[Jim Atlas]

If the local guy has 800x, get it. Before Alliant Steel powder, 800x was one of the best powders for what you're trying to do, along with 4756 (or so I'm told, I wasn't reloading then). Unfortunately, neither are made anymore, so get it! 800x may present some trouble if you try to drop powder charges using the lee load all. By the way, you'll have to hand weigh the #3 steel shot too.
I have run across some hs6 steel shot data, but it uses a wad that's out of production. So you may have to send a load with a wad you can get to get pressure tested.
Problem with longshot isn't that it loses velocity quicker (not sure how that'd even be possible), but that it develops pressure faster as you increase the powder charge. But it can make steel loads, you just have to respect that.
Honestly, Alliant Steel is the best powder for the job. You just have to keep looking. Till you find it, I'd try 800x and blu dot (also hard to find).

 

[Jim Atlas]

I was going to say if you found 800x you’d better grab it.

100%

 

[Jim Atlas]

I wouldn't say avoid longshot by any means. Just understand that it can get away from you.
As to being economical, if that's a major consideration, I'd rethink reloading. You can save money reloading, but you'll end up spending those savings on components and equipment.

 

[Jim Atlas]

Problem with BPI is too many of their loads don't make sense. I'm stuck in a hotel in Wyoming, so I can't get to my reloading books to pull up examples. But there are a lot of head scratchers when compared to data from Alliant, lyman, pri, and rsi. Heck, their are a lot of question marks when comparing BPI loads to BPI loads. The first steel load I every tried loading was a bpi load; 2.75" 12 ga fio case with an impossible amount of powder and shot. Couldn't get it to fit. Still can't get it to fit. It gives the impression that their testing may not extend all the way to actually assembling the load...
I'm not saying their data is all worthless. I'm only saying be smart and crosscheck it. And you can always get a load tested...