Seating depth - does it even matter?

[solarshooter]

I disagree. If my goal is sub-MOA for 10 shots and the first 3 are 1.5", that doesn't fit my criteria and based on the testing I've done and the subject at hand, no amount of tweaking seating depth or likely changing powder charge without sacrificing an unwilling amount of velocity will make that load consistently sub-MOA. So I change a component, and start over.

In this example, which I think is pretty extreme, I guess you are right. What I was saying is if the first 3 shot group is 1.5", and another hypothetical variation, let's say different seating depth, grouped 1" for 3 shots, you wouldn't really be able to say that group was better, worse, or different at all than the first.

 

[Harvey_NW]

In this situation, I would keep shooting because I want to establish “the best I can do with this combination.” Because the shooter is always the largest source of error. Unless you are eliminating shooter error and environmental factors, I think it still makes sense to finish the test.

My main objective with "load development" is to get to my goal with the least amount of components burnt up as possible, so if the group exceeds 1 MOA at any point before I reach 10, the rest get pulled. Once I find a combination that meets my goal, I'll track it and repeat it over time. If I can't get to my goal using combinations of 2 different temp stable powders, and 2 or 3 high BC bullets, that barrel gets tomato staked because I don't trust it to do what I expect it to.

In this example, which I think is pretty extreme, I guess you are right. What I was saying is if the first 3 shot group is 1.5", and another hypothetical variation, let's say different seating depth, grouped 1" for 3 shots, you wouldn't really be able to say that group was better, worse, or different at all than the first.

I 100% agree with that.

 

[Q_Sertorius]

To be clear, I'm not saying anything about your shooting abilities or implying any offense. I'm talking purely about demonstrated precision on target as you change certain variables in your load.

I think it's very unlikely that your gun is shooting ONLY 0.5" 5 shot groups, never worse. Again, I'm saying ALL groups for a given load, not excluding any flyers or shots. And I think if you increase that shot count to at least 10, you will see larger and more consistent group size numbers. And you might see less sensitivity to seating depth than you originally stated. Your case would be by far the most sensitive/extreme reaction to a seating depth change that I've ever seen or heard of.

And it is POSSIBLE that you are seeing a real signal. But based on the evidence you provided, I don't think you've PROVEN that yet.

Here's 15 10-shot groups I just shot this weekend with my T1X. Top 2 rows are testing different lots of ammo, bottom row is same lot as top row, but with my suppressor added. You can see how different the 10 shot groups can be, both in size, shape, and shot distribution within the group. Imagine how much more extreme that would be with only 5 shot groups.
View attachment 895226

When I am developing a load, I want to know what groups of the same size look like.

I will use your bottom middle target as an example.


Let's assume that the "flyer" and the top and bottom corners were the first three shots and that was a 1.5" group at 100 yards. I would like to know that the next seven ended up between the two closer shots. I would not discard the "flyer", but I think the load might need further testing (another 10-shot string). Because that might indicate a loading process error or shooting error on my part. If the next 9 10-shot groups all looked like the smallest groups on this page, I would be pretty happy with my process and my shooting.

 

[solarshooter]

My main objective with "load development" is to get to my goal with the least amount of components burnt up as possible, so if the group exceeds 1 MOA at any point before I reach 10, the rest get pulled. Once I find a combination that meets my goal, I'll track it and repeat it over time. If I can't get to my goal using combinations of 2 different temp stable powders, and 2 or 3 high BC bullets, that barrel gets tomato staked because I don't trust it to do what I expect it to.


I 100% agree with that.

I think/operate similarly, except I'm using Mean Radius rather than group extreme size. Could argue it's more lenient in some ways since it allows for extreme outliers, but as I've shown thoroughly here I think it's far more insightful in the end.

 

[TaperPin]

But more rounds can reduce the Mean Radius. This is why it's such a better/more powerful metric, you are getting information from all shots in the group rather than just the extreme-most two.

