Thread: "Extreme Velocity Spread"!

I have had similar velocity spikes when seating projectiles to touch. I have since found that it is better to either jam them by 0.010" or jump them by at least 0.015". I suspect that a combination of the Hornady comparator (+- 0.003") and the usual variation in projectiles (+-0.002"), some of yours will be touching more than others. When seating it pays to measure each round and back off the seating die before seating the next projectile. Also as mentioned try 2217 or 2225. One thing I have found to reduce ES is to use a large rifle primer instead a magnum one, but this was in a couple of 7mmRM's. I used to use a heap of SST's but found quite a large dimension variation in them from box to box, and occasionally within on packet. So I stopped buying them.
The ES you are getting is probably a combination of several slight variations, but seating depth would likely have the biggest effect.

I forgot to add. I also found that SST's can like a large jump. Try seating a few to the canilure. You might be surprised. Good luck.