To the OP; you will need to change powders for really low pressure 20 ga. loads. Probably the best single powder for that purpose is IMR 800X. If you go to Hodgdon's website [they either own IMR or are the sloe distributors now], you will see virtually every 20ga. recipe w/800X meets the 'low pressure' criteria for 7/8 oz. loads using it.
I would recommend you stay with the 7/8oz. shot weight and if you want more 'thump' to use a larger sized shot/pellet. Also if you do a lot of surfing/reading on that powder you will find some remarks about it not metering well, in some loaders. Most all that kind of remark fails to make any mention of that last qualifier and had to do with some progressive loaders & how they were set up rather than there being anything specifically wrong w/the powder. There isn't. I have loaded quite a bit of it over the years using a single stage MEC and NEVER have had any issue doing so. I mention that only because I would not wish to see you discouraged when it will do exactly what you are wishing to do, perhaps better than any other powder presently available.
kind regards, tw
Last edited by tw; 03/18/16 09:25 PM. Reason: spellin'
