A question for those of you doing such:  I recently started out experimneting with breechseating in my 32-20 BPTR - a BSA Martini with  .308 1 in 12 barrel.
I am using a plugged case for breechseating, but I amm running into an issue when shooting this way:
A fouling ring is forming in front of the case, and 2 moist patches aren't getting it out - it really needs some serious brushing.  Now the rifle being a MArtini, this is not really easy to do, of course...
Any experience, solutions for this?  How are you dealing with it?  Being a 30-20, the amount of powder is pretty small, but still...
When I am shoting fixed, no issues with this crud ring, BTW.

My rifle has the hole, but taking out the action after each shot isn't really an option, unfortunately - I have 30 minutes for 13 shots.

     I have been experimenting with wiping patches cut from micro-fiber dust cloths.   The stuff has quite a bit of scrubbing power, compared to flannel patches.   I wet them and squeeze dry in my hands.   This seems to hold enough water to do the job.
     These patches are. rather thick, so you will want to have/make a special jag to give the bore contact you want.    
     In the big ML rifle, I either dry the bore subsequently with paper patches cut from a roll of paper shop towels, or wet with 20% glycol in water.   This will leave the bore either wet or dry, between which there is a difference in the velocity.   At shorter ranges, you will not be worried about  minor velocity differences.  Using only water, the bbl can sometimes be either wet or dry, depending on temp and humidity.  Adding a little glycol (antifreeze) causes it always to remain a little wet.

CHRIS
RGChristensen

I wonder if a German stop ring bullet would solve the fouling problem but then it would no longer be breech seated rather a fixed cartridge. When shooting black powder and with the right alloy and obturation does one gain anything by breech seating?

gert,
as usual you come up with an interesting problem, and in this case not a pleasant one.
not having an answer, some things that come to mind.
would it be worth comparing 1f, 2f, and 3f powders of best quality?
would it be worth trying a kicker of 4f, as in duplex, but with all black?
faster powder in the small case might work better, but might also make the problem worse.
could a felt wad soaked in grease replace the overpowder wad with a wax paper under it for any benefit?
if you are running an airgap, could some wad fill that space to prevent the issue?
i have tried a 1/8" felt wad in the airgap of 40 and 45 cal breech seated loads, and it works well, both greased and ungreased, but your round will probably have a smaller airgap.
straight felt will compress a little, while greased felt will not.
keep safe,
bruce.

Gert, 
Above is a PIC of wiping/cleaning my 12/15 from the breech.
I make up wiping rods in several sizes of delrin/acetal 
The above is 3/16" to fit 22 cal and up.
stock. Have made them up in larger sizes, mostly 5/16/with a rod guide to wipe TDs and Martini's

The wiping is not the problem, I have the flexible rod. But the crud ring is pretty tough, too much for a simple patch or 2 when breechseating.  A brush might work, but even then....  No such issues with fixed ammo.
Still, I would like to see if breechseating can give better accuracy.

What powder are you using?  Could that be part of it maybe?   

I only ask because I have not experienced any crud ring build up with BP, but I have had a very hard carbon ring in my Ruger #1 in .32-40 when shooting SR-4759. 

Chris.