What to tune first: seating depth or powder charge?

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Yosemite Steve

New member
My big question for the moment? Is it more efficient to develop ammo for a particular gun and bullet by starting with seating depth or powder charge. I was advised by someone who is very experience to start with a moderate powder charge and find the best group by adjusting seating depth first. This has worked well for me... but I usually shoot about 30 rounds for that process and then another 30 or so to seek the best charge for the given powder.

Last night I was reading about ladder testing first and then seeking the sweet spot in depth. Since one affects the other where do you start?

Another thing I read about was listening to the rifle or feeling it hit that sweet spot where it gets really accurate. One person described it as a "boing" that happens when the harmonics of the barrel meet the acoustics of the detonation. I have experience this! My rifle has indeed made more of a "boing" on certain loads but I never really thought much of it at the time.

Here is link to one method, by Sierra Bullets Product Development Manager Mark Walker: https://sierrabulletsblog.com/2014/07/03/long-range-load-development/

Also this link from 6.5 guys: http://www.65guys.com/10-round-load-development-ladder-test/

The thing about the ladder test is that there are variables in shooting that might throw this process off. I don't have a fancy bench rest. I use bags and a level. I do have a new chronograph though and that might be my ticket!

Where do you start?
 
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I experiment with bullet first. Powder and powder charge second. And at the bottom of the list id seating depth (distance to lands). FWIW, my stock Ruger 308 bolt gun gives me sub 1" groups consistently with occasional 7/8" groups (best repeated group 3/4") with Hornady bullets seated to Hornady OAL suggestions...
 
Yosemite Steve asked:
Where do you start?
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I pretty much follow a protocol similar to the one described in your 6.5 Guys posting. The difference is that for each candidate charge weight, I load ten rounds. All are loaded to the COL listed in the published data I am using. Five are fired through the chronograph to get a notional idea of the velocity and consistency. The other 5 are shot for accuracy.

I do not shoot from a bench. I always shoot off-hand; often using the sling as a hasty sling to help stabilize the rifle while it is being held. This can, of course, introduce variables beyond powder charge and seating depth, but I test loads under the same conditions they will most likely be used.

After finding the most accurate charge, I will, if necessary, play around with the seating depth of the bullet and test again. But, the seater plug has not been adjusted on my 223 Remington dies since they were first set up in 1979.

Another thing I read about was listening to the rifle or feeling it hit that sweet spot where it gets really accurate. One person described it as a "boing"...
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My hearing is not good enough to hear that so I am pretty much left having to do all my analysis on the basis of data gathered at each test.

I do have a new chronograph though and that might be my ticket!
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I am not aware of a light-sensing chronograph that has a provision for calibration. They are entirely dependent upon the known distance between the sensors remaining the same and the accuracy of the timer chip. The chips are sensitive to voltage and temperature, so always start with a fresh battery.

Even so, recognize the velocity reported by the chronograph will not be the "true" or "actual" velocity. A chronograph can help you know if your rounds are delivering a consistent velocity. In load development, they can also help identify those "nodes" where an increase in powder charge does not result in a significant increase in velocity.
 
On an initial I do a run of 3/10 t0 5/10 power charge increase from minimum to upward of maximum but usually a bit below.

10 rounds each typical.

Bullet searing is .015-.020 off the lands initially or if I have used that bullet and found it has a sweet spot I use that.

When I hit good areas I note that as an area to try.

Then I go back and load 3/10 below, spot on and above (if there was an indicator that the whole thing might need to shift down or up I will do so)

At that point I usually have 15/20/15.

That is the point I will change bullet seating depth.

I have looked at ladder testing, I don't usually have 200 yards to work with and at least for my capability of shooting I don't think its going to tell me anything.

I expect to see two decent areas, one under mid load and one under max load. Sometimes 3.

As I shoot mostly at 100 yards I tend to the lower loads.
 
First, work up the load. Then, if you feel like it, you can fiddle with the off-the-lands thing.
Ladder testing does not tell you anything about a particular load. It only tells you the POI in relation to other loads.
Velocity means diddly if the load is not accurate.
"...start with a moderate powder charge..." You start with the Start load and go up by half a grain to the max load for a given bullet weight and powder. Load 5 or a mag load(hunting rifles usually have a capacity of 4 or 5) of each. Use the Max OAL given in your manual.
"...listening to the rifle or feeling it hit that sweet spot..." That's nonsense.
"...the acoustics of the detonation..." Nothing is more irrelevant to reloading than the sound of the gun shot. No such thing as a detonation of smokeless powder with proper loads either. Smokeless powder does not explode. It burns. Only time there might be a detonation is with below minimum powder charges.
The harmonics of the barrel is about its vibration when a shot is fired. It has nothing whatever to do with the acoustics of the detonation.
 
