Seating Depth Method of Tuning Load.
- Thread starter BCBRAD
- Start date
I do both. Typically I measure the distance to the lands and do my first load development .020 off the lands.
I pick a charge based of those results, and I do another round, this time varying the seating depth.
Then I do a third round, using the seating depth I found worked best in round 2, and fine tune the powder load a little up and little down.
There may be a better way of doing it, but I have been able to get all my rifles to shoot sub MOA doing it that way, and .7 MOA vs .8 MOA isn't worth the stress, I'd rather shoot and focus on better form then continually chase better loads.
I pick a charge based of those results, and I do another round, this time varying the seating depth.
Then I do a third round, using the seating depth I found worked best in round 2, and fine tune the powder load a little up and little down.
There may be a better way of doing it, but I have been able to get all my rifles to shoot sub MOA doing it that way, and .7 MOA vs .8 MOA isn't worth the stress, I'd rather shoot and focus on better form then continually chase better loads.
You are leaving knowledge on the table.
If you have a laod that works well, try the same bullet in the lands square. (Rifling marks are as deep as they are wide). And also try laod just barely off the rifling.
Of the 3 loads, one might be better than the other.
The "into" the rifling load has issues. If you open the bolt, the bullet may pull out of the case and dump powder. No good for a hunting round, for sure.
If you have a laod that works well, try the same bullet in the lands square. (Rifling marks are as deep as they are wide). And also try laod just barely off the rifling.
Of the 3 loads, one might be better than the other.
The "into" the rifling load has issues. If you open the bolt, the bullet may pull out of the case and dump powder. No good for a hunting round, for sure.
I've been working on the assumption that a particular pressure will beget a certain velocity. This velocity with its attendant rate of acceleration in the bore may coincide with a node if the powder charge is correct for attaining such.
I have not fiddled with seating depths except for COL fitting magazine or between 10 & 15 thou off the rifling if it does.
I have been using QuickLoad for load development and it does not hint at any particular seating depth being good or bad, but as long as it is known then it can be entered into the calculation.
Is seating depth used to fine tune when other parameters are unknown?
hometownhero
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Seen loads go from over Moa to well user and all that changed was seating depth. It is a good test to do and really tighten things up
I think seating depth is more of a function of the bullet than the rifle. I load Sierra match bullets at 20 thou off the rifling and have never found that other depths make much difference.
But I have used some VLDs where the popular wisdom was that they work best on the rifling. I tried that and found no difference, but the point is - I tried it.
If you have a load that works and is near max, seating a bullet into the rifling is probably going to make it worse. i would try it at a half and full grain less than usual, just to be sure you are not getting a potential bug hole group load.
And then there's the barns X bullet , they recommend 50thou jump and I've found thats their best accuracy in my rifles
Also as granderite says every bullet I try likes its own depth from the lands - sometimes it's a very noticeable difference
Long range load development at 100 yards.
Erik Cortina Team Lapua USA
http://forum.accurateshooter.com/threads/long-range-load-development-at-100-yards.3814361/
"Some of you have asked for more detailed instructions on how I do this. Here they are:
1. Find Jam by seating a bullet long on a dummy piece of brass (no primer nor powder) and apply die wax to the bullet ogive and record it's base to ogive length.
2. Chamber the round and close the bolt.
3. Snap the bolt open and measure the base to ogive measurement. If it is shorter than previous measurement, this is your jam. Do it a few times with different cases to make sure.
4. Load a known powder/primer/bullet combination. I load 4 of each powder charge in 0.5 gr. increments and seat bullets at jam - .020". I use one shot of each to get barrel fouled up and also keep an eye for max pressure at the same time. You can also use these rounds to break in a barrel if you are inclined to. If I encounter pressure on the hotter rounds, I will not shoot groups with the other loaded rounds and will pull bullets when I get back home. Do not shoot in round robin style because position and natural point of aim will be compromised.
5. Shoot 3 shot groups starting from lowest to highest. All groups are shot over a chronograph.
6. Examine target and find the place where consecutive groups line up vertically and ES is the lowest and speed increases the least from one group to the next.
7. Load to the middle of the powder node and do a seating depth test.
8. Load 3 shot groups starting from Jam - 0.005" all the way out to Jam - .040" in .003" increments.
9. When you find the seating depth test that shoots the best, load towards the longest side of the node to allow more room for throat erosion.
10. Final step is to load the new seating depth and load 5 shot groups in 0.1 gr. increments 0.5 gr. on each side of node (if pressure limits are not reached). This will cover an entire grain of powder and you will be able to pinpoint where the powder node starts and ends. In the summer, load towards the low end of the node, and do the opposite in the winter."
