In going through W.W. Greener's book, I see loads for 20 bore used in trials, to be 7/8oz to 1oz. with 2 1/8th drams,
ie: 58gr.Bp. This was ctg. in 1868 trials, I think. charges ran up to 2 1/2 drams: 68gr.

You can take from this, any load of powder under 3 drams
will produce less pressure than given in Lyman's book & indeed they do. The lightest loads given by Lyman are 2 1/2 drams, ie: 68gr.2F GOEX used for all loads.

In Lyman's book using:
7/8oz. with 3 drams (82gr.)Rem plastic piston 5,780 LUP
7/8oz with cards and plastic PGS over powder 6,820 LUP

1oz. shot Rem wad 3 drams 6,040LUP
1oz. shot Alan PGS + 1/2" felt - 3 drams 6,920 LUP

1 1/8oz. Rem wad - 3 drams 6,980LUP
1 1/8oz. PGS + 1/2" felt 3 drams 6,920LUP