I'm actually using the magnetospeed doing a ladder test based on muzzle velocity. I've done it a handfull of times and although I'm still pretty new to the theory of it, there does seem to be something to it. I've done several ladder tests between my .308 and my wife's .270 and have come away with some pretty good loads to refine - one being 165gn Federal TBT's in front of 43.3gns of H4895. I've followed up a couple times on that one and it's consistently about .75 at 100yds.
My distance on this one is only 100yds and the pic of this target uploaded sideways (you can see a slight trend of vertical stringing, but only very slight). I used 21 rounds on this ladder test because I was using Big Game, a spherical powder, and its different from the stick powders I've worked with in the past (Varget, H4350, H4895, H4831SC). I went exactly with the load data published on Nosler's website for the 140gn AB's in 7mm-08 which ranges from 43.5gn (min) to 47.5gn (max). All the velocities published are something I'd be happy with in this rifle, so I just decided I'd run the entire range to see what might happen; started at 43.5 and increased each successive charge by .2gns for a total of 21 rounds. I record all the MV's and in the analysis afterward, look for places where the velocities don't change much, like 5-10 fps between 3 shots.
When I've done this in other rifles, I generally used a dozen rounds because I'm more familiar with the velocities the powders would produce and have a better idea of what I'm looking for. Even with those dozen or so rounds, you can see some trends - stringing and such - at 100yds, but they certainly don't all go into the same hole like this one did. I haven't really poured over the velocity data yet, but I'm feeling pretty confident I'll be able to find a really good load out of this.
This is all pretty interesting stuff. I should have started handloading years ago.