Erik Cortina Team Lapua USA
http://forum.accurateshooter.com/threads/long-range-load-development-at-100-yards.3814361/
"Some of you have asked for more detailed instructions on how I do this. Here they are:
1. Find Jam by seating a bullet long on a dummy piece of brass (no primer nor powder) and apply die wax to the bullet ogive and record it's base to ogive length.
2. Chamber the round and close the bolt.
3. Snap the bolt open and measure the base to ogive measurement. If it is shorter than previous measurement, this is your jam. Do it a few times with different cases to make sure.
4. Load a known powder/primer/bullet combination. I load 4 of each powder charge in 0.5 gr. increments and seat bullets at jam - .020". I use one shot of each to get barrel fouled up and also keep an eye for max pressure at the same time. You can also use these rounds to break in a barrel if you are inclined to. If I encounter pressure on the hotter rounds, I will not shoot groups with the other loaded rounds and will pull bullets when I get back home. Do not shoot in round robin style because position and natural point of aim will be compromised.
5. Shoot 3 shot groups starting from lowest to highest. All groups are shot over a chronograph.
6. Examine target and find the place where consecutive groups line up vertically and ES is the lowest and speed increases the least from one group to the next.
7. Load to the middle of the powder node and do a seating depth test.
8. Load 3 shot groups starting from Jam - 0.005" all the way out to Jam - .040" in .003" increments.
9. When you find the seating depth test that shoots the best, load towards the longest side of the node to allow more room for throat erosion.
10. Final step is to load the new seating depth and load 5 shot groups in 0.1 gr. increments 0.5 gr. on each side of node (if pressure limits are not reached). This will cover an entire grain of powder and you will be able to pinpoint where the powder node starts and ends. In the summer, load towards the low end of the node, and do the opposite in the winter."
I found the best groups with the Nosler Accubond when they were seated 100 thou from the lands. I start load development with all bullets 20 thou back and find the best powder charge and then try the same load 80 thou back and 100. I find small increments don't change much. Factory cartridges have to fit all rifles and are seated with lots of jump.
This has been my experience also. The difference in group sizes between 0.005" jump and 0.030" jump hasn't been worth talking about. Once I got beyond 0.040" of jump the groups opened up a bit.
The average distance deer are shot in the woods of central Pennsylvania is 40 yards.
And in 1973 when I started reloading with my new Rockchucker press I pondered about seat length.
So to keep it simple I bought Hornady bullets and seated the bullets to the middle of the cannelure.
The only measuring tool I had at the time to measure OAL was a green plastic Lyman vernier caliper. And I got tired of counting all the lines on the scale.
I'm retired now and have been reloading for over 47 years and have too many gauges.
And now I remember the good old days when life was simple and the green plastic Lyman vernier caliper I hated to use.
And in 1973 when I started reloading with my new Rockchucker press I pondered about seat length.
So to keep it simple I bought Hornady bullets and seated the bullets to the middle of the cannelure.
The only measuring tool I had at the time to measure OAL was a green plastic Lyman vernier caliper. And I got tired of counting all the lines on the scale.
I'm retired now and have been reloading for over 47 years and have too many gauges.
And now I remember the good old days when life was simple and the green plastic Lyman vernier caliper I hated to use.
"The average distance deer are shot in the woods of central Pennsylvania is 40 yards."
I don't know the average for Ontario, but I doubt it is far as 40 yards.
My personal longest is 125 yards, but most have been 25 or less.
I sit and relax and let them come by me.
I don't know the average for Ontario, but I doubt it is far as 40 yards.
My personal longest is 125 yards, but most have been 25 or less.
I sit and relax and let them come by me.
Seating depth changes of 0.003" at a time. 3 rounds each. At least a string of 6 different seating depths. Start from jam or mag length. Any wider changes will skip past the accuracy nodes till you get lucky and eventually hit one. Do this at 200 yards or more if you can.
Seating depth can be a source of accuracy if you want to chase the absolute most. I bought one of those Hornady modified case and OAL length tools and it made it really easy to find the lands. But, if you rifle shoots factory ammo which is loaded to SAAMI specs insanely well is it worth chasing? Maybe not. But it can help. Another function atleast for me as I'm not huge on compressed loads sometimes seating closer to the lands has the added benefit of making a slight decrease in powder compression in my 185 Gr Juggernaut OTM 308 Win loads. These are very specific loads I run and sometimes I kind of wish I didn't, but the rifle shoots with the bullet really hanging out there.
