I shot a lot of BP in mine, over a 6 year period when it was a 45/70 and had no problems.

You can also clean them by firing a number of smokeless rounds through the barrel but, you still need to wipe the muzzle off with a water based cleaner.

Frank

I would think that if your using full charges for whatever cartridge your Borchardt is chambered for then the cartridge case expanding on firing will seal the breech. You don't have to avoid water based solvents, you could make up a 'boiling out funnel' as used by the British during the Victorian era. Kynamco here in England still make them in a couple of large calibres, but none as far as I am aware for US calibres. However having shot a number of BP rifles chambered for the large British rounds eventually some fouling will get back onto or into the breechblock and action and failure to clean this out will cause corrosion and stiffness in the trigger action over time.

It only takes a few minutes to clean any black powder rifle and I always used boiling water with a little liquid soap added. Have a look at the Kynamco website and look for the funnels under accessories, you should be able to make one up for yourself without too much difficulty.

See:- (You need to Login or Register to view media files and links)

The funnels are shown in the left hand column some way down. Not cheap but you could make one out of a cartridge case with a little ingenuity.

Harry.

Brake and carb cleaner probably should be kept off the off the wood.  they have some pretty potent solvents in them.

I have used a spray action cleaner  I think it's a Rem-clean product with fair success  it rinses an amazing amount of junk out of my martini actioned German and Swiss schuetsens after a day of matches. 
I use the "straw" and keep it off the wood. before using it I give the stock around the action a wipe with an oily patch and promptly wipe the oil and any accidental overspray off right after "flushing" the action onto a couple paper towels.

Very seldom clean my actions. They seldom need cleaning. Dumped a bunch of BP in my new Sharps 74 last week. Should probably clean it................naw. Looks like it all came out. 



    Joe.

Balistol from Buffalo arms is good for cleaning wood and black powder fouling. Real snake oil stuff. Stinks but works good. Been on the market since the late 1800's.
Don

Urine is a great solvent but it is hard to control the chemical balance.
 
SS

Asparagus...