I am not sure what he was trying to tell you. Traditionally, you load two balls ( at your own risk) down the barrel, both being PRB. He may have been trying to keep the shape of the second ball from being distorted by the first ball banging into it when the gun fires, by using a "filler", like Corn meal between the two PRBs.
I am not a fan of shooting double balls. Some say this is just the " medicine " for bears, and other critters who can bite back. I prefer to use a large bore gun, and not tax the gun barrel with the increased pressures you get using two balls on top of a load of powder. If you do try shooting such loads for accuracy, you will find that the balls can be loaded to hit fairly close to each other MOST OF THE TIME out to 50 yards. After than, they begin to fly their own ways. The one in back tends to be the more accurate out of both rifles and smoothbores.
I have never tried putting a filler between two balls. Remember that whatever the weight of the filler is added to the total weight of both balls, and that is going to increase recoil, and chamber pressures. Be sure you are using a good, new nipple on a percussion rifle you choose to shoot these kinds of load.
Personally, most shooter don't shoot enough to be able to handle that added recoil, and therefore can't hit close to where they are aiming. Killing game, particularly dangerous game, requires Accurate ball and bullet placement.
Most shooters are trying to compensate for poor shooting skills by shooting heavy powder charges, or, like your friend, shooting multiple projectiles, hoping something will hit. We see this with the Zip Gun shooters and their sabotted pistol bullets at the range all the time.
They wound a lot of game that they don't recover. That just proves that in addition to having very poor shooting skills, they have NO woodsmanship skills, either.
When I was younger, we called these guys, "slob hunters". I think that name is no longer appropriate for these guys as it insults slob hunters!
Last Thursday, my brother was at the club range testing one of his guns, and shooting open sights at targets at 50 and 100 yds. PHil was taking the x-ring out of his 100 yd target. Some guys with new zip guns, all with large scop sights mounted were blasting away near them, and they finally got curious about the traditional guns and underhammers Pete and Phil were shooting, and came down to look and talk. They had not gotten a round on the paper much less put one in the bullseye. But, they were " zeroing " their zip guns so they could drive to Illinois in time to hunt deer this past weekend. They were astounded at the small groups that both men were producing using open sights. When they left the range, they still had not hit their targets. They didn't know how to sight in the guns, or shoot from a bench rest, or how to find a load that shot well. One guy was using 150 grains of some substitute powder in his gun, and was flinching badly every time he pulled the trigger! You think? :youcrazy:
ff :shake: 
