I load 21.5 grains CSB5 with 24grams lead, Spark wad, CX2000 primer in Cheddite 69mm case, makes nice clay cartridge. I used same load with AS and its only slightly slower but negligibly so. Both loads have been pressure tested and CIP comply. I used A1 for 20bore loads and AS (now CSB5) for 12bore.
Lowest load for a 12bore is 28grams lead with Cheddite 70mm case, CX2000 primer, 27grains A1 power, 3mm overpowder wad, 21mm fibre wad, 3mm felt wad and 6 point crimp which gives pressure at 1" of 464,80 and velocity at 2,5m of 351 fps.
A1 seems to be for higher loads in 12 going to 40grams of lead.
Never used the A1 12 bore loads just what was on the data sheet. They all say 70mm tubes but whenever i buy them there all 69mm.