With apologies to Pete for talking about him like he's not in the room, my take on his questions was why don't they give the groups and velocity spreads you're getting?
I'm trying to dissuade him from searching for the answer in seating depth or charge weight. He's inclined to replace the barrel, but I'm the wrong guy to ask because that's pretty much my standard response to most problems. I have a lathe in the garage and really shit on my barrels with much longer strings than you shoot. I'd never start a cross country trip with a 375CT barrel that had 600 rounds through it.
I've sorted 100 ct boxes of 230 hybrids and had 3 that were a couple thou longer than the 5 thou group the rest of them were in. I threw them back in the pile and used them as is. I've had 300 grain 338 boxes that were 35 thou end to end. If the guys using the 410s report the length variations they see, it'd be helpful but sorting hybrids by length or trimming them is how I've used them in the past. I don't see the 410s being any different.
Litz's second Modern Advancements book had some BC variation data in it including the impact of trimming and pointing. The third had a bunch of even better testing and correlations to popular sorts. The anchor number of 1% per 10 thou OAL was for a specific bullet. Depending on how it's scaled, it might be half or twice that for another bullet. I'm betting half for the 410, but could easily be wrong. The twist is the correlation only works half the time. Sorted bullets will likely give better vertical beyond 2000 yards. Enough likely that it'll be probably be worthwhile often enough to justify the effort. Sorting 500 bullets on length with a set of calipers just doesn't take that long in the grand scheme of things. For me anyway, but I'm retired.
On the 3 boxes to check, I think I've posted this one before.
It's the error budget for a pretty good 375CT. The precision line is for 1 moa. Making it 1/4 moa is a rush at 100 yards but not much use at 2500. The other lines are for 15 fps and 1.5% on the BC. I use 10 shot strings as a standard.
I shot 250 ATips at 2580 yards last Friday. The wind was gusting from 5-15 mph and during my last string it went from 5:00 to 11:00. There were 0.6 mils of vertical in that wind shift, about the same as 2% on the BC. 15 fps on the velocity gave 0.4 mils. Not a good day for checking BC spread. It was a good day for cheaper and simpler reloading.