The A400 here may choke on 3/4 oz loads. It took a while to make it reliable with 7/8 oz stuff, but now it eats them w/o a glitch.
I do load 3/4 oz in 12 gauge for new shooters. Oft these are for the little 12 gauge H&R single with the 12" LOP that I loan out to new, pixie sized shooters.
Here's the recipe, I think. I'm at work and can't look at my notes.
Remhull, Gun Club, STS or Nitro.
Win 209 primer.
16 gr Clays.
CB 1 oz wad, the clone to the WAA12SL.
3/4 oz of hard premium shot.
Zero wad pressure.
I don't have crimp problems with this and require no Cheerio or other filler for a good seal.
Busts targets as well as any out to 35 yards.
Even in that 5.5 lb single, recoil is minute.
In 20 gauge, I load up 3/4 oz loads using Hodgdon's data for Universal Clays.
They will not reset the triggers in my SKB O/U but work very well in an 870.