My instincts tell me to go with Maxi on this one. At least my own somewhat limited experience with gasket material tells me it ain't much good for our use in muzzleloading.
On the other hand, you personally may have better luck than I did, so give it a try.
A few years back someone mentioned it was the best thing since sliced bread, and MUCH better than whatever was in first place before sliced bread came along.
I tried it. I'm sure I tried better than 200+ shots. I tried it in 1/8" using 1, and sometimes 2 wads to try to make it work. I tried to lube it, and I tried to use it under a PRB, I even tried it with lubed Lee REAL bullets seated on it. I could not get anything to work. The fouling was a mess in every thing I tried. That cork seemed to multiply the fouling!
Now, having said that, I must say I have talked to people who say it's great. So maybe I did something wrong. Perhaps there are different "types" of cork, I dunno. I used gasket material from NAPA that comes in the 2 ft. square sheets and is 1/8" thick.
Maybe the cork from a bulletin board is different. Or maybe there is something in gasket material that is not in other types of cork. I dunno.
I do know all my experiments with it never panned out. There was quite a discussion on the BPCR board a few years back that dealt with this. I don't recall a lot about it other than some insisting it works, and still others insisting it didn't.
Wads from a plain old milk carton, print side down, makes the best wads I've personally ever used. That goes for BPCR, and Muzzleloaders. Of course one should never use a wad with a HB conical.
Respectfully, Russ