The question of seating depth on the accuracy has been discussed many times.

We wanted to see if can run a test on this subject.

The idea to run the test on 2 or 3 rifles of different calibers.

First rifle we have is a Remington 40X in 222 Remington.

The idea is to shoot 5, five shot groups at the maximum over all length for this cartridge.

Then use the same load, and reduce the length in progressive increments as far as feasible.

and fire 5, five shot groups.

Then use the same load, and increase the length in the same increments as far as the rifle will handle.

And fire 5, five shot groups.

My question is, how much are these increments should be??

Here are our test results

I'd propose increments of 0,5 mm (.02").

I think the first consideration is why would seating depth make a difference at all? I believe it's because of differences in alignment of the chamber with the barrel be they however minute, differences in throat, differences in chamber, etc. that one can accomodate for by differences in seating depth. In other words, seating depth can make up for some of the aformentioned inaccuracies. If you had a perfectly chambered rifle and ammunition that fit the chamber perfectly then seating depth probably wouldn't make nearly as much difference.

Since the part of the bullet that has to do with alignment with the bore is that portion of maximum diameter between the base of the bullet or where a boat tail starts and the start of the ogive. I would use a ratio of said distance such as 1/5th or 1/10th.

Berger (of Berger Bullets) has some very specific recommendations about findings the optimum seating depth.

Load-up some ammo (6 rounds each) with COAL as follows:

0.010" into or touching the lands
0.030" off the lands
0.070" off the lands
0.110" off the lands

or - if you're worried about pulling the bullet

0.010" off the lands
0.050" off the lands
0.090" off the lands
0.130" off the lands

One of these will shoot much better than the rest. Once, you find it, you can tweak the distance even more.

This technique has been published. I suggest getting a copy of the Berger Bullets reloading manual (1st edition) and reading the chapter by Eric Stecker on "Berger Bullet Products", especially those sections on the VLD bullet design and "getting the best precision and accuracy from the VLD bullets in your rifle".

Saeed,

To some extent, this is bullet dependent. My experience with cup and core bullets is that the seating depth for accuracy usually isn't so critical and it tends to be more linear than when using monos. My experience with monos leads me to believe that .005 inches can make a huge difference in some rifles while others seem relatively unphased by any difference in seating depth. To complicate matters a little more, a rifle may be much more critical of one brand of mono than another.

I suspect you may wind up measuring bullet sensitivity to seating depth every bit as much as you will be measuring rifle sensitivity.

Perhaps the first task might better be trying to define a benchmark test for a given rifle and then a benchmark test for a given bullet.

This will be a very worthy series of tests, but it will be very, very difficult to find a starting place (benchmark). Perhaps, the best benchmark might be to define the greatest accuracy a rifle is capable of with a given bullet and powder, and then to be able to describe what happens when you deviate in either direction from that with a statistically valid number of bullets and rifles. From that, with a little luck there may be some decent usable predictability might emerge.

I usually go in increments of .020 (twenty thousandths). Working in increments of .005 has not proven viable to me.
Why should it make a difference? Good question, but sometimes it does, sometimes not. Each rifle is an individual.

OK, here is the plan.

I picked a load that shoots reasonable well in this rifle - Remington 40X in 222 Remington.

It is 19.6 grains of VVN 130.

I have not tried to find a better load, for the simple reason that we want to see if there is any improvement in seating depth.

The load is the starting load in the Vihtavuori manual with this powder and a 52 grain bullet.

That load was loaded to 2.130"- as it is the maximum over all length for this cartridge.

The maximum length I can load for this rifle, bullet jammed into the rifling, is 2.310.

I have loaded 25 rounds at this length, and will shoot them in 5 shot groups.

I will load another 25, 0.020, increments, and see what happens.

I would suggest using a different rifle. If you're using a 40X in .222, you should be shooting ragged holes with any reasonable loading. Which would make them very hard to measure. Even with bench rest equipment.

quote:

Originally posted by wasbeeman:
I would suggest using a different rifle. If you're using a 40X in .222, you should be shooting ragged holes with any reasonable loading. Which would make them very hard to measure. Even with bench rest equipment.

Please explain . Why ???

Bartsche,

most 40X's in 222 shot under 3/10ths at a hundred yards out of the box. For many years they owned bench rest LV and HV in 222 and the 6mm/222 Magnum in Sporter Class.

