled Winchester High Wall. Also, no special case-forming dies are required. Just run them into the .40-70 Sharps Straight dies (or .40-50).

Interesting!

IMHO if you must have .40 cal, a 38-40 or .41 mag lever and ammo would be much easier to find. Cartridges Of The World lists several obsolete .40 cal cartridges for lever action rifles.

Keep yer eyes open for the 405 WCF. They come available from time to time. Very capable cartridge. I have a Ruger #1 chambered for that round. Love it, but it's a 41 cal, not 40. Uses the 41 mag pistol bullets for grouse and rabbits. Fun!

Davidsons Gun Gallery has just sent out catalogs of a run of several new Miroku made lever guns and single shots and several of the single shots are chambered in .405 Winchester.

I have two 1895 .405 WCF and one 1886 .45-90 rifle made for Davidsons by Miroku and they are excellent rifles. If you shop arounnd you can likely locate one. If you specifically want a Miroku 1895 .405, I can put you in touch with a person in Dallas that will part with his like NIB in .405.

There was a fellow some years ago who designed the 400 Yukon (.411" bullet) on the 450 Marlin case. There is also the 416 Barnes on the 45-70 but its got a .05" bigger bullet. A simple rebarrel of the Marlin 1895.

The 416 barnes was always a thought here but I have a 450 alaskan built on a 71 and a 416 alaskan (based on the 348) built on a ruger #1. I use the #1 to fireform brass and then neck it up to 45 works great.