I ordered few thicknesses of cork in sheets and I plan to cut some tight fitting wads from it. Although a card wad works great in a smooth bore I thought cork will have more purchase on walls of a rifled barrel so I'll try it first. I'm surprised there isn't a lot of people who resolved this problem already. Judging by the number of posts on different forums muzzleloading double rifles (even those with fast-twist made for slugs barrels) are quite popular.

My gun is a Pedersoli Kodiak Express Mk6 for which I have two sets of barrels, a short 24 inch .58 cal (1:48 twist) and a longer 28 inch .50 cal(1:24 twist). In .58 the powder charge is 120 grains, in .50 100 grains. I found .58 really likes moderately tight REALs and .50 likes maxi balls. With both calibres and projectiles the bullet is engraved by the rifling, but once initially engraved at the muzzle I can push the bullet the rest of the way with a slight push of one finger on the ramrod.

I tend to load both barrels, shoot both and then load both again rather than reload the fired barrel repeatedly. Currently I'm checking if the second bullet moved before firing the second barrel. The bullet almost never moves. I think I had it move twice in .58 and once in .50. I probably shot close to 30 times each side of each barrel with those bullets on the shooting range. I haven't done any walking with the rifle loaded. However, although the bullets almost never move I haven't got enough confidence in them not moving to for example load the gun, spend half a day walking with it. Shoot one barrel and then the next. I'm looking for some solution that will ensure they never move at all.

I tried wrapping an undersized minie bullet in paper when I was testing all kinds of projectiles to discover what the gun likes the most. Unfortunately it doesn't shoot minie style bullets accurately wrapped or not, but judging by the resistance felt when loading it would definitely work to stop the movement. If the wads cause bad accuracy I'll be trying paper wrapped maxis or maybe a a 50 cal government bullet next.