[bladesmith]

10-4. Years back I tried 800X in the 28ga using a Mec 650. I was getting drops all over the place, so I called Mec. He said because of such a small powder drop not to use a prgressive press but a single stage. Having just the 650 for 28 ga loads and 8 pounds of 800X, I did what I use to do 45 years earlier when I first started reloading. I would rap the side of the powder bottle when the bar was under it. That helped it fill that little cavity everytime. Ten years latter I still have a half bottle of 800X

 

[Silver_Is_Money]

I remember being frustrated with metering 800-X decades ago.

 

[Hal4son]

Next, you'll be telling me that you can't load a shotgun with black powder or pyrodex!
The topic is "low pressure" and some of us consider shotguns in the 1890-1900 time frame.

TRAILBOSS

What does anybody know about IMR trailboss? I have a little pressure tested data that was given to me in confidence so I don't feel at liberty to reveal the source. Hodgdons doesn't recommend using it in shotguns yet it has been done & is still being done successfully. My info. shows it yields...

www.shotgunworld.com

If you said "it's not suitable for a progressive press", I would agree with you.
If you said "I don't personally use any loads not tested and published by a factory", that's another thing to say.

If you have pressure tested data for Trail Boss or know someone that does, I'd like to see it.

I use a lot of Trail Boss in metallics. It makes a dandy 45-70 loading @ 1,050 fps with something around 12 grains of powder. It is not a low pressure powder and those are not compressed loads like you'd get with shotgun wads and typical shotshell loading. More to the point- Hodgdon states that compressing Trail Boss will make pressures spike to dangerous levels and specifically not to use in shotshells.

With that kind of warning from the source, I don't see how Trail Boss has any place in a "low pressure" load discussion without tested data.

 

[Hal4son]

... which presumes that with regard to reloading at intentionally low pressures (5K to 8K PSI) a fluffier low density flake type powder will be in general more accommodating of such low pressures (as regards maintaining consistent pressures and velocities at various extremes of temperatures) than would be the case for the various of denser ball type powders?

The king of low pressure past- SR7625 was very small flattened ball or tiny round flakes. I would call it the opposite of "fluffy" and utilized relatively heavy powder drops.

Some powders just seem to tolerate marginal pressures better than others.

 

[RMc]

... which presumes that with regard to reloading at intentionally low pressures (5K to 8K PSI) a fluffier low density flake type powder will be in general more accommodating of such low pressures (as regards maintaining consistent pressures and velocities at various extremes of temperatures) than would be the case for the various of denser ball type powders?

Perchance, you are thinking of a modern equivalent to Dupont Bulk Smokeless. Bulk smokeless was just that, loaded using volumetric dram powder measures. This powder was still around in the early 1950s as found in the 1951 THE IDEAL HANDBOOK NO. 38 (page 165).
See:
https://www.nzha.co.nz/wp-content/uploads/2015/08/IdealHandbook38.pdf

As far as lower pressure shotshell loading data with current ball powders, a 2019 Shooting Times article by Ross Seyfried remains the singular published source. The data includes loads developed with W572 and Hodgdon Longshot.

Comparative pressure tested Black Powder and even the long obsolete, Dupont Bulk Smokeless powder are included.
See:

Blackpowder Shotshell Loading Tips - Shooting Times

If you like light recoil, deadly performance, and classic guns, Goex Olde Eynsford black powder is just the ticket for your shotshell loads.

www.shootingtimes.com