"...listening to the rifle or feeling it hit that sweet spot..." That's nonsense.
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There are times when I can feel/hear the rifle ring more pronounced than other times. It is discussed here: http://forum.accurateshooter.com/threads/finding-an-accuracy-node.3779618/ Maybe I misused the term "acoustics of detonation" I am referring to the alignment of the combustion shock wave and the ring of the rifle. It makes a "boing" that is more pronounced with certain loads.
 
Ladder testing does not tell you anything about a particular load. It only tells you the POI in relation to other loads.
Velocity means diddly if the load is not accurate.
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Please read about accuracy nodes. I think that, with the proper equipment, ladder testing makes perfect sense in that it can tell you where velocity drops slightly with a small powder increase. It is significant in a rifle's harmonics.
 
At the range today, with my new chronograph... I shot the last three bullets I developed for hunting earlier this year. I was saving them to see if they were as fast as the book suggested they might be. All three shots one holed! This is the first time this has happened for me. https://www.dropbox.com/s/eavdg6m3ec024ke/20180101_193702_resized.jpg?dl=0 Be damned if I didn't feel the rifle ring for all three shots. I didn't notice it shooting any other rounds. I'm having my whiskey to celebrate this success! 50.0 grains of IMR 4064 with a 180 SST seated .005 off the lands. 2631,2635 and 2643 fps. Boing!
 
Yosemite Steve said:
Would you elaborate on your bullet experimentation?
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I research bullet manufacturer's descriptions/spec. on their bullets. I research bullets by what I want the bullet to do and which one will fill my needs. I determine which weight I'll need to produce the results I'm looking for. I'll purchase bullets of my target weight and sometimes one a bit heavier or lighter. I'll start with starting loads from my manual(s) and manufacturer's suggestions of OAL. I'll vary the powder loads a bit and if promising I'll continue, but if not, I'll try a different bullet weight. Occasionally when I reach a reasonable load (bullet and powder combination) I'll try another bullet manufacturer. Once I determine a good load I may vary bullet to lands distances, but I rarely have much if any improvement over manufacturer's recommendations (My Ruger 308 bolt gun will give me sub 1" groups and some 7/8" groups and the smallest repeatable group has been 3/4" using standard Hornady OAL recommendations)...

I enjoy reloading and the whole process from perusing my manuals to recording the results and am in no need of an "instant" best load. What fun would it be to find a load in a manual and the first loads give 1/2" groups at 3oo yards?
 
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It depends on what kind of shooting you're doing.
For long range I find a velocity node first (usually the highest one), and then I play with jump for best groups.
Many BR shooters do it differently, because they're not worried about their load falling apart at long range.

Read any of Bryan Litz's books. He explains the science and statistics of load development far better than anyone else.

Tony Boyer's book, "The book of Rifle Accuracy" explains how to do load development for bug-hole Bench Rest groups. It's not quite the same thing.
 
After reading up on this topic and serious consideration I feel like the bullet seating is a variable that might best be considered first and last. The reason I say this is that bullet seating depth has two major effects on bullet velocity.

First, the initial pressure spike becomes more pronounced the closer the bullet is to the lands which will in turn cause the powder to burn at a different rate which will produce different results with different powders. With any propellant increased pressure=increased burn rate. One particularly good thing about a fast pressure spike at the onset of ignition is that the case will seat itself into the chamber more rapidly. What is potentially bad, however, is that the pressure curve becomes more of a spike when it is most ideal to have a plateau in the pressure so that the bullet may achieve it's velocity more efficiently. This is why Hodgdon's Superformance powder was able to achieve 100-200 fps higher velocities without topping maximum pressure standards. The recoil is amazingly soft for such a high power charge.

The second major effect is the relation that case volume has to combustion pressure. Seating the bullet long decreases pressure because there is more volume inside the case. There has to be a point in seating depth where the pressure spike from seating on or too close to the lands is relieved and the case volume effect is realized.

In seating a bullet .050" deeper I gained 103 fps. The charge was 57 grains of Superformance behind a 180gr. SST. The first group was jammed at 3.375" COL which averaged 2615 fps. (a load I tested to be safe a couple weeks back) After realizing my error in lands measurement I picked up where I left off with my new COL of 3.320" (which is .010" off the lands) and discovered how powerful this powder is. Yesterday I tested apples to oranges and shot the 57 grain load with a COL of 3.320" out of the same exact bullets resized the same and got an average of 2718 fps with a deviation of 3.4! The primers were notably less flat than the previous load.

