Seating Depth

[desertbandit]

Hi again....I just posted a thread about disagreeing that .001-.003, makes any difference in accuracy...I sure got informed otherwise, LOL....I'm not a BR shooter or have any of their fancy reloading equipment....I don't even know what they use...I use a Dillon press with either Redding or Foster Comp. dies....All my rifles are the hunting type....I have about everything from a .223 to a 35 Whelen...All of them will shoot sub MOA, most of them sub .5 MOA....Excuse me BR shooters, but I'm low tech, not high tech.....But I do know, when seating a bullet, the depth will change, depending how you operate the press, fast stroke vs. slow stroke....Also, I measure off the ogive with a comparator and depending whether you have a light touch or a hard touch with the calipers, you'll get different readings, by quite a few thousands...That's my reason for stating .001-,003 makes no difference, at least in the way I reload......Good Shooting Everyone...

 

[Bc'z]

So I've been working with measuring OAL of bullet as my only sorting method.
What I'm seeing is a more consistent CBTO measurement,
.001-.0015 variation.
Keeping in mind your seater stem dosen't contact the bullet in the same location as comparitor.

 

[RegionRat]

Not every system will show a strong response to a 0.001” - 0.003” change, but some certainly do.
Some of this depends on the interplay near jam, where small changes can mean pushing the pressure up several thousand PSI. Sometimes it is about the exit timing combining with the pressure, other times it isn’t. The only way to know is to try.
Keeping in mind that the system (not to mention the driver) has to be capable of showing small groups to begin with or the effect gets buried in the noise.
With many guns, you will see effects from seating depth sweeps that are nearly as strong as the powder charge sweeps, but with others you have such a large dispersion you can barely see anything at all. YMMV

 

[INTJ]

This site is one of the top two sites for BR shooters. It may be #1. As a consequence, you need to expect when you make statements about such and such being so, that you will very likely get pushback from BR shooters. Most people have no idea how well BR rifles shoot and what we do to get them that way.

So if you say that seating depth changes of .001 - .003" don't matter, you will get a BR shooter telling you how he was able to shoot 2" groups at 1000 yds by making those type of changes.

Now if you say up front it is a hunting rifle, then you will probably avoid the pushback. For a hunting rifle I start seating at .020" off the lands. I won't go closer than .010". When testing seating depth for a hunting rifle I might do something like this:

.010 off
.015
.020
.025
.030
.050
.075
.100

For a BR gun I usually find best accuracy for .021 Jam from touch to .018 jump, depending on the cartridge and bullet. I use .002 to .003" increments for those rifles.

 

[RegionRat]

https://precisionrifleblog.com/2020/04/05/bullet-jump-load-development-data/

I’ll just leave the link with a reminder to use the links in the article and read the whole series of seating depth articles from the beginning.
That blog is not BR shooting but more about PRS or Highpower that tends to require magazine feed and pre loaded ammo, so probably more related to non-BR shooting. If anything, the raw data of the seating depth tests across several rifles and over such wide sweeps may be enlightening to beginners.

 

[desertbandit]

This site is one of the top two sites for BR shooters. It may be #1. As a consequence, you need to expect when you make statements about such and such being so, that you will very likely get pushback from BR shooters. Most people have no idea how well BR rifles shoot and what we do to get them that way.

So if you say that seating depth changes of .001 - .003" don't matter, you will get a BR shooter telling you how he was able to shoot 2" groups at 1000 yds by making those type of changes.

Now if you say up front it is a hunting rifle, then you will probably avoid the pushback. For a hunting rifle I start seating at .020" off the lands. I won't go closer than .010". When testing seating depth for a hunting rifle I might do something like this:

.010 off
.015
.020
.025
.030
.050
.075
.100

For a BR gun I usually find best accuracy for .021 Jam from touch to .018 jump, depending on the cartridge and bullet. I use .002 to .003" increments for those rifles.

I usually start .020 off, then go in .010 increments, then if I find one that is close, I go .005 high and low...I have had pretty good luck with that.

 

[desertbandit]

https://precisionrifleblog.com/2020/04/05/bullet-jump-load-development-data/

I’ll just leave the link with a reminder to use the links in the article and read the whole series of seating depth articles from the beginning.
That blog is not BR shooting but more about PRS or Highpower that tends to require magazine feed and pre loaded ammo, so probably more related to non-BR shooting. If anything, the raw data of the seating depth tests across several rifles and over such wide sweeps may be enlightening to beginners.

