I believe a 12 gauge, 3 1/4 Dram EQ, 1 oz. shot is pushing close to 1,300 FPS. I shoot RST MaxiLite 2 1/2 inch shells in my old guns, 1 oz. load at 1125 FPS with a pressure of only 5,300. For over the counter shells, I will use Federal Grand Papers sometimes, 1 oz., 2 3/4 Dram EQ at 1180 FPS. But... with the amo shortage going on, finding any shells is not easy right now.
If your gun was made in 1903 it is not a Field Grade, it would be a No. 00 and this "00" grade designation should be stamped on the barrel flat and water table. The Field Grade came out in 1912. You could order a research letter from Jim Stubbendieck here to learn more about your "new" gun.
Don't let the seller do that, take it to a real gunsmith and have the crack properly repaired.
Hope that helps,