Crazy lot-to-lot consistency with Staball Match?

[FrontRange]

So, I’ve been using Staball Match for a couple of different cartridges (6.5 Grendel, 6ARC, AND 223) and have been generally quite pleased with velocity, temp stability, accuracy, and sds. I bought another pound and loaded some 6.5 Grendel with an established 31.0gr load at 2420fps (inline with Hornady and Sierra data) without worrying too much about lot differences and needing to work up because of the relatively low pressure in a gas gun. However, I didn’t expect a 120fps DROP in velocity. I went home and checked my charge weights (they were the last charges I dropped) and, right on the money, 31.0. This is basically a full case up into the neck so I don’t think I can get much more powder into it. I haven’t tried this lot in any other cartridges but, at worst, I can use it for 223 practice. I’ve never had anything like this happen at least not anything that changed velocity by more than 50fps. Thoughts? Does this happen? Thanks, I’m a little at a loss?