Corn meal absorbs moisture from the air easily , and your cases will swell if you use it as a shot buffer, unless you take the added step of sealing the casings with wax. In a ML, where you load the powder, wads, and shot as needed, it would take some considerable time to get the corn meal to filter down through the shot so that it is consistent. There are lighter, synthetic materials like " Puf Lon " that you can buy to do this, that don't absorb moisture, and will not swell, but are so small that they easily filter down between your shot pellets. The only problem using " Puf Lon " ist that the stuff is so light its blows away in the wind, so you want to premeasure the amount of puflon needed for each load, and carry it in a separate tube. Then all you have to do is dump the stuff down the barrel, and run your OS card down on top of it. The air being pushed ahead of the OS card should push the Puflon down in and throughout the pellets, displacing the air that exists between the pellets. If you carry Corn Meal in a metal flask with a good valve closer, it should not take on moisture readily in the field, and you might be able to use it effectively. Don't use the coarse ground corn meal like you get from mills. Buy the corn meal that is sold in the grocery store in mixes, because it is much more finely ground, more like flour. The finer the meal, the better job it will do cushioning the shot pellets.
Personally, I think you will get better patterns using plated shot, and some kind of shot cup. If you keep your velocity down under the speed of sound, and use FFg powder instead of FFFg powder, you should not get pellet distortion in the barrel from firing the load, as the slower burning powder with a light charge will push the pellets without distorting the back (or bottom) row of pellets. Conversely, using heavy loads of faster burning powder slams that back row of pellets and causes them to go out-of-round.By using a shot cup, you protect the sides of the outer pellets from being flattened by rubbing against the barrel as the shot column exits the barrel. That has always been the main cause for patterns losing pellets on the fringes, and how the term " Core Pattern " came to be used to describe the middle part of a shot column that will not be distorted or flattened so that the pellets can continue to fly true. In effect, until the advent of modern plastic shot cups, and plated shot, we were sacrificing (wasting) the outer layers of pellets that we knew were going to have flats rubbed on them, which causes them to quickly slow and fall out of the core pattern. To compensate for this loss, we had to use larger gauge shotguns to get the same amount of shot in a pattern at longer range.
With the modern plastic shotcup, and plated shot, small gauge guns have been able to deliver much higher percentages of their pellets on target at longer ranges. Buffers seem to help the really large shot, Like #3, #2,#1,BB,and T shot. In " non-toxic " pellets, the buffering does not seem to do much good except with Bismuth, which tends to be brittle, and shatters on firing. I am not current on testing done using Bismuth and BP loads, but obviously the gentler shove of BP would iad in keep the Bismuth pellets together. The real problem to date has been that steel shot is so light, it doesn't retain much energy at waterfowl ranges. Some of the newer Non-toxic shot offer promises of better patterns( hevi-shot), or even being able to use them in standard shotgun barrels with standard chokes. We shall all see. To date, only a few of the newer shot manufacturers have offered the shot as a component, so that reloaders can do their own experiments. Unless its sold as a component, its not available to us BP shooters.