Which group is more precise (imagine they have the same extreme size, despite my shitty artwork)?
View attachment 895200

I’m not saying your mean radius is a bad metric for everyone, if someone likes the information it provides then good, but it’s not a metric I care for. Target shooters that win or lose based on 8s, 9s, 10s, and Xs benefit from groups with a lower mean radius. Even competitions shooting plates with hit rates below 100% benefit from it. My shooting style while big game hunting is to only take the shot if it’s a sure thing given my ability in that position and range, so the distribution within the group doesn’t change the outcome. I’d feel the same way if 9 shots went in the same hole and the tenth opened the group. During practice the ability to hit 10 out of 10 plates at max range is the goal. In the field hunting life isn’t perfect, so hits are more like 95%, but I’ve never felt a better mean radius would be beneficial.

This goes against what Brian Litz thinks is the ideal answer in his simulations, but the assumptions in his models are much more loosey goosey as to shooter ability, rifle accuracy and other inputs. As soon as he starts talking about “average hunter” this or that, and their first round hit percentages as the basis for the simulation inputs I lose interest.

 

[JGRaider]

I find powder charge by taking max charge minus 2g and going up in .5g increments. I keep adding .5g until i see pressure. Then I pick the biggest charge that produced an acceptable consistency of grouping but not showing pressure. In initial load development I set seating dept to mimic factory ammo that shot consistenly well. Once i got my powder charge i did 10 rounds of .025 and 10 of .05 longer. Groups went from 1/2" to over 1" then 2.25" with those jump changes

You realize that extending OAL closer to lands increases pressure, right? I'm just the opposite.....close the lands, find pressure, go from there, not the opposite.

 

[Q_Sertorius]

My main objective with "load development" is to get to my goal with the least amount of components burnt up as possible, so if the group exceeds 1 MOA at any point before I reach 10, the rest get pulled. Once I find a combination that meets my goal, I'll track it and repeat it over time. If I can't get to my goal using combinations of 2 different temp stable powders, and 2 or 3 high BC bullets, that barrel gets tomato staked because I don't trust it to do what I expect it to.


I 100% agree with that.

I understand your objective of "get to my goal with the least amount of components burnt up as possible" and I am not arguing with it. I used to do that as well. But now I think it is a false economy, because the three shots I fired have no statistical value whatsoever. It is too small a sample size to compare with anything else or to base any decision on. The information gained from the rest of the string is still valuable and worth pursuing.

I accept that I am the greatest source of error, both in the loading process and in the shooting process. Shooting, even with "subpar ammo", is still a test of how I am shooting on a given day with that combination of factors. That means that I want to finish the test even if it looks like I "flunked" in the first three shots. Because as much as we might like to think that we are testing the rifle, we are really testing our ability with that rifle.

Apart from bringing in another shooter (and even that is just introducing another uncertain element to the equation), it's the only way to really tell whether the error is with me, or with the rifle. Obviously, if I bring in a better shooter and he shoots a .25 MOA 20-shot group with the rifle, while I shoot 1.5 MOA 20-shot groups, that tells me something more about myself.

And now that I have a Garmin, I have another way to test my reloading process, as long as I record full and complete data. If I shoot the 10-shot string, call my shots and record that in my logbook, then compare my call with the actual outcome, and pair them up with the velocity, it might be that I can determine that the "flyer" was 50 FPS slower than the rest of the group. Again, I cannot exclude that "flyer" - it is still representative of what is really being tested - but I can try to see if there is a process improvement I need to make in loading.

 

[Harvey_NW]

I understand your objective of "get to my goal with the least amount of components burnt up as possible" and I am not arguing with it. I used to do that as well. But now I think it is a false economy, because the three shots I fired have no statistical value whatsoever. It is too small a sample size to compare with anything else or to base any decision on. The information gained from the rest of the string is still valuable and worth pursuing.

For me it comes down to wasting money by burning up valuable components and barrel life, if I'm going to practice I want it to be as identical to real hunting situations as possible, with the tools I'll be using. 3 shots outside of my criteria has enough value to tell me 3 things; the odds of those first 3 being the extreme outliers of the cone of fire are slim to none and they happened regardless, that group could more than double in size, and typically groups grow with sample size. There is no value to me in continuing.

