The 20ga cartridge has higher pressure than 12ga or 16ga. Might try to stick with original 20ga load which was 3/4oz now available as trainer or low recoil. Fiocchi at about 1050fps is just one example. Specialty ammo companies like RST probably offer more loads like that. PolyWad even offers affordable GreenLite steel loads in 20ga for situations where non-tox shot is required.