I tried the 300 grain .54 caliber REAL in the 1:60 twist of my .54 Great Plains flintlock. A 95 grain load of GOEX FFFg with a wonder wad under the bullet gave me six-inch groups at 50 yards. A 70 grain load gave me five-inch groups.

I have to note however, these were bullets I bought on-line and I found them very inconsistent as to diameter. On some, the rifling barely cut the top band. On others it fully cut the top band and partially cut the second band.