I accept that I am the greatest source of error, both in the loading process and in the shooting process. Shooting, even with "subpar ammo", is still a test of how I am shooting on a given day with that combination of factors. That means that I want to finish the test even if it looks like I "flunked" in the first three shots. Because as much as we might like to think that we are testing the rifle, we are really testing our ability with that rifle.

I agree with this, but I've spent countless hours learning, shooting, and testing to know if I broke off 3 clean shots or not. If it's a new rifle with new components I might be a bit more lenient toward the results and continue testing a bit further to validate a conclusion or diagnose an equipment failure. But since I drank the "Rokslide Kool-Aid" and use quality equipment and components recommended ad nauseum here, I haven't had to deal with that for quite a while.

 

[pbroski]

Lot's more variables are introduced at 670yds than seating depth, IME.

I started by shooting 1 on the left, then 1 on the right, then back to left, then back right. Back and fort like this until the test was done. The variables would be evened out to the point of not being a factor, I would think. Apples to apples comparison.

 

[pbroski]

Man, that's some dedicated testing! I can definitely appreciate the amount of work put into this, but as mentioned above there are a lot of variables introduced when shooting a 22 cal 657 yards with sticks and a pack leaned up against an ATV. Regardless, I appreciate the input. Good shooting!

Thanks!

The variables are evened out by the test method (shooting round robin). Hard to imagine that variables are effecting one group more than the other, with 60 rounds fired. Not to mention the 10 round groups also being in line with the 30 round groups.

 

[pbroski]

Yeah, there's a reason testing is typically done at short range. Environmental effects will add significant dispersion to your groups at longer ranges, especially over a 60rd course of fire. You also have barrel heat, and shooter fatigue to consider.

Now, 30rd groups are certainly more statistically robust and useful for distinguishing small differences, but they need to be 30 "perfect" shots, as in no other variables changing during the courses of fire. Very hard to achieve that level of consistency without machines and indoor ranges, which is why that type of testing is usually done with machines and indoor ranges!

Once again I'll advocate for using shot radius, mean shot radius, and the T-test to more rigorously assess different samples. This post has an example of how I do this: https://rokslide.com/forums/threads/what-did-you-do-in-the-reloading-room-today.338563/post-4125326.

You'll note in that test I did not see any significant effect from seating depth, and I made a very drastic change with a secant ogive bullet.

I do think that seating depth can matter for loose chambers with long freebore, where the bullet is jumping truly unsupported for a significant distance before engaging the lands and can develop yaw before engraving which will manifest as increased dispersion on target. For instance, a SAAMI 308 chamber has a 0.310" freebore, meaning there is 0.001" clearance around the bullet on all sides. Compare this to a 6.5CM SAAMI chamber with a 0.2645" freebore, or 0.00025" clearance around the bullet on all sides, effectively a light interference fit. This will constrain the bullet much more tightly and prevent it from developing any appreciable yaw even with a very long jump. So you might find different results testing in different chambers with different bullets and jumps.

The point I tried to show was that small changes are where the big gains are.

 

[pbroski]

, like a 10x scope, shooting sticks,
Atv tire pressure and the pack. Not to mention the environmentals

Think again. You don't put 30 rounds under 1 moa at 657 yards by being lucky.

 

[JGRaider]

I started by shooting 1 on the left, then 1 on the right, then back to left, then back right. Back and fort like this until the test was done. The variables would be evened out to the point of not being a factor, I would think. Apples to apples comparison.

Doesn't matter to me really, but that has nothing to do with atmospherics, mirage, wind, parallax, shooter error, etc. I'm assuming there were no wind flags used either?

 

[Mikido]

TLDR

For hunting, not one bit.

 

[wind gypsy]

You realize that extending OAL closer to lands increases pressure, right? I'm just the opposite.....close the lands, find pressure, go from there, not the opposite.

Not necessarily. If a guy is 0.225" off the lands, its possible that seating the bullets out another .030" reduces pressure.

I've posted this graph a handful of times and I assume that the distance at which pressure is lowest changes based on on chamber, powder, powder charge, and bullet.