Thanks...I'm going to do some reading on it...

 

[D Coots]

If a person can't tell the difference on the target of .001-.003 he does not have a very accurate rifle. Or possibly needs a better setup or needs to become a better shooter.

PS.......or he has a great barrel.

Later
Dave

 

[Lucky Shooter]

For many years my loads for the dog towns used seating depths ranging from
"slightly" into the lands to a few thousands deeper into the lands -----never had any success
at or close to "full jam". This method seemed to get tuned to a "good but not necessarily
optimum" slot without wasting too many shots.

I'm now playing with a 222 that has shown me that some good tunes occur slightly,
.005" to .010" off the lands.

I haven't tried seating further into the lands but plan to look for a good tune that's
further into the lands. I've never found success at or near full jam but haven't given up on
the idea that a bullet "somewhere into the lands" has a better chance at good bore alignment.

I hear the word "jam" used a lot and wonder how successful others have been at a true
full jam-----am I missing something good ?

I'd appreciate hearing more about success at full jam.

A, Weldy

 

[powderbrake]

For many years my loads for the dog towns used seating depths ranging from
"slightly" into the lands to a few thousands deeper into the lands -----never had any success
at or close to "full jam". This method seemed to get tuned to a "good but not necessarily
optimum" slot without wasting too many shots.

I'm now playing with a 222 that has shown me that some good tunes occur slightly,
.005" to .010" off the lands.

I haven't tried seating further into the lands but plan to look for a good tune that's
further into the lands. I've never found success at or near full jam but haven't given up on
the idea that a bullet "somewhere into the lands" has a better chance at good bore alignment.

I hear the word "jam" used a lot and wonder how successful others have been at a true
full jam-----am I missing something good ?

I'd appreciate hearing more about success at full jam.

A, Weldy

My definition of "full Jam" is having the bullet seated longer, and putting the cartridge in the rifle, and closing the bolt, thus pushing the bullet into the lands at "full Jam", and back somewhat in the case.
In my experience, benchrest shooters use this method, then they deduct some number, like .007, and seat there to start. Then they adjust in either direction to best group.
Of course, the amount of jam you have is dependent on the state of the lands, and on the fit of the bullet in the case (amount of diametric interference) and the neck wall thickness, and it obviously varies from rifle to rifle, and with case fit.

You are not missing anything.

It is still a relative measurement, and you adjust your seating depth from that point, and let the target tell you when to stop adjusting.

I suggest it is easier to use a Hornady OAL gage to find the start of the lands. (Suggestion, Hornady seems to want you to press on the gage very very softly. I suggest you press firmly but not so hard that you feel it "click" into the lands)

Better yet, use the Wheeler methods to find case sizing and seating depths. Very repeatable.
https://www.wheeleraccuracy.com/videos

 

[BoydAllen]

The last from scratch workup I did was trying H322 with Bart's 52s in my tight neck .222. I found excellent accuracy at jam (bullet moved when chambered) up near where I was getting some pressure. It put three in the mothball with none touching the inside of the line.

 

[JFrank]

If a person can't tell the difference on the target of .001-.003 he does not have a very accurate rifle. Or possibly needs a better setup or needs to become a better shooter.

PS.......or he has a great barrel.

Later
Dave

Or perhaps the bullets being used are simply a forgiving design, or the tune window i wider on that particular firearm.
I think what the OP was referring to is being able to manipulate the reading on the calipers which anyone can do.

 

[desertbandit]

If a person can't tell the difference on the target of .001-.003 he does not have a very accurate rifle. Or possibly needs a better setup or needs to become a better shooter.

PS.......or he has a great barrel.

Later
Dave

I'm talking production rifles...Hunting rifles..

 

[RegionRat]

I'm talking production rifles...Hunting rifles..

There were so many different ways that different companies viewed their chambers and throats, that the only way you will know is to test.

ETA: A wide single sweep at long distance should be good enough to show if there are any useful vertical nodes. Then, you could go back to any spots that looked promising and test with groups.

 

[Lucky Shooter]

I've used the Wheeler end of the scale as a reference and have avoided using the
jam as either a reference or a working load.

Boyd comes along and finds sweet stuff at jam. This makes me think I should at
least give the jam end of the range a fair try-----hope to keep it simple.

Am I correct to say I have full jam when a loaded round exits the chamber shorter
than when it went onto the chamber ? Sometimes when an effort gets very simple,
something important