I got a few CTS 40mm sting-ball cases to try and reload for my registered DD M203.  The seller advises that they use a 38 Colt Short blank.  I have 38 S&W blanks for reloading chalk practice rounds but am finding few sources for 38 Colt short that are not black powder for cowboy action events.  Has anyone ever used the 38 S&W in place of the 38 Colt Short for this purpose?  I know the cases are different by a few thousands of inches on all specs. but thought I would ask.  Grog  may know, as he is the 40mm go-to guy.

Don't use the 781 blanks in the short colt casings. They use very different powder. I recommend popping the short colt blank out, reloading the primer, then using 3-6 grains of Bullseye, a small brass disc punched from hobby stock .015" thick sheet brass. I bought a punch that knocks out a 3/8" disc that fits inside the aluminum casing tight. Load your brass with new primer, powder (3 grains for foam rubber bullet type, or 6-7 grains for 781 type solid projectiles for range) then replace the brass into the base of the casing. I use a press to squeeze the brass back into the aluminum base so it is flush. Hope this helps, GROG

Thanks grog, great info.  The trouble I was having was with getting the blanks out.  I think Godzilla was on the press that day.  When I try to knock them out with a punch that fits the hole in the case it just pushes out the primer and wrecks the back of the casing.  I ended up drill and threading the cases for 1/4-28 and use a spacer, bar and Allen head bolt to pull them out.  I will have to get some 38 Colt Short cases and try reloading them with your formulas.  Do you think crimped blanks would work?  They come in half and full load, smokeless and BP.

I have not tried crimped blanks with those. You can open the vent hole up enough to fit a larger punch, use a larger hammer (:)) and whack away. Opening the venthole won't hurt the effectiveness of the casing that much (1/4").
Also, I use 1/4" thick foam rubber (available at hobby stores) to cut 38 wads to keep the powder in the brass when you replace them in the 40mm casing. Replace the brass in the casing before you reprime the brass if you need to knock them in hard... That is the best way I have found to reload those casings. GROG

Cool, I was afraid that if I opened up the vent hole past the mfg. spec it would effect the performance of the case.  I am going to order a bunch of 38 Colt short cases, about 100, and start reloading some less-lethal for training.  It is hard to find a supplier of 40mm ammo that does not want the order on department letter head and the new chief didn't want his name on my personal supply of 40mm ammo...too bad the old one retired, he was a gun guy and would sign off on everything.  I should have stocked up when I had a chance LOL.