 

[ddowning]

, like a 10x scope, shooting sticks,
Atv tire pressure and the pack. Not to mention the environmentals

I used to think you needed high mag to shoot tight groups. Years ago, I did load development for a friend's rr ar. It had a red dot with a 3x magnifier. The dot was 4 moa. I drew a 4" square to put the 4" dot in at 100 yards and proceeded to shoot multiple sub 1 moa 5 shot groups, some under 1/2" quickly busting the myth that high mag is required for tight groups. If you can see well enough to quarter the target you are good for all but the most hair splitting of circumstances. The above was years before people started talking about the pitfalls of additional load development.

 

[Dobeman887]

I have been reloading for many years, but have just now begun to "chase the lands". As one would expect, magazine length is something that greatly impacts the maximum COL. Unless I am single feeding the shots I can only seat that bullet so close to the lands. I haven't gotten to try out any of my new rounds yet (been too blistering hot here in N IL the past week). I have made rounds for my Rem 270 and Franchi 350 Legend. Will hopefully test soon with 10 shot groups, allowing barrel to cool after 3-4 shots. I have no idea what I will find, but I am curious.

 

[Harvey_NW]

I have been reloading for many years, but have just now begun to "chase the lands". As one would expect, magazine length is something that greatly impacts the maximum COL. Unless I am single feeding the shots I can only seat that bullet so close to the lands. I haven't gotten to try out any of my new rounds yet (been too blistering hot here in N IL the past week). I have made rounds for my Rem 270 and Franchi 350 Legend. Will hopefully test soon with 10 shot groups, allowing barrel to cool after 3-4 shots. I have no idea what I will find, but I am curious.

Chasing the lands is for the birds, load to a functional mag length and test it there. If it doesn't shoot, swap a component. I hope this goes well for you because once it clicks, it really makes "load development" so much more simple, efficient, and enjoyable. Tinkering was fun in the beginning while learning, now I want to be shooting targets at distance asap. Good luck!!

 

[Dobeman887]

Chasing the lands is for the birds, load to a functional mag length and test it there. If it doesn't shoot, swap a component. I hope this goes well for you because once it clicks, it really makes "load development" so much more simple, efficient, and enjoyable. Tinkering was fun in the beginning while learning, now I want to be shooting targets at distance asap. Good luck!!

I have certainly read this. Will try it with a couple of rifles and see what happens. As I mentioned magazine length is a constraint, so in reality that is far as I will be able to go. It will either increase accuracy or it won't. I will report back on my findings- hoping to shoot a bit this week, but the heat looks like it is going to continue here in the upper Midwest.

 

[ddowning]

I have been reloading for many years, but have just now begun to "chase the lands". As one would expect, magazine length is something that greatly impacts the maximum COL. Unless I am single feeding the shots I can only seat that bullet so close to the lands. I haven't gotten to try out any of my new rounds yet (been too blistering hot here in N IL the past week). I have made rounds for my Rem 270 and Franchi 350 Legend. Will hopefully test soon with 10 shot groups, allowing barrel to cool after 3-4 shots. I have no idea what I will find, but I am curious.

I will try to be the second voice of reason. I tried chasing the lands when long range shooting was much less popular and knowledge was not as readily available. I did it for 2 barrels. It made accuracy WORSE, as the powder charge needed to be changed to bring it back.

Sometimes I throw the barrel away after the initial load stops shooting. If it is a screamer barrel, or I am being cheap, I can usually get more rounds out of it by moving the bullet out and adding powder. This is after 100s or 1000s of rounds though. Also, it is with chasing sub 1/2 moa for 10 rounds. I have never owned a hunting rifle/caliber that would consistently put nearly all 10 round groups under 1/2 moa. For very good 3/4 - 1 moa rifles it is not very easy to see. For good to average 1.25 moa to 2 moa rifles it is very difficult to see a difference. This is with 10 shot groups or more. Shooting less than 10 shots will definitely lie to you. 10 shots will occasionally, but I rarely shoot more as I feel it is "good enough."

TLDR version, only do it if you love to experiment and prove things to yourself. Chasing the lands is not beneficial to accuracy. It is detrimental.