D Norris, I don't know how you'd attach a GC to the base of a Lee REAL bullet. The better way is to get a 1/2” arch punch and cut overpowder wads from tablet backing or ~1/8" hard felt (Google Duro-Felt products if interested) and soak the latter in melted Crisco, drain and load over your powder charge followed by the REAL. Speaking of which, 100 grs. (FFg?) may be excessive IF your bbl. is 28” and it is loose rather than in pellet form. As for REAL's in a fast twist, I've never heard that one before, but the bigger issue may be how well they fit your bore. E.g., I had 2 new REAL .50cal. molds (~250 grs.? & ~350 grs.?) and found they were too small for my Knight Bighorn. Just for grins, I paper patched the heavier one and got an immediate improvement in accuracy. You may wish to try that trick as well. Lastly, the admonition never to use WW projectiles in ML's is practically an old wives' tale. I know several shooters who do so with no ill effects. Keep in mind, REAL's cast of WW's will be lighter and of slightly greater diameter than those cast of Pb. If your bore is on the large size and the REAL smallish, by all means try WW's. They cast more readily than Pb, btw, but I don't know how they perform on game.