Seating Depth Test

[akinswi]

So I decided to try some AA2520 for 30-06 in my M1

I settled on 46.0 grains, Im using CCI No 34 primer. Bullet is Hornady 155gr HPBT

My seating Depths were

3.330
3.320
3.310
3.300
3.290

In attached image, best accuracy came at 3.320 and 3.310 I shot 10 shot groups instead of 5

would my next step be to narrow the seating depths in .003 increments between 3.320 and 3.310

the group at at 3.320 I had 5 shots almost in same hole. The lighting wasnt great so my tiny black dot at 50yds was getting difficult too see

[jetinteriorguy]

I’d go to 3.315, this gives you a +-.005 leeway for variances in seating depth to allow for any ‘slop’ in the machinery/components. This is a nice sized window, in my method anytime I can find a window of +-.003 I’m happy.

[Bart B.]

I suggest you shoot at least 20 shots per test group. 5 are not statistically significant.

[akinswi]

Bart these were 10 shot test groups, I will try 20 tho on the next seating depth test

[Unclenick]

That's a more reasonable number. A lot of folks online go a few thousandths at a time and wind up with small group size differences in one group or another that are not statistically distinguishable from the result of random luck. Scott Satterly is shooting a whole eighth of an inch back from contact with the throat. Berger has pointed out that for VLDs, steps should be 0.030" to 0.040". Anyway, start coarse and then refine.

[Metal god]

Am I to assume the 20+ shot group should be shot in at least two steps if not four . First I do don't think I could concentrate to the level required to shoot a straight through 20 shot group . Second 20 rounds relatively quick through my barrel would result in the barrel getting hotter then I'd want . Third I don't think I'd ever need to know what my SD of a 20rd group would be . Over the years I've seen this adequate group size grow . A lot of shooters like to shoot 3 but many believe 5 is good . Then 10 started being said as the good enough number and I guess now we are at 20 ? How many of us "really" are shooting 20rd groups during load development ? I just rebarreled a rifle and there is zero chance I'm going to shoot 120 rounds to test the first 6 powder charges then another 100 rounds to test seating depth especially at the current component prices . Yes I completely agree more shots means more likely to have the correct analysis but is it worth burning through your $500 barrel faster then need be ? IMHO 5 shot test is good to narrow the charge then a couple 10's to confirm is more then adequate .

[Unclenick]

What has caused "adequate" groups to grow is just how certain people want to be that the groups they see on paper are really representative of what they are likely to get in the future. From the graph below, you can see the horizontal green line that is the average group size. Across the bottom is the number of shots in each group. Then you see the upper and lower lines that show where the likely 95% confidence limits are for future groups of that shot count.

[Metal god]

That may be a nice graph but I don’t agree even a little bit . I hear many talk about all these variables stacking up , canceling out or maybe dumb luck causing group sizes . What I rarely hear is the other types of variables like skill of shooter , quality of firearm , attention to detail as the reloader . A really good marksman with great reloading skills and equipment shooting a great rifle does not need 20 , 30 , 40 rounds to tell them what to expect from there load .

I talk to competition shooters at the range that refuse to do a 10 , 20 shot string through a chronograph . They tell me they are not wasting barrel life for something 1 or 2 shots is going to tell them . Same goes for groups . They know there rifle , components and abilities and don’t need to do 20 shot strings to know if the rifle/load can shoot .

Again I don’t disagree you will get better statistical data the more shots you fire but…….

[akinswi]

Metal god,

It took all my concentration to focus on the 10 shot groups, I had to actually tape up the lense on my saftey glasses to relieve the eye strain from closing my right eye during the strings, I tried to make the dot as small as possible to remove as much human error as I could the eye strain was pretty bad especially in the crappy lightning conditions I had. so I may not attempt 20 shot group Bart B suggested.

I may just shoot 5 , 10 shot groups between 3.310 and 3.20 and pick the best 1 then shoot for a score at SR1 target at 100 yards and go fron there.

This new criterion barrel has exactly 268 shots thru it, so just over 90% barrel life is still left. I think 3000 rds is about the life of them before you start losing some accuracy.

The Barrel seem to run cooler using AA2520 vs 4895, but I typically let the barrel cool some while I check the target and look for the brass in grass

[Metal god]

That’s the brand I just rebarreled a Savage action with (308 Win) . My first one , it only has 70rds down the pipe . I had to reset the headspace because I used a Hanson gauge which is longer then my Forster gauges . Cases were coming out .003 longer then I wanted . I still need to bed the action on the new stock . I’m hoping to get into the 3’s which will be really good for my type of shooting . So far it’s shooting pretty good , time will tell if It’s what I hope it to be .