If a person were to keep seating the bullet deeper it would eventually cause the pressure to spike more. Somewhere in the middle is a place that creates the smallest spike and a more consistent pressure curve. Hodgdon suggested a 3.330 COL without specifying a specific bullet other than 180 gr. 3.330 happens to be right on my lands so I seated .010" deeper.

So that leaves me with the conclusion that seating depth and powder charge are both fluid and codependent on results. The chronograph is the ultimate weapon here because it tells where the velocity nodes are. Once we know the node for a given bullet weight we can find the harmony between COL and charge weight. My plan is to set up a portable loading table and take it to the range so I can adjust the seating depth some, test it on the chronograph and then adjust the powder charge until I find the smallest charge that creates the node velocity.

This is all very hypothetical but I have put a great deal of thought into it. Some references I have are:
Jeff Cooper's article http://www.frfrogspad.com/loaddev.htm
Ron Dague at Sinclair International https://www.sinclairintl.com/guntech/the-importance-of-bullet-seating-depth/detail.htm?lid=16085
Bryan Litz http://www.bergerbullets.com/wp-content/uploads/2013/03/COAL.pdf
 
For a change i agree almost completely with T.O'heir.
Only difference is i increase by 0.3 gr.

Powder charge gives you velocity change greater than changes in seating depth in most ( not all) bottle necked rifle cartridges. I look for the 3 closest shots vertically. Powder charge is the middle one. So your looking at 0.6 gr difference.

Then play with seating. Your groups should ( unless your using VLD) tigjten up, then reach a point where they start to open up.
 
Then, if you feel like it, you can fiddle with the off-the-lands thing.
Ladder testing does not tell you anything about a particular load. It only tells you the POI in relation to other loads.


How can anyone take that seriously...
 
I read that one too. His method is different than most in that he keeps jamming deeper. I suppose it may depend on the gun but I am trying to avoid jamming (for the moment). I did have some good accuracy with jamming a while back but I was getting primers flowing into the pocket bevels at mid range loads so I stopped doing that. If I were going to do bench rest shooting I would probably go back to that though because I had some groups with 165 grain bullets that were all touching at 100 yds. The other problem was that the bullets were only in the brass about 1/8 inch.
 
I would take the ladder test seriously if I had equipment like the author had. I'm shooting of a bag with a 30 and 75 year old guns. The ladder test tells you where your velocity nodes are.
 
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With a new rifle to load for I always start by choosing the bullet, based primarily on terminal performance (game or target specific), and secondarily on BC, depending on the range at which I expect to shoot. I may have a second bullet in mind, but will only work with one at a time until I achieve my goals or scrap it.

Second is powder selection. I pick two, usually the one that shows the highest max velocity in the books (often a compressed load of slower powder), and the one that has closest to 100% loading density at max.

Third is seating depth. I start at 0.010" off the lands and won't seat closer, as long as it will cycle through my magazine. With this bullet jump, when I reach a maximum charge in my rifle, then any subsequent seating depth increases will reduce, not increase, the pressure.

Fourth is finding the max charge. I load three of each load, in half grain increments, unless the case capacity is under about 40 gr of water; then I drop to 0.3 grains. I shoot these for groups and over a chronograph, checking and measuring for case head expansion and pressure signs.

My goal is to find the most accurate load at the highest velocity. If the accuracy is good, as long as the velocity is reasonably close to max, then great. If accuracy is poor, I'll try the second powder and/or another bullet. The last thing I do is play with the seating depth to try and fine tune an already accurate load. I'll load 5 each in increasing 0.010" increments, up to 0.050" off the lands.
 
I have never messed with adjusting seating depth. The round will either fit the rifle or it won't. I normally choose med to heavy bullet weight's for caliber and a med burning on the slower side powder. Once I have the bullet seated just off the lands, whatever that may be, I adjust powder charges in .5 gr increment's. Over the year's I have had a number of rifle's that if I do my job, they'll shoot 1/2" group's. I have 4 of them right now. But the most critical part of the load is the shooter! The next most critical part is rifle bedding. I have two rifle's I have not bedded, Patriot that I haven't figured out how to yet that is a half inch shooter if I do my part. The other is a mod 70 feather weight in 6.5x55 that stay's at and just under 1". Had it out the other day with some 129gr Hornady loads that went just under an inch and 140gr Hornady's that went right at 1/2". Normal for this rifle has been just under an inch. Come to think of it, my 6.5x06 is scary accurate with 129gr Hornady's and better with 140gr SMK's. None, as I said have had seating depth adjusted. Been that way for close to 50 yrs for me and I see no need for a rifle that shoot's even 3/4" for hunting and hunting is mostly what I do.
 
Black mamba. Unless you are on the rifling. Seating the bullet deeper into the case will always increase pressure. Less volume = more pressure. Increasing COL will reduce pressure until you hit the rifling.
 
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