Guy's,
Let me preface this post with the disclaimer, that I DO NOT own stock in either Goex or Swiss Powder. I do not have a dog in this fight.
Now with that said in my experiance Swiss powder is so far ahead of Goex it aint even a fair race. There has been much written about the differences in these two powders. Well these differences are really pretty simple Goex powder has a "Musket Burn Rate" and Swiss has a "Sporting Rifle Burn Rate" these are scientific designations and what they really mean is Swiss powder is very close to the powders of old in burn rate. I am not saying that Goex won't work in a cartridge rifle it goes bang every damn time. But it fouls more and a lot more in some cases, and is not capable of the velocity's you can get with Swiss becuase Swiss is true Sporting Powder.
I am a Silhouette shooter and as such I shoot a lot. Practice for me is at least twice a week and I really prefere three times if possible. I shoot a minimum of 150 shots in each practice session. I then shoot a Silhouette match every weekend almost year round. That is at least 400 rounds a week or 1600 bullets down range per month. I use a hell of a lot of powder, primers and lead--way to much. When I first started shooting I was using Goex 2 fg in my Meacham Highwall. With all of the shooting and going thru that much powder I was ordering powder by the case every 3 months or so. With the Goex I had to start load work up all over every time I got a new case of powder. No two lots where ever the same and some times I would have to go thru 4 or 5 lbs just to get a desent load. When I found out about Swiss I ordered a case and loaded it the same as I loaded the Goex. That was a lot of compression like .350. The Swiss fouled so bad I was ready to use the rest of that case on the lawn. A friend advised me to use little or NO compression and see how that worked. I loaded up a hundred with NO compression and damn how this shot, almost no fouling at all. To clean one wet patch and a couple of dry patches and I was ready to go again. When I had to order my next case it was the same lot as the first and shot exactly the same. It was 5 cases later before I got a different lot, loaded it as the old lot and found no change at all, it shot just the same as the first lot. WOW!! I now have had some of all 4 of the different lots of Swiss powder, the powder did change on the latest lot. This new Swiss is not quite as dense as the old stuff and weighs a little different, but it shoots almost exactly the same no load change at all. I have found it to be a little faster than the old stuff but that is fine with me.
If you look at the people who compete on a regular basis you will see that Swiss is used by these competitors 10 to 1. For the last two years at the BPCR Nationals the total of Goex users was about 30% with 70% or so using Swiss. In the winners circle last year at the Nationals had 9 of the top 10 shooters using Swiss, Goex had only 1 finisher in the top 10. The year before last was the same 9 of the 10 where using Swiss. This ought to tell you something.
Now your original question was about granulation size to order for your 45-70. I have played a little with 3 fg Swiss in the 45 and really found no advantage to this grain size, you will get a little more speed from the 3fg but with that comes a price, that price is more fouling to deal with. Swiss 1 1/2 is damn good powder for the 45-70 it needs no compression or very little to shoot well, fouling is not bad at all and clean up is easy. I am one of the few Silhouette Shooters using 2fg, I have found it to shoot a little flatter than 1 1/2 and not have the fouling of 3fg, for me it works just great and I would encourage you to give 2fg a try. But if you have your heart set on 3fg go for it you will find Swiss powder to be another world away from Goex.
Gunny