Swiss, at least the 3fg, seems to be smaller grained than GOEX 3fg, from what I've experienced. I have two flintlock rifles that when I've used Swiss 3fg, they self prime the pan through the vent hole. This doesn't happen with either gun when using GOEX 3fg. I have to plug the vent hole when loading with the Swiss powder.
Mole Eyes
I'll have to explain it this way.
With my work on GOEX back in the 1990s.
3F powder is screened: 20 mesh top screen, 50 mesh bottom screen. Giving a "mean diameter" of 35 mesh.
Swiss #2 (3f) is screened: 18 mesh top screen, 32 mesh bottom screen. Giving a mean diameter of 25 mesh.
So based on screen size range used in production the Swiss 3f is slightly larger than the U.S. 3f.
Comparing the two. There will be more variation in size within different lots with the U.S. screen sizing. You can see "fine" lots and "coarse" lots in U.S. production where the differences are greater than what you would expect to see in the Swiss.
But then you have to deal with differences in the grains themselves. Compared to U.S. production the Swiss powders are more rounded. More smoothing of the grain surfaces and harder grain surfaces. This makes the Swiss powders flow better through hoppers, measuring devices, etc.
I got into this in depth with the old S/A Pernambuco Powder Factory. They produced safety fuse for blasting work. Fine grain black powder goes into a hopper on the fuse weaving machine. The safety fuse consists of a center thread surrounded by a thin layer of fine grain black powder that is encapsulated in a woven cover. If during the weaving the black powder fails to flow uniformly through the feed hopper you get a section of fuse that simply does not burn. Very dangerous in blasting work. So I had to coach them on how they polished the powder to get well rounded grains with very smooth surfaces that flow freely through the narrow opening in the fuse weaving feed hopper.
At Moosic. GOEX produced some lots of 2f and 3f where the grains were very angular, very sharp edged and very rough surfaces. Would not flow through a powder measure very easy. Yet screen testing showed the grain size range to be in specification. In all of my flinters I found that this sharp edge and grain smoothness thing showed up in how much 3F would come out the vent when I ran the patched ball down the barrel. You would see magazine writings where the target shooter would plug the vent with a round toothpick to stop it. Others thought it neat. With the frizzen closed it was described as self priming. While other shooters laughed because it would not work in their flinters.
At times I used this to judge if it was time to replace the vent liner. If I had main charge powder come out the vent when seating the patched ball I figured the vent hole had enlarged.
Oh. Almost forgot.
I mentioned how fast and hot the Swiss burns. In my flinters I found that the Swiss erodes vents a lot faster than slower cooler burning rifle powders. Then I thought back to late 19th century English writings on the use of platinum nipples on percussion guns shooting the good sporting powders of those days. The melting point temperature of platinum is well above the gas temperatures produced by a fast and hot sporting powder.
My industrial experience in PVC resin polymerization taught me that most stainless steels are easily eroded by hot gases flowing at high velocities. I spent a lot of time inside the reaction vessels cleaning them after resin batches were dropped out of them. A lot of interesting gas gouges in the thick stainless steel surfaces around the emergency relief lines.
Mad Monk
