How far off the lands do you start?

[Harvey_NW]

As another data point, among many, is this comparison of 3 shot ladder tests to find nodes in a 308 hunting rifle backed up with larger groups that also confirm the same best and worst nodes. One set of tests was 800 rounds ago and it’s duplicated now for comparison. He does a good job of summarizing EC and what the Hornady boys have said, with what is seen in his rifle.

His takeaway is it made about 1/4 MOA difference, which may or may not be worth the time and money to shoot it for someone else.

This is a good video, but it's still drawing conclusions from groups without applying the variability. I'm not a statistician, so I'm probably messing this up. Maybe @solarshooter can chime in with corrections, but this is where my head goes when I watch this video-

Hornady says there's still 20-25% variability in 20 shot groups, and 15-20% in 30 shot groups, even 10% still in 50. The way they explain it is that percentage stat is +/- from an average. Since this is a single group and not an average, one would have to consider the possibility that it's on the low end of the expected spectrum, so it could have ~40+% increase (splitting the difference using 20%) if repeated, so ~1.2", very close to the other group.

Factor in shooter ability, weather, fatigue, and 50 rounds out of a bare muzzle 308, and there's just not enough there for me to conclude that one seating depth was actually better than the other.

 

[TaperPin]

This is a good video, but it's still drawing conclusions from groups without applying the variability. I'm not a statistician, so I'm probably messing this up. Maybe @solarshooter can chime in with corrections, but this is where my head goes when I watch this video-

Hornady says there's still 20-25% variability in 20 shot groups, and 15-20% in 30 shot groups, even 10% still in 50. The way they explain it is that percentage stat is +/- from an average. Since this is a single group and not an average, one would have to consider the possibility that it's on the low end of the expected spectrum, so it could have ~40+% increase (splitting the difference using 20%) if repeated, so ~1.2", very close to the other group.

Factor in shooter ability, weather, fatigue, and 50 rounds out of a bare muzzle 308, and there's just not enough there for me to conclude that one seating depth was actually better than the other.

You and I will just have to agree to disagree. He shoots that same 308 a lot, has plenty of 10 shot groups around 1/2 MOA in other tests so he seems more capable than the average guy, the wind conditions as stated were quite good, he doesn’t throw out fliers to alter the results, and all the shooting he did for this video was duplicated at an earlier date, which doubles the round count.

Beyond that, there was no doubt in my mind going back 30 years ago seating depth can fine tune a load based on extensive shooting by others, so what he did is more or less what I’d expect.

Not much in reloading is brand new never been discovered before. Powder charge makes a larger difference, but all the accuracy minded shooters I know do a seating depth test after settling on a powder charge. Not one out of a hundred, or twenty, but all of them.

The guys I know that reload for hunting don’t usually find the effort worth the results, partially because their rifles aren’t very accurate and seeing trends through the fog takes higher round counts, and partially because the accuracy achieved with varying the powder charge is good enough.

If long bullet jump didn’t have any effect on accuracy we’d all be shooting rifles with gigantic freebore built into the chamber like the Weatherby cartridges where 1/4” bullet jump isn’t uncommon. We’d be able to get a little extra velocity at the same pressure level and same COL.

The Hornady guys have come out and said what they focus on is information for average reloaders and does not fully translate to the accuracy sports. They are very much in advertising and while much of what is said sounds objective their comments are carefully crafted and often leave gray area in how it’s interpreted. At the end of the day their #1 job is to encourage the average reloader to be happy with their Hornady products and buy as much as possible.

 

[TaperPin]

That video is well done. For those not watching the video: he selected a seating depth using Cortina's method and then loaded 25 of those. He then picked the "worst" seating depth identified by Cortina's method and shot 25 of those 5, 5-shot groups of each he compiled into a composite group of 25 for each load. Very similar to what I challenged the OP to do seveal posts back. The "good node" group measured 0.861" with a mean radius of 0.287" while the "bad node" measured 1.129" with a mean radius of .332." Good shooting.

If I had gone to that trouble, I would definitely pick the seating depth that shot smaller in the test. Confidence is worth having. But . . . it's worth remembering that one should expect about 20% variability in size of even 25-shot groups. Is one group actually better than the other? Maybe? Probably a little? (I'm sure there's a statistical test that can actually asnwer that question). Is it worth your trouble? If I put 25 shots in 1.129" I'm rolling with it.

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It shouldn’t get lost that generalized tables and expected extreme spreads can not describe a specific rifle and load, any more than statistics about average families describes a specific household, and shouldn’t be treated as such. Some rifle/load combinations are very consistent and some are very sporatic, so trying to estimate what a specific rifle will do based on computer simulation dispersions is a poor decision making tool. These are well meaning and do help people visualize the concept, but many barrels are burned up every year that don’t follow these simplistic percentages, not by a long shot. These remind me of something Brian Litz would put out.