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Load development with SEATING DEPTH first

Hengehold

Silver $$ Contributor
I recently received some reloading advice from one of the prominent bullet making companies that we all use. The advice was to begin load development with a moderate powder charge and shoot for groups by adjusting the SEATING DEPTH and leaving the moderate powder charge constant.

For example, shoot 5 shot groups of the following:

.010 jam, 45.0 gr Varget
.005 jump, 45.0 gr Varget
.040 jump, 45.0 Varget
.070 jump, 45.0 Varget

After testing different seating depths, Pick the seating depth that resulted in the best group. The second step is to adjust the powder charge while keeping the seating depth constant.

For example let’s say .040 jump provided best groups in the initial testing of seating depth. Now we will shoot 5 shot groups with the following:

.040 jump, 45.0 Varget
.040 jump, 45.3 Varget
.040jump, 45.6 Varget
.040 jump, 45.9 Varget
Etc.

I have never considered using seating depth as the first step to find the tune of a barrel. I have always done load development the other way around with adjusting the powder charge first and then fine tuning with seating depth.

Question: Does anyone else here prescribe to the “seating depth first” approach to load development?

My background is in NRA high power competition. Maybe this is something that is common among the benchrest community?

Thanks,

-Trevor
 
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All my junk is factory, but I like to do a coarse seating depth test first. Mine usually is from 0.005 jump to 0.030 jump with hopes of finding something that stands out compared to the others. That said, my attempts at load development this spring has in a word.... sucked!
 
I’m interested in bullet jump. And weight. These are a serious questions.

How do you determine jump, and how do you factor in weight?

I ask because I once spent time measuring the distance between a bullet’s base and its ogive.

I did this using bullets from a few different manufacturers with bullets of the same weights.

1) Obviously, and irrelevantly, the difference in jump between bullets from different manufacturers were different.

2) NOT obviously (until I thought about it), bullets from the same lot number from the same manufacturer . . . varied by several thousandths.

3) If you weigh bullets from the same manufacturer from the same lot number, is there any difference? Well, I found there are!

4) So how do you balance different “jump” distances against different weights unless you sort bullets by both, individually, and compensate when there are disparities?
 
I think that it can be fairly stated that the important distance is not between the base of the bullet and and its ogive, but rather the distance from where the seating stem makes contact on the ogive and where the rifling would first touch. In any case even with unsorted bullets, if you seat them all long and group them by their head to ogive measurements, you can then do a final seating for each group with individual adjustments of the seating die for each, depending on how much deeper that group needs to be seated. Beyond this, Berger states that for jumped bullets the nodes are so large and robust that the initial test can be done with changes of .040, which would of course be both ridiculous, and impossible when working from touch, extending farther into the rifling. Here is a link to that article.
https://bergerbullets.com/vld-making-shoot/
My point is that at least for this first test, differences in bullets shapes of bullets from the same lot are unlikely to matter. Of course once the general location of a node is determined, that would be another matter.
 
Hengehold said:
Question: Does anyone else here prescribe to the “seating depth first” approach to load development?
Click to expand...

No jam in factory chambers.

I start with a basic OAL. Bullets bearing surface in full contact with case neck. Must fit magazine and not jam.

Then try different powders and amounts. Pick the best one , now fine tune neck tension/OAl. Working with .010" increments, 2 longer, 2 shorter , test on target.

Tension will change when less bullet shank is in contact with case neck. Like here. a.jpg If this bullet is seated deeper, neck tension will increase.

More neck tension raises bullet pull. .002" NT = about 35 pounds BP. (223)

Bullets pressure ring, if bullet has one- i like to have it not in contact with the neck. Deeper into the case, shorter OAL.


I would not work up to a maximum powder charge using a jump , then change to a jam. Jam raises pressure.

Jam is for custom chambers. I remember having to unload a jamed 243 with light neck tension . Bullet stayed in rifling and IMR4350 spilled all over.
 
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Base to bullet OGIVE is far more important than seating stem contact. The bullet OGIVE is what hits the rifling and determines jump.

If you are really going to find a good load you need to ladder test and find the nodes. Moderate loads won't get it done. Sure you may get lucky, but you won't find what is best for the rifle. Barrel length matters as you may have 2 or 3 nodes.

Shoot ladders in 5 shot groups, 0.1 grain increments. Keep an eye on average velocity and SD. When velocity is climbing slowly and SD's are under 10 (under 6 if your scale reads 0.00) then you are on a node. When velocity is climbing or dropping rapidly, it is a place you don't want to be - you should only have slight verticles in your groups. Once you find the nodes, adjust your seating depth to clean up the L-R in the groups. If things are not working out, try a different bullet.

Don't do this with NEW brass. New to the rifle and FLS is okay, but new brass itself typically has a lot of movement so it won't yield the consistency that is needed.
 
I find the bullet I am going to use and I have the barrel throated to this bullet.

I make sure most if not all the "bearing surface" is in the neck. I use the "cut neck" process to determine the when the bearing surface is exactly where I want it in the neck.

