Don
I would use a 40 stright case. Anywhere from 40-50 to 40-70 would do the trick. Using the stright case you can seat a wad anywhere along the inside length of the case. I would start with a 40-50 stright then if you want to cahnge anything there is room to re-chamber. 
40 Rod

Good morning Don!  When I started playing around with that .40-40 Maynard of mine (which I made from a .30-40 case with a brass "washer" added to the rim) a while back, that pathway showed a LOT of promise very quickly.  Since there are several standard .40s that are basically the .30-40 or .303 Brit case straightened out and cut to length, that is where I would go if I were pursuing the project you mention.  IIRC, the later "normal rimmed" Maynards in their .40 cal series were available in 40, 50, 60 and 70 grain loadings by simply making the chamber and brass longer.  This would be a pretty cool way to experiment as well...start small and go until you get the result you want.

All the best,
Charlie the Frog

Thanks Men;

Those are the kind of comments I hoped to see. And from those with experience with .40s. I am aware of one .40 using a short tapered case. This one is very interesting but is a breechseat-only proposition . It might be the ideal should I commit to such a project and restrict it to schuetzen only. I am not sure I would want to preclude the use of fixed ammunition. 

Glenn;
Re: your comments regarding rifle weight, I have thought of that . Weight may be the easiest part of the equatiion. There are downsides to the idea like heavier recoil and handling the heavier rifle required. The major possibility on the plus side might very well outweigh all the negatives. BTW, this would be a bench-only rifle as is 40 Rod's .40.

Ron Long shot a High Wall .40/65 for a bench gun at Golden one year (early '90s) - very accurate.

While working up a load in the 100 yd. tunnel it literally put 5 shots thru the same hole. I didn't believe it and I was watching!

Good shooting!

Bench only may be the saving factor with a 40 cal. You can make the rifle as heavy as you like

I shoot both 32/40 and 38/55 offhand.  I can tell you there is a definate fatigue factor in the larger cartridges shooting a Hudson match. I still like the 38/55 and shoot it often but if I was betting on scores would pick up the 32/40 evertime.

Boats

Gentlemen;

I will fill in some blanks which I purposely open in my initial post. Thise who know me know this already - that I am right-handed and WAS right-eye dominant but now shoot left handed and with all the magnification I can get. I manage to do relatively well off the bench though any good shooter need not fear. I do however require some spotting assistance at 200 yds and sometimes at 100 with the .22. What I intend to experiment with is how much better I might be able to see the bullet holes made by a larger caliber. That would make things much easier.
Over time I may play at offhand (and maybe with offset scope mounts which would allow me to shoot RH again) to see what sort of proficiency (?) I might attain. Given the high magnification scope required and the attendant eye fatigue and at this point, the extreme wobble factor from the LH thing it makes more sense to shoot BR and enjoy it. All that said, the heavier recoil and necessarily heavier rifle would be a small price to pay if it makes it easier to continue to enjoy the sport and need to trouble others less in order to do so. FIRST I need to see how much it might help things.

greetings don h,

have a 40 breech only. the case is a 30-40 krag cut off at the shoulder. shoots great..

,,ttfn..grampa..