I just acquired a used single shot rifle that was supposed to be in .40 Crossno but isn't. 
It is .40 cal. but the cases that came with it are 9.3X74R.  Only one was expanded to .40 all the rest were still 9.3MM.  I'm guessing the seller never fired it.
Is anyone familiar with a "wildcat" .40 cal. based on the 9.3X74R cartridge?
The chamber is cut to accept the full length (2.90") of the metric case.  The chamber will not accept a 40-65 case.
Seems like it would have "ample" powder capacity!
And, I know, I know, a chamber cast would help; I'll need to get some casting material.
Any thoughts would be appreciated.
Mike.

Full length should be more like 40-85/40-90 Ballard. That's what you could call it if you wanted to shoot it in a match;-)

I'm with oneatatime,  9.3x74 is a drop-in for .40-85 Ballard. Rim is a little small on the OD but they work.

I use 9.3x74R to make my .40-85 Ballard cases. Just expand to .40 caliber, and then fire them and they finish forming out. Prior to firing they're slightly wasp waisted. But they shoot as accurate while finish forming as they do after formed.
No trimming required either, as the length is perfect.
.40-85 formed from 9.3x74R is the top cartridge:

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I believe Dave's .40 Crossno was a .40-82 using a .45-90 case to form them.

700-X shotgun powder burns like Bullseye so it should be fine with COW. Maybe start with 8 or 9 grains and work up until you get a good form. The wad is just there to keep the COW from falling out so maybe 1/8 floral foam or I've used some old bullet lube flattened to 1/16 between two sheets of Saran Wrap with a rolling pin and just pressed over the neck. Vall should have good ideas on this.

Marlinguy,
What shell holder do you use?  Seems to be little info on the 40-85 cartridge.
Mike.

I have a Hepburn in .40-90-3-1/4”.  It came with Norma 9.3x72R cases, which I’ve supplemented with RWS cases and Bertram .40-90 cases.

The loading dies that came with it had a .44-40 shell holder and a note that this works with the metric cases.  It also seems to work with the “real” cases.

I give the 9.3 cases a light anneal, use ~10 gr Unique and the rest of the shell full of COW and fire form.  They straighten out good enough to load .40 bullets, although they’re short.  They never form all the way down to the base, but they at least work.  This is an original chamber, of course; not a Shiloh Sharps or other custom chamber based on .405 or other basic cases.

I have recently begun fire forming 9.3X74 cases to fire in my 40-90 Ballard.  A couple of things I've discovered include; I can use the same shell holders listed for 44-40 WCF with my cases and they work perfectly; I prime a new case, add 60 gr +/- of 2f GOEX black powder, top the case up with cream of wheat then "cork" the case with a wad of facial tissue; after the first firing, the cases are a little "wasp waisted" but I load them with by filling them early to the mouth with the same GOEX and top with a 40 cal bullet that now will fit the case mouth; finishing the round with moderate compression.  After firing this round, the case is a perfect fit in my chamber.

I'm sure there are better ways to do this, but the process I've described works for me.

Froggie