They are still likely the most accurate factory rifles in the smaller calibers.

.025

Were it me I would start .010 into the lansa and back out in .005 increments.

That's what I do with my accuracy stuff once I find the powder....

.025 is huge in a .22 or 6mm....

.

Here is our initial results.

I will post photos at the end of my test.

As I mentioned, no effort was made to establish a best load for this rifle.

I have plenty of VVN 130, so I thought I will use that.

I took the starting load in the Vihtavuori book, which was 19.6 grains of VVN 130.

The bullet is Bill Brawand 52 grain match flat base.

Bullet jammed into the rifling, at an over all length of 2.310 inches.

Groups

0.285
0.303
0.320
0.535
0.319

Average 0.3524

2.290"

0.509
0.435
0.277
0.336
0.569

Average 0.4252

2.270"

0.362
0.393
0.353
0.514
0.497

Average 0.4238

2.250"

0.600
0.219
0.251
0.373
0.386

Average 0.3658

2.230"

0.518
0.407
0.400
0.473
0.573

Average 0.4742

2.210"

0.364
0.493
0.464
0.698
0.294

Average 0.4626

2.190"

0.304
0.364
0.350
0.268
0.514

Average 0.3600

2.170"

0.366
0.392
0.729
0.320
0.533

Average 0.4680

2.150"

0.528
0.522
0.426
0.542
0.373

Average 0.4788

2.130" This is the maximum over all length for this cartridge.

0.358
0.307
0.338
0.735
0.567

Average 0.4610

2.110"

0.539
0.222
0.269
0.402
0.264

Average 0.3392

2.090"

0.595
0.479
0.177
0.542
0.569

Average 0.4724

We had a bit of discussion here at these results.

There is really not that much between them to warrant any hard conclusions.

For example, if we had fired all the groups with exactly the same over all loaded length, we might have gotten the same results.

I am going to continue this 0.020" reduction in each lot, until the whole of the shank of the bullet is seated into the case.

Saeed, all of the information i have written by the bench rest shooters recomend changing bullet distance from the lands to the bullet in .010 incriments and then when the best is found try seating .005 more and .005 less to see if theres an improvement. i see the results you have gotten in your reloading pages and have to ask how did you determine what seating depth to use.

There is probably alot of information about this on the benchrest.com site.

Phil,

If you read my post above you will see how I arrived at a starting point.

Changing seating depth by 0.010 is not going to work with our bullets, as the length of each bullet varies by as much as 0.007 or may be more.

Also, as the results above show, there is no discernible differences in the groups shot so far.

I'm with JTEx. I always start at .010 off, or at least use the max OAL that your magazine will allow, and work up charges at .5gr increments until you start seeing pressure signs. I will then take most accurate loads and start seating deeper by .025 increments. Starting out near the lands leaves only one way to go.....seat deeper. I don't usually worry about SAAMI OAL unless the magazine dictates it.

i was asking about the seating depth used in reloading pages section of the web site.

More results have been posted.

quote:

Originally posted by Idaho Sharpshooter:
Bartsche,

most 40X's in 222 shot under 3/10ths at a hundred yards out of the box. For many years they owned bench rest LV and HV in 222 and the 6mm/222 Magnum in Sporter Class.

They are still likely the most accurate factory rifles in the smaller calibers.

thank you! roger

Saeed. Did you use new brass in your seating tests? If fired cases were used, did you full size or neck size only?

Brass was from SAKO.

It started life as factory ammo, and I think it was fired one or two more times.

We full length sized after each firing, trimmed after 4 firings.

I am processing the photos and will post all the results soon.

Thanks for your answers. That was very thorough. I appreciate the effort. I am very curious if the neck and case body expansion was spot checked before you full-sized and trimmed the cases and if so, was the expansion minimal?

Neat stuff, Saeed. roger

Practically and maybe even mathematically, if done according to scientific method, with lots of duplicate results for each OAL selected -- that's all the same group.

quote:

Originally posted by BNagel:
Practically and maybe even mathematically, if done according to scientific method, with lots of duplicate results for each OAL selected -- that's all the same group.

Several groups all nearly identical. Wasbeeman had it right.

We have reached the same conclusion as many of you.

That, at least in this rifle, seating depth does not necessarily make much of a difference in accuracy.

I wish high school would have been this interesting. I may have paid more attention.

quote:

Originally posted by custombolt:
I wish high school would have been this interesting. I may have paid more attention.

May be you had the same problems we all had.

GIRLS!

Guilty as charged. You should have seen Ms. Gree----ger and A. B. The dreams remain.

Thanks for the info. Great data, answers some of the questions I had concerning seating depth

Interesting info. Thanks, Saeed, for your work on this.
There was an article in one of the gun mags a couple of years ago. The writer was working up loads. In one instance, he changed seating depth by a small amount. I forget now what it was but it was relatively small. His group shrank by a large percentage. His conclusion was that seating depth, or OAL, was a major factor in tightening groups.
My personal experience, and I have been working on this off and on since reading the article, is that I can discern no difference in group size by changing seating depth.
My rifles are basic hunting rifles that I work with and usually find a load or two, or in some cases many loads, that shoot into the magic MOA.
I have also found lots of group size variation by shooting the same load on different days and especially under different light conditions.
And, finally, where I live, it is usually windy and I know that even a small wind will negatively affect group size.

For my own hunting rifles, the seating depth is governed by what fits in the magazine.

Under normal reloading conditions, I normally load my ammo to the maximum spec of that particular cartridge.

Years ago I read an article by someone loading the 30-378 Weatherby Magnum.

He said he needed slightly more velocity, so he added something like 0.7 of a grain, and he got exactly the velocity he desired.

As you can imagine, I stopped believing anything that writer published.

Reassuring for me with my love of the .375 Wby throat.

quote:

Originally posted by Saeed:
For my own hunting rifles, the seating depth is governed by what fits in the magazine ...

But for the .375/404 on a Dakota 76 action with a 404 Jeffery boltface and a 416 Rigby magazine box length, it also depends on the throat of the chamber and the nose shape of the bullet projecting forward beyond the case mouth.

I am still wondering what kind of throat Saeed has used on his .375/404 Jeffery Saeed of 1996.
I am guessing it is a zero-free-bore throat, with only a leade, because his .375/300-grain Walterhog long-nose bullet is all sub-caliber, high-ogive number, beyond the case mouth.





Will Saeed ever reveal his chamber throat specifications for the .375/404-JS-1996?


Saeed made the moly-coated one, Bridger Bullets made the plain copper copy, pictured below.
That is an early Walterhog, Saeed has tweaked the hollowpoint depth and who knows what else since then.
here was about 0.830" of nose projection ahead of the first skinny drive band of 0.375" diameter.
The nose ahead of that drive band is 0.365" diameter and only gets smaller as you go forward.
The solid white-line squares are centimeter ruled. The dotted white-line squares are 1/2 inch ruled:



In this photo by Saeed below, it looks like he is seating the Walterhog pretty deep.
Must have zero free-bore in that rifle, eh?



So what is the diameter at the start of the leade, and what is the leade angle?

Here is another famous zero-free-bore throat, that of the .416 Rigby according to C.I.P.:



I would love to be able to draw the throat of the obscure .375/404 Jeffery Saeed of 1996,
as opposed to well known throat specs of the
.375/404 Jeffery Saeed of 2012,
where free-bore diameter of 0.3756" is only 0.0006" greater than bullet diameter, but it is almost one caliber long at 0.370":

With the .375/404 Jeffery Saeed of 2012 a .375-caliber Impala "Groovy" bullet was used to make a Go and No-Go gage for throat effect on C.O.L. with a full-caliber bullet diameter in the nose:



The same bullet was used to show a Go gage for CZ 550 Magnum magazine box length,
and some useable C.O.L.s with various bullets:



And the bottom bullet in the photo below shows that I can seat Walterhog bullets
or GSC HV or Barnes TSX bulletsout to 3.820" C.O.L. in my CZ 550 Magnums
that are chambered for .375/404 JS-2012:

Here is a great varmint bullet load (Barnes .375/250-gr TTSX) that Saeed might have to seat deeper in his rifle:

Rehashing all my old stuff?
Well, Saeed has never revealed enough info for me to reverse-engineer the throat.
Years of begging.
So I continue to beg and seek attention with what little I have.

How About this, Saeed?

Get a full-diameter, flat-based .375-caliber bullet like the Impala I used above,
or just machine a piece of your copper rod to .375 diameter and true cylinder base about as long as a Walterhog,
then seat it in a cartridge case, flat base forward, and see how long the go and no-go C.O.L.s are?
Like this:



Inquiring minds want to know.