[taylorce1]

I use the Berger seating depth test for a lot of my loading. It has a much bigger jump, I jump by .040 between bullet seating depths. Starting with .010 off lands or what feeds through the magazine reliably as my starting point. It has worked well for me. Pair it with the "Saterlee" method of finding an accurate load, it has significantly reduced the amount of components I use in load development.

Originally Posted by Berger

Load 24 rounds at the following COAL if you are a hunter (pulling a bullet out of the case with your rifling while in the field can be a hunt ending event which must be avoided) or a competition shooter who worries about pulling a bullet during a match:

1. .010 off the lands (jump) 6 rounds
2. .050 off the lands (jump) 6 rounds
3. .090 off the lands (jump) 6 rounds
4. .130 off the lands (jump) 6 rounds

Shoot 2 (separate) 3 shot groups in fair conditions to see how they group. The remarkable reality of this test is that one of these 4 COALs will outperform the other three by a considerable margin. Once you know which one of these 4 COAL shoots best then you can tweak the COAL +/- .002 or .005. Taking the time to set this test up will pay off when you find that your rifle is capable of shooting the VLD bullets very well (even at 100 yards).

[akinswi]

what is time consuming is sorting the bullets by OAL for the seating depths. I typically sort by ogive but i noticed most ogives were +-.002 so its easier to sort by the OAL when I sort them for the test, If Im shooting 50, I have to have all the same length.

I trimmed my cases to 2.478 instead of my typical 2.484 since the next time I resize will be using a RCBS X die to hopefully eliminate trimming. I will re run the test again with the best node to make sure the trim length doesn’t mess up the barrel harmonics. I dont know if .006 less neck length will make a noticeable diff

[Metal god]

I have found that bullet OAL is almost always worse then base to ogive . Example 77gr SMK's have an oal ES of .007+ but there base to ogive rare is more then .002 . That said your COAL is irrelevant when it comes to advanced reloading IMHO . The real number to have the most consistent jump is case shoulder to seated bullet ogive and that take a specialty tool most don't have . I believe Uncle Nick can point us in the direction of where to get one . Reason "that" measurement matters in when the firing pin pushes the case forward it stops on the chambers shoulder or wherever the cartridge headspaces .

The case base to bullet tip will not give you a consistent jump to lands distance . The next best spot to measure is case base to seated bullet ogive which will get you a pretty consistent jump if you size your cases very consistent case base to shoulder datum .

The next issue is where does your seating stem contact the bullet . There are two possible places I want it to touch . Either right at the junction of the ogive and full diameter of the bullet or exactly where my comparator contacts the bullet . The problem with that is most if not all seating die do not contact the bullet that low .

EXAMPLE : here is three different contact points on a 175gr TMK

Top line is where my Redding comp seating die contacts the bullet when seating .
Middle line is where my Hornady comparator contacts the bullet .
Bottom line is where my Sinclair comparator contacts the bullet .



The point here is that it's very unlikely the base to seating stem measurement will be as consistent as my base to Sinclair comparator measurement is . IMO with out the that shoulder to bullet ogive measuring tool . Your next best thing to do to get the most consistent jump is to measure each individual cartridge base to seated comparator ogive measurement . Adjusting the seating die accordingly for each individual cartridge .

The question one might ask is . Is that small couple thousandths variance from cartridge to cartridge really going to be noticeable on paper if you're jump is .040+ . I'd say not likely much and is why I just seat 5 to 10 bullets and if there case base to my Sinclair comparator are all with in +/- .0015 ( .003 ES ) I'm gtg . That might be a different story if your COAL is at the lands because not that same variance is now giving you pushed into the lands and just off the lands from cartridge to cartridge . I've found to just be touching the land to give me my worst groups . I either jam or jump and never what to be 0 to .005 off the lands , That just seems to be some sort of inconsistent never never land for me .

Anyways hope that made since and it's just my 2 cents

[akinswi]

well said, my magic base to ogive was 2.717, with sierras 168s For my M1s new criterion barrel It was grouping 5 shots almost in the same hole at 50yds. From a bench rest of course, I knew I had winner with that load.

Its just very time consuming measuring each bullet by the ogive with my hornady bullet comparartor.

I was thinking of doing an experiment with removing the spindle from my Forster Benchrest Seating die and dropping each bullet inside the sleeve and taking a measurement, it perfectly aligns the bullet and seems too me it would be easier to measure.

