Accuracy=seating depth or tenths of powder

[NATE40]

It has all to do with seating depth. I worked my load up to where I use the seating depth to add more powder to the case and increase mv while keeping pressure to a very exacting max for the rifle. My load development stopped when the primers started to a light strike flow. Increasing seating depth Evan by 3/1000th this flow started to become more dramatic my choice to stop at this point was that's as far as I wanted to push my rifle to just make a stupid point. I find it hard on websites to post findings and tips when everything must be challenged instead of people doing research on a subject and posting their findings. A point was made I took it with a grain of salt and tested it. And posted my finding that's it. Not mad and I don't feel like I'm casting my pearls before swine because there are people who will use open minds and use what they read to investigate instead of trying to make their point so much instead of learning something

 

[Pdvdh]

Your findings were obviously good enough for your own purposes.

Don't let our banter interfere with your forward progress.

 

[NATE40]

Thanks for the post, and your right everyone has their own goals and purpose and I enjoyed reading your posts so much I had to try it. Lol

 

[baldhunter]

Here is a good read on this subject.
Internal Ballistics - Hornady Manufacturing, Inc

 

[Bart B]

That link to Hornady's site with info on resizing cases has a few flaws and errors.

Hornady calls "headspace" incorrectly according to SAAMI specs as well as most folks. It's correctly called "head clearance." Chamber headspace is the distance from the breech face to the point in the chamber that stops case forward movement from firing pin impact.

Hornady stresses the importance of full length sizing being limited to only a few times per case. People setting up standard full length sizing dies to resize fired bottleneck cases from SAAMI spec chambers such that their shoulders are bumped back .001" to .002" fifty to one hundred times. Yes, they need to be trimmed when they grow to max length so there's at least .010" case mouth clearance to the chamber mouth.

 

[baldhunter]

You need to send them an email and get that corrected.

 

[Pdvdh]

Here is a good read on this subject.
Internal Ballistics - Hornady Manufacturing, Inc

I found and read the portion of the Hornady article (from the link) related to bullet seating depth and pressure. I think they got that part of their article correct. Thanks for sharing that link.

 

[Bart B]

I've sent Hornady a couple of emails on that subject over the years.

Last summer while touring their Nebraska plant, I mentioned it to the two people in their reloading room loading ammo to test bullets. I was politely informed by them that I was wrong.

Sierra Bullets' reloading manuals' section on reloading have had in print comments that rifle cartridges rest in the bottom of the chamber when fired. I don't know if they've corrected that.

 

[BountyHunter]

Interesting discussion as each barrel has its own quirks and at times anything works or does not.

However you might want to look at what the top LR world class shooters are doing and why and their results in relationship to this discussion.

They sure make working powder and then seating depth work and they tell you why and how. Pretty sure they would love to discuss why you should work seating depth first if you can convince them.

I have tried both and I can always get powder and seating depth later to work with minimal effort so I keep using it.

What is interesting for the people who want to really learn is the use of target scoring software and graphing results to show what is actually going on instead of what you think you see sometimes.

Erik Cortina who first posted his method, is the captain of the lapua brux F class team, so definitely knows LR accuracy and load development.

Long range load development at 100 yards.

Anyway just a description in detail of how powder and then seating works for the professionals.

 

[Bart B]

All this talk of load workup is interesting.

I've never worked up any load for 308 Win or two 30 caliber magnums with Sierra or Lapua match bullets across different makes of match barrels. Just used the same loads the winners did. Accuracy tests with them equalled theirs. One exception was for a new Sierra match bullet for which no data was available.

Being a firm advocate of shooting enough shots per test group to have at least 90% confidence of representing the accuracy all rounds for that recipe will have, I've concluded that 100 people given the same components and rifle shooting one 5-shot group with several combinations and assemblies, there'll be 100 "most accurate" loads and no two alike.

Regarding the above link's tests with 3-shot groups. People who've shot dozens of 3-shot groups in controlled conditions (indoors with free recoiling rifles) have groups with the largest one 4 to 5 times bigger than the smallest. And the first one shot is seldom the smallest one and all group centers aren't at the same place. Most folks think otherwise; one 3-shot group'll be the same size and at the same place as several of them.

 

[Bart B]

One interesting observation I've nor seen across hundreds of ways to determine the best bullet seating position relative to the rifling is throat erosion.

What does one do as the rifling erodes away .001" increasing bullet jump that much every couple dozen or so rounds? That's the typical rate burning powder erodes away the rifling. It's easy to measure over the life of the barrel.

Do you seat bullets .001" shallower that often?

How much does your accuracy degrade if you don't?

 

[Pdvdh]

Good point. If seating depth control on the order of equal to or less than 0.001" is ultra critical to optimum accuracy, it seems this would have been discussed. Maybe we don't understand what we thought we did about seating depth sensitivity?

 

[barefooter56]

Good point. If seating depth control on the order of equal to or less than 0.001" is ultra critical to optimum accuracy, it seems this would have been discussed. Maybe we don't understand what we thought we did about seating depth sensitivity?

I think you would really have to have a hugely overbore cartridge rifle burning a fast powder to erode a barrel throat that quickly (.001 per couple of dozen rounds or so). When I was shooting PALMA my average on a Kreiger barrel / 1-13 twist/ 30 inch finish, using (then) a SIERRA 2155 155 grain bullet ( hard jacket) and N-550 powder ( thought to be very erosive by some) pushing that bullet at 3030 fps. My throat erosion over the course of a season ( usually 10 matches plus the nationals) and practice , ( 10 matches at 60 rounds per match including sighters plus the nationals about 300 rounds including sighters = ABOUT 900 rounds plus practice I put about 1200-1300 rounds per year down that barrel and only averaged about .010 at most. Some of that practice was seating depth testing during the season. Must have had a pretty wide seating depth accuracy node because I only had to adjust the seating depth about .002-.003 over the course of the season. Powder charge was tweaked slightly to stay on velocity node. But that was THAT rifle barrel. Hunters may go a lot longer and benchrest shooters a lot shorter in time span before noticing any fall off in accuracy where they have to adjust something. IMHO is that seating depth sensitivity should be taken on a case by case basis depending on what you are using the rifle for , how much the accuracy falls off and how much accuracy for what you are using the rifle for is needed/wanted. That being said. A known seating depth accuracy node can only help when doing any accuracy diagnosis down the road. thoughts?

 

[Pdvdh]

Excuse this question if I should already know, but what cartridge were you using when experiencing the throat erosion rates you describe? Trying to put some context to those throat erosion rates in comparison to the cartridges and powder charges I use for LRH. Thnks