Originally Posted by
bjp
I have some loads for my 30-40 Krag for plinking/range loads, only doing 1700 fps which is fine for the range at 100m. But that's using a flake shotgun/pistol powder, another different rabbit hole to go down, so lets not go there at the moment!
2206H has pretty much run out at the moment, though hopefully we'll see it back on the shelves by the end of the year (or early next year, who knows). Not much if any 2208 around too. Lots of people use 2208, and you are much more likely to find someone willing to sell you a bit of 2208.
I'm a technical person, and I like to know how things work, and experiment (safely!). Using one of the reload modelling tools (GRT - Gordons Reloading Tool), it shows that slower powder (say 2209) needs more barrel time to get complete burn (compared to say 2208), which is accomplished by either a heavier projectile or longer barrel, compared to 2208 or 2206h. Hence why the recommendation for a faster powerder such as 2206h or 2208 for the lighter projectile.
For example, I use 2208 for 58gn projectile in my 243, but use 2209 for the 85-100gn projectiles. Barrel length is 22".
In my 24" barrel 308 I was using 2208 for 125gn projectile at 2850 fps, but was only getting 2550 fps in my 16.5" 308 with same load - the same velocity as my load with 168gn projectile. I now load the 125gn with 2219, and am getting 2820 fps from the shorter barrel, and 3050 fps in the 24" barrel (also its a hotter load). Longer barrel is still faster, but not by as much (230 fps faster powder vs 300 fps with slower powder).
When selecting a powder, I'm aiming for 95% burn or higher in the barrel in GRT simulations, on the simple theory (and I could be wrong) that a more complete burn in barrel should result in more consistent velocities, all other things being equal, along with it being an "efficient" load (i.e. you are burning powder to push the bullet, not just make a big muzzle flash!) Whether this is true in practice I don't know, but it seems to work for me. I'm also not chasing top velocities. I'm not a long range marksman (though definitely has some aspirations to develop), to me its more important to have accuracy/precision than speed. For hunting there are projectiles that will do what they are supposed to out to longer ranges than I can comfortably shoot, so appropriate projectile choice can make up for lower muzzle velocities in my case.
Looking at reloading data, most rifle data is for longer barrels (24") than most people seem to be using these days, so actual velocities will be lower than what's in the load data.