But I know the measurements would not be off the ogive , but closer to metplat as your picture shows , but I figured if those were in the same place wouldn’t the ogive be aswell?

Its also interesting that Saami has standard Cartridge overall length but no base ogive length and im assuming this has to do with different bullet types, secant ogives , tangent ogives etc.

It also makes one wonder with such violent action in a M1, that the bolt will actually put the exact same headspace between the boltface and the case head every single time, which in turn would put the ogive in different positions in the bore/leade

[Shadow9mm]

I use the eric cortina method for seating. His theory is there are several good seating nodes depending on how deep you want to seat the bullet. He uses .003 increments to test. I start at max mag length, or .020 off the lands and work back. I usually test 7 seating depths with 5 shot groups.

Im not a competition shooter. I generally have a limited budget and limited supplies so i have to make my components count and prefer to shoot rather than test.

My theory is, there are diminishing returns, and possibly more error induced testing lots of large group samples. And at some point variables like environmentals, shooter fatigue, barrel wear,
throat erosion, and fouling condition, along with others can make a bigger difference than ideal seating depth and can make it hard if not impossible to find. I feel that a very good seating depth trumps wasted components and time.

[FrankenMauser]

I may just shoot 5 , 10 shot groups between 3.310 and 3.20 and pick the best 1 then shoot for a score at SR1 target at 100 yards and go fron there.

Fives are fine, tens are good.
No point in going further, except for your own entertainment.
I have found this through my own testing.
But....

In about 2009 or 2010, I read an article titled, "The 100-shot group."
I later attempted such on my own, which I found interesting.

It was not meant to suggest firing a 100-shot group for testing, but to demonstrate the statistical significance of the various shot numbers used by different 'levels' of sportsmen to measure the accuracy and precision of their pet loads.

Measurements were taken at 1, 2, 3, 4, 5, 7, 10, 15, 20, and 25 rounds. From there, it was done at 10-round increments, from 30 to 100, with the exception of 75. (So, 75 rounds was a "bonus" increment, as 70 and 80 were also documented.)

All were shot on the same target. As such, each smaller group was a portion of the larger aggregate. (It was a very ugly target.)

All data was published, and the particular numbers for that data set indicated that the best group achieved, when using a ratio of group size divided by rounds fired (group inches / trigger pulls), was something like 47 rounds fired.

With graphs like that shared by Unclenick, the author showed everything that he could for finding the true potential of a load.

But his takeaway, which you can honestly see in Unclenick's graph, was:
20 rounds is pretty much just as good as 100, except for seeing how crazy your flyers might be in 100 rounds.
And 10 rounds is pretty much as good as 20.

His closing (and my own testing since) went something like, "I'm not wasting bullets if ten rounds will tell me what I need to know. And if five rounds is good enough, I'm not shooting ten. But three-round groups are not worth my time unless verifying zero before a hunting trip."

[Bart B.]

If you shoot at game from the offhand position, do you get a sight zero using the offhand position?

[FrankenMauser]

Do you?


I do.

[Bart B.]

Originally Posted by FrankenMauser

Do you?


I do.

Yes. And using a bullseye target, no shots have to be dead centered.

[FrankenMauser]

I haven't seen much game walking around with bullseye targets on them.

But I haven't traveled much outside of the western US and the Carolinas in the last decade. So it may be possible.

[Unclenick]

There was an old Farside cartoon about that. Two deer, one of which has a bullseye coloration pattern on his chest, and the other deer comments, "what an unfortunate birthmark."

[Bart B.]

Originally Posted by FrankenMauser

I haven't seen much game walking around with bullseye targets on them.

Have you seen any hunters take game shooting from a bench?

[FrankenMauser]

Have you seen any hunters take game shooting from a bench?

Indeed, I have -- at least within the greater umbrella of the term "hunting", as used in the US.

So far this year, I believe the whitetail count is 33 does and 6 bucks taken from an elevated blind, the shots from which are taken off a bench. An acquaintance records every kill on their ranch and shares every video.

But why circle back here? Your initial beef was an assumption that I was, somehow, not sighting rifles correctly; in a discussion that (you, yourself) detoured from seating depth testing to statistical significance of shots per group.

Now you're just picking extra nits because one of them left a bad taste in your mouth.

[Bart B.]

Originally Posted by FrankenMauser

Now you're just picking extra nits because one of them left a bad taste in your mouth.

Nothing could be further from the truth.

[Bart B.]

Originally Posted by Metal god

How many of us "really" are shooting 20rd groups during load development ?

Everyone who shoots high power rifle matches.