You might ask the other club members what they're using, unless they all use factory rounds.
I have to point out that I have never loaded a single shot shell in my life. Except for the part about exactly matching ALL components being VERY important for safety's sake, I know almost nothing about the intricacies. Please bear this in mind, if my subsequent ramblings make no sense or contradict established convention with shot shell reloading.
As the round is fired, expanding gas sends the shot and wad down the slightly constricting barrel, to the (choked or unchoked) muzzle. To accommodate the constriction, the shot must compress/deform/give in the process of traveling to the muzzle. A load of 1 & 1/8 oz of #7 or #8 shot consists of little spheres that will pretty readily compress/deform/give, to travel to the outside world. The individual pellets for those sizes run on the order of 0.088" in diameter. The diameter of #4 Buck is 0.24", almost 3 times the diameter of the bird shot. The larger shot tends to resist compression/distortion far more than the bird shot, which may make it prone to lodging somewhere in the length of the barrel, jacking up chamber/pressures to well over that they are stressed for, and possibly causing a catastrophic failure (a "Ka-boom" as it's sometimes called).
If your propellant is an Alliant product, you might examine their online shot shell loading guide. It seems they catalog data by charge weight, without regard to shot size (maybe it does NOT make a difference). Usually, there are two charge weights per load, sometimes 3. I wonder if you might be safe to use charge weights for 1 & 1/8 oz. loads, but make your "payload" closer to 1 oz. (20 or 21 pellets), then test it for patterning (and "Ka-booms"). You could increase charge weight OR "payload" incrementally, to see how it works.
I have to point out that I have never loaded a single shot shell in my life. Except for the part about exactly matching ALL components being VERY important for safety's sake, I know almost nothing about the intricacies. Please bear this in mind, if my subsequent ramblings make no sense or contradict established convention with shot shell reloading.
As the round is fired, expanding gas sends the shot and wad down the slightly constricting barrel, to the (choked or unchoked) muzzle. To accommodate the constriction, the shot must compress/deform/give in the process of traveling to the muzzle. A load of 1 & 1/8 oz of #7 or #8 shot consists of little spheres that will pretty readily compress/deform/give, to travel to the outside world. The individual pellets for those sizes run on the order of 0.088" in diameter. The diameter of #4 Buck is 0.24", almost 3 times the diameter of the bird shot. The larger shot tends to resist compression/distortion far more than the bird shot, which may make it prone to lodging somewhere in the length of the barrel, jacking up chamber/pressures to well over that they are stressed for, and possibly causing a catastrophic failure (a "Ka-boom" as it's sometimes called).
If your propellant is an Alliant product, you might examine their online shot shell loading guide. It seems they catalog data by charge weight, without regard to shot size (maybe it does NOT make a difference). Usually, there are two charge weights per load, sometimes 3. I wonder if you might be safe to use charge weights for 1 & 1/8 oz. loads, but make your "payload" closer to 1 oz. (20 or 21 pellets), then test it for patterning (and "Ka-booms"). You could increase charge weight OR "payload" incrementally, to see how it works.
