I picked up a Borchardt in this caliber. Its set up as an offhand rifle with palm rest. The curiosity is that it has a gain twist. I always thought this caliber was a jacketed bullet cartridge. Could this be a lead bullet only rifle? Can I use jacketed bullets in a gain twist rifle? I need help with this one.
  Don

I can't help much. but I do have a Shiloh in 30/40 and it loves cast. I shoot a Lyman 311284 at 210 grains and it will smoke bowling pins and my chicken swinger at 300 yards all day long. Mine is a perfect 10 twist bore.

30/40 can be a very good cast bullet case. I used to shoot the 200 gr Saeco gas check at 1600 fps in CBA postal matches, won a few too. 

If I had a good Borchart set up for offhand would try it and see before changing.  If match rules don't allow gas checks run it slower and leave the check off, same bullet. Plain base a 32/40 is probably going to out shoot it, offhand doubt if there is enough difference to notice

Boats

30/40 for offhand depends on the match and rules.  Case is almost the same capacity as 308 and very suitable for silhouette if using a single shot

Schuetzen with plain base another thing but way I count from ASSRA Journal about a dozen active offhand shooters in the ASSRA. Build it for Silhouette with jacketed leave the gas check off to shoot Schuetzen put the checks on for CBA 30/40 is a good choice 

Boats

CBA is cast bullet assocation and they have single shot classes. CBA runs a very good postal match program .

Unfortunately if offhand is your game it's postal or NRA silhouette. Best offhand shooters are now shooting Lever Silhouette.  20 plus years ago setting up my CPA Schuetzen number of good shooters on the East Coast shooting Schuetzen offhand. Now the only real offhand competition is Gallery at Conestoga. It's a good match with top level competition though.

I have thought about making a long trip west to attend offhand matches with my Schuetzen and Lever guns. Be a fun trip. 

Boats