Well, because I wasn't happy with the results I received, I shipped 3 more samples to Tom Armbrust for testing. By reducing the grains of powder, I was able to drop the pressure. Unfortunately, the velocity is probably too low. I'll share my results:

16 ga. RST Hull, 2 1/2", Cheddite 209 primer, 13.5 gr of Green Dot, SG16 Wad, 7/8 of #8 shot produced 8,500 pressure and velocity of 1,082. Not Bad!

16 ga. RST Hull 2 1/2", Cheddite 209 primer, 11.0 gr. of Green Dot, SG16 Wad, 7/8 oz of #8 shot produced 6,500 pressure and velocity of 931. Pretty slow.

16 ga. RST Hull, 2 1/2", Cheddite 209 primer, 10.5 gr of Green Dot, SG16 Wad, 7/8 oz of
#8 shot produced 5800 pressure and velocity of 875. I'll probably be able to see the shot string leave the barrel.

The first sample using 13.5 grains of powder generating 8,500 psi is probably usable, but a little high. For comparison purposes, let's look at RST. A 16 ga. RST Falcon Lite uses 7/8 oz of shot and it has pressure of 5,400 and velocity of 1125. NICE! I wish I knew what powder they use.

I suppose I could drop down to 3/4 oz of shot. That would probably drop the pressure a little. Any suggestions?

I have found some recipes that achieve pressures in the 6000-7000 range, but they require SR 7625 powder and I have not been able to locate any. Sincerely, Jeff

I’ve probably got close to two thousand 16 gauge 1 ounce loaded with SR4756 and using the SP-16 wad in the old smooth WIN AA style 16 gauge hulls that’s a soft target breaking load . Only problem like 7625 , 4756 is just as difficult to obtain . Luckily I’ve got a good supply of 7625 (none for sale) . But my 7625 is for all 10 gauge loads as well as buck/slug loads for the 12-16 and 20 .

roll crimping might lower the pressure further, but a different powder would likely be a better bet if you want super low. UNIQUE is still available and it is what I intend to use as a substitute for 7625 and universal.
I have wondered if the rst pressures are slightly more these days with component changes?