If you are going to use a filler behind a load of shot, use some kind of wad- OP Wad, OS Card, Cushion Wad( altho enough filler will do the same thing that a cushion wad does) under the load of Shot. As long as the powder charge is down at the breech( a bump of the back of the barrel with the butt of your palm will shake loose any powder that is sticking to the sides of the barrel and settle the powder at the breech), you can just go ahead and pour the measured load of grits, or other filler, down the barrel.
I now am using an OS card under the shot( over the filler), and then another one- or two in my DBL shotgun- to seal the shot loads in the barrels. I put an off-center hole in the cards, using an awl, to let air escape to aid in loading the cards.
In a DBL shotgun, I use two OS cards, because the recoil of firing the first barrel can loosen the OS card in the second. Using two OS Cards has the same effect as using a lock washer on a screw to hold the nut in place.
The Second OS card is not necessary in a single barrel gun, unless the Cards are not a tight fit. If you have that problem, I recommend ordering the next size gauge wads( cards) and use them in your gun, instead.
Using Os cards, instead of heavier wads, reduces the weight of each such " wad"(card), so that your pattern is disrupted less. In cylinder bore guns, you need every bit of help you can get to fill those patterns. You don't need a heavy wad following the shot out the muzzle to bump the back of the shot column in the air, with the same effect as a cue ball hitting pool balls.
While that load of shot pellets is all together during the first 9 feet in front of the muzzle, it creates a vacuum into which the following wad(s) are sucked, or " Drafted" if you prefer the use of NASCAR terminology. The lighter the "Wad(card)", the less likely it is to be sucked into the back of the shot column, and the more likely it will quickly fall to the ground. The off-center hole in the card helps it fall away from following the load of shot, by making the card unstable, aerodynamically.
In actual firing, its not unusual for a 1/2" cushion wad to travel more than 20 yards from the muzzle. Most Os cards are found on the ground within 15 feet(5 yds.) of the muzzle, by comparison. :hmm: