Does seating depth really matter?

[F Class John]

Tagging onto what @Tod Hendricks posted last week regarding his experiences with seating depth and Berger hybrid 180s I thought I'd do a simple but effective demonstration. I used a known load (my left overs from SWN last week) and covered .100" in seating depth over 20 shots while shooting my 600yd match last night. Enjoy

 

[Bill Norris]

I think what we are seeing here is the seating depth may not matter as much at longer distances but maybe it does matter more at shorter distances.

 

[fkimble@charter.net]

Hmmm? If any thing Bill, I would think it was the other way around! Not disagreeing but things usually go south the further out you go?
PS: did not watch video

Frank

 

[Ahhnother8]

What is the velocity (muzzle/terminal) of each individual round? With that terminal ES, one would expect significant elevation issues at 1000 yards.

 

[F Class John]

What is the velocity (muzzle/terminal) of each individual round? With that terminal ES, one would expect significant elevation issues at 1000 yards.

I didn't have my chrono with me last night but the SD at target for all 20 shots was only 11.2

I will definitely repeat the test next time I'm at my 1000yd range (different club and different schedule).

 

[Bill Norris]

Hmmm? If any thing Bill, I would think it was the other way around! Not disagreeing but things usually go south the further out you go?
PS: did not watch video

Frank

Absolutely, normally the groups tend to grow in size at longer distances but maybe this is something that has been over-looked. My reason for saying that is normally at 100 yds. when seating depth is tested you will see groups open up and close up. Would be interesting to see this group of 20 shots tested at 100 yds.

 

[JFrank]

I think what we are seeing here is the seating depth may not matter as much at longer distances but maybe it does matter more at shorter distances.

Not to speak for @F Class John but what I’m seeing is a one shot per increment depth test that imo shows tendencies just as a horizontal sine wave foremat would, or a tuner test foremat just with less shots and one point of aim.
I do a similar style with increased shots as my experience level isn’t quite up to John and Tod’s I require a bit more data. ( nice shooting John )
Jim

 

[Ned Ludd]

I think the key result of this test is that you have a rifle/bullet/powder/primer combination that shoots really well. Thus, altering seating depth within the stated range did not cause a shot to fall outside the 10-ring. However, you did not shoot an additional 20-shot target where all the rounds were seated at a single "optimal" seating depth test for comparison. I suspect if you had, you might find the ES in terms of distance from center for both groups were similar, but the SD for distance from center was smaller for the group fired with ammunition loaded at an optimal seating depth. In other words, over time the single optimized seating depth load would likely produce the better scores.

As we know, the more shots one fires in a group, the larger that group will generally be until the theoretical maximum group size of the setup is reached. I believe that largely represents total accumulated error, which is something we can minimize or even eliminate when shooting a seating depth test consisting of only 3 to 5 shots per group at a relatively short distance. But that does not mean that what we observe during such a seating depth test isn't real or meaningful because the sample size is too small. Rather, it means that the observed change in group size as the number of shots gets larger is because additional sources of error accumulate to the extent that seating depth is no longer the limiting source of error. Thus, the effect of seating depth may become more difficult to visualize as group size increases. Along that line of thinking, is it safe for us to assume you will continue to do seating depth tests and load your match ammunition to a single apparent seating depth optimum, rather than just seating bullets to within a .100" seating depth range?

 

[Onebad06VTX]

YES it does!
VERY MUCH SO!!!!!!!!!!!!!

 

[gunsandgunsmithing]

Not to speak for @F Class John but what I’m seeing is a one shot per increment depth test that imo shows tendencies just as a horizontal sine wave foremat would, or a tuner test foremat just with less shots and one point of aim.
I do a similar style with increased shots as my experience level isn’t quite up to John and Tod’s I require a bit more data.
Jim

Same here. Whenever I see a test like this my eye starts looking for tendencies or patterns where it repeats. Looks like something repeats about 7 numbers apart, or .035" seating depth change but it's not perfect and hard to say with only one shot groups. Not enough info to form much of a conclusion, for me.

 

[F Class John]

More than anything this particular test was to show in a simple way that even across .100" variance, the group never opened up much more than about .75moa which I think is drastically different than most people's expectations.

I think everyone still agrees seating depth matters, and is in fact necessary to optimally tune a load, but like Tod https://forum.accurateshooter.com/threads/seating-depth-doesnt-matter.4088405/, Short Action Customs/PRB https://shortactioncustoms.com/bullet-jump-research/ and others have shown in past testing, it's not as critical as other aspects of load development such as your powder charge and the accurate nodes for seating may in fact be much wider and safer at certain depths than previously believed.

 

[jackieschmidt]

I suppose this test is intended for FClass and Precision Rifle shooters.

In my 30BR VFS Rifle, .005 either way of my optimum seating depth is the difference between a sub .200 agging capability and a .250+ agging capability.

My 6PPC Group Rifle is a little more forgiving, but not much.

 

[Jefferson]

I thought at 1000 yards the seating depth test at one thou or 2 thou intervals was the last of the tuning we do to determine what we will take to the line in the registered shoot on the weekend

testing the day or 2 beforehand at the range we will be shooting at

just sayin

 

[RegionRat]

I found the SD of 11 as measured by the SM interesting.

Knowing that every large seating sweep I have ever run shows a trend in velocity, that was a pretty forgiving SD considering the size of the seating depth sweep.

 

[F Class John]

I found the SD of 11 as measured by the SM interesting.

Knowing that every large seating sweep I have ever run shows a trend in velocity, that was a pretty forgiving SD considering the size of the seating depth sweep.

I've done lots of seating tests in the past and almost no measurable difference in velocity compared to a single seating depth test and its velocities. In fact I did one last year that I remember where I shot close to 50 rounds (all same powder charge) but a wide range of seating depths and my ES was something like 19 across all the shots. That's more than acceptable for me and what I'm looking for so I don't really worry about seating depth in terms of altering my velocities much if any.

 

[gunsandgunsmithing]

More than anything this particular test was to show in a simple way that even across .100" variance, the group never opened up much more than about .75moa which I think is drastically different than most people's expectations.

I think everyone still agrees seating depth matters, and is in fact necessary to optimally tune a load, but like Tod https://forum.accurateshooter.com/threads/seating-depth-doesnt-matter.4088405/, Short Action Customs/PRB https://shortactioncustoms.com/bullet-jump-research/ and others have shown in past testing, it's not as critical as other aspects of load development such as your powder charge and the accurate nodes for seating may in fact be much wider and safer at certain depths than previously believed.

I suppose that's true if .75moa is acceptable for whatever discipline. What I see is the test shows how bad it can shoot and maybe, how good. Clearly, it matters to accuracy and even in your test, that seems clear. I guess it depends on your accuracy needs. But no, in no way do I see that test as saying seating depth doesn't matter. You're simply between as good as it can be and as bad as it can be. If you're ok with its worst, then yes...seating depth doesn't matter to you, in that scenario. It's important to know what it looks like when your gun is completely out of tune, when it's completely IN tune and everywhere in between, which naturally also shows how far it is between the two, in terms of powder chage, seating depth or tuner travel. These are certainly all of value.

 

[gunsandgunsmithing]

I've done lots of seating tests in the past and almost no measurable difference in velocity compared to a single seating depth test and its velocities. In fact I did one last year that I remember where I shot close to 50 rounds (all same powder charge) but a wide range of seating depths and my ES was something like 19 across all the shots. That's more than acceptable for me and what I'm looking for so I don't really worry about seating depth in terms of altering my velocities much if any.

That test showed 46fps ES, which I can pretty much gurantee is enough to affect tune and the target shows it. Velocity is one aspect but exit timing is related but not linear. Maybe I'm not saying that right but hopefully you know what I mean. Maybe the end meets with your means but we're on a whole different level and speaking different languages if you don't value the change your target shows.

 

[gunsandgunsmithing]

That is what I came away with. If the margin of error/variation is acceptable, then it doesn't matter.

Maybe the answer is to weigh out the difference in tune vs velocity and how they play out on target. A shorter bbl is stiffer and will show less muzzle deflection on target. IOW, they don't shoot as big when completely out of tune. Then we can talk about optimizing gun balance and handling..and optimize the system.

 

[RegionRat]

I've done lots of seating tests in the past and almost no measurable difference in velocity compared to a single seating depth test and its velocities. In fact I did one last year that I remember where I shot close to 50 rounds (all same powder charge) but a wide range of seating depths and my ES was something like 19 across all the shots. That's more than acceptable for me and what I'm looking for so I don't really worry about seating depth in terms of altering my velocities much if any.

It sure looks very forgiving in both group and velocity stats.

I don't get the same when using Varget. It seems to trend down as I go from touch to 80 deep. I have a plot somewhere, I'll add it here if I can find it.

Found it. I get a drop of about 2982 to 2950 for an 80 mil sweep. Still very forgiving is the main point.



ETA: John, I just realized I never looked at the stats on the above tests. It turns out, after running three sweeps of those depths for a total of 51 shots, the SD was all of 12.9 for all of them, and typically 11.3 - 11.5 for any single sweep.

 

[Ahhnother8]

I didn't have my chrono with me last night but the SD at target for all 20 shots was only 11.2

I will definitely repeat the test next time I'm at my 1000yd range (different club and different schedule).

Would you mind taking the time and stepping through each shot and noting the terminal velocity for us? There sure does not appear to be any correlation of seating depth to elevation on target. Am mostly looking at ES, not SD.