When dialing in, I determine which load is working the best for me and my rifle. All barrels are different. I believe I have lucked up 3 or 4 times and my replacement barrel handled my load perfectly.

At this point in my dialing in process, I start playing with seating depth. NOTE: Pressures increase the closer you get to the lands. So I start @ .050 off the lands (I also chrono every load, speeds, ES, & SD, consistency). I then go in .010 increments out to .080. After seeing how these rounds fire, and make sure there is no pressure signs, I then set the bullet .040 off the lands, then .030 off the lands, and if no pressure signs are showing, I go all the way to .020 "IN THE LANDS".

"I was shocked" when one of my barrels "loved" the bullet .050 off the lands. It was a mistake when this happened, I didn't mean to set them .050 off. This barrel remained a "tac" driver until I wore it out! I did set it back and had my original results for another 1,200 rounds or so.

So with every new barrel, I go through this same process, and the results are always interesting. The bullet likes a certain place in the throat. I can't explain why, I just go with the results. NOTE: I don't change any powder measurements.

I also try different primers to see if they make a difference, and many times they do!

I have a Dasher that likes to be in the lands a pretty good bit using SMK's. I point and trim all my match bullets. I also check the bullet concentricity on every round, if over .002, it goes to the practice box.

Some of my barrels like Bergers (I use VLD and Hybird Bergers), some SMK's, and some Bart's. My 308's are 100% Bergers. The 6mm's like the other bullets.

FWIW, I like .002 neck tension, but if your bullet is jammed, well you better make sure when you chamber it, you are going to fire that round. It could get messy otherwise.

JMO, Dennis (this works for me)
 
If your question is really about jump vs jam in bullet seating, there is one advantage in starting at the jam position. Your pressure will likely not go higher as you proceed with your testing into jump territory.

So I start load development by choosing a moderate charge for the given bullet, and load 3 each starting with .010 into the lands (+.010), then .005 also in, but then jump to .005 OUT of the lands (-.005), -.015, -.025 and further if I think the bullet brand typically prefers more jump.

The reason I don't seat to touch is that minor variations in bullet Ogive and seating can lead to the bullet being slightly in or off the lands and that will make for some variations in pressure and therefor velocity, skewing results.

Once I have determined the best seating depth, I then work on charge wt., then neck tension, then primers.

Loading well off the lands can have some positive results. At seating depths involving large amounts of jump, the bullet will be preceded down the barrel by burning powder and hot gasses coating the barrel with a fresh layer of graphite and, in my thinking, causing the bullet to ride on a cushion of expanding gas from propellant trapped between the bullet and barrel.

I spoke to one shooter at the range who was loading for this 308 using 125 grain bullets, H414, and seating -.180 off. He was getting phenomenal velocity and accuracy for his hunting load.

Velocity and accuracy are not necessarily related, so choose what's best for your application.

FWIW, I find Federal Gold Medal ammo is loaded at about .007 INTO the lands in my SAAMI chambered Shilen select match 308 barrel, no doubt contributing to its intrinsic accuracy.
 
If developing loads for a BR rifle I will work with one of two choices. First, if a VLD type bullet design, .010 in. Second, if a non-VLD type bullet, I go with .010 off. If developing for a hunting or "precision" rifle I always work with off the lands no matter the bullet type.
I find the best load first and then fine tune seating depth when that step is complete.
 
Thanks for the reply, I understand now. I had .308 on my mind and that wouldn't be much of a moderate load. o_O
 
Hengehold said:
I recently received some reloading advice from one of the prominent bullet making companies that we all use. The advice was to begin load development with a moderate powder charge and shoot for groups by adjusting the SEATING DEPTH and leaving the moderate powder charge constant.

For example, shoot 5 shot groups of the following:

.010 jam, 45.0 gr Varget
.005 jump, 45.0 gr Varget
.040 jump, 45.0 Varget
.070 jump, 45.0 Varget

After testing different seating depths, Pick the seating depth that resulted in the best group. The second step is to adjust the powder charge while keeping the seating depth constant.

For example let’s say .040 jump provided best groups in the initial testing of seating depth. Now we will shoot 5 shot groups with the following:

.040 jump, 45.0 Varget
.040 jump, 45.3 Varget
.040jump, 45.6 Varget
.040 jump, 45.9 Varget
Etc.

I have never considered using seating depth as the first step to find the tune of a barrel. I have always done load development the other way around with adjusting the powder charge first and then fine tuning with seating depth.

Question: Does anyone else here prescribe to the “seating depth first” approach to load development?

My background is in NRA high power competition. Maybe this is something that is common among the benchrest community?

Thanks,

-Trevor
Click to expand...
Ah yes
The Berger method
 
I test seating depth/distance to lands with a moderate charge before testing powder charges with all brand bullets.

To add. I fine tune seating depth after OCW has been identified.
 
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In my experience seating depth and powder charge are not completely independent- you can get to suboptimal results if you don’t test all the combinations.

That said, most of the time, picking a reasonable charge weight and powder (moderate or not), and then testing seating depth has worked well for me. Especially when using a tuner to clean up at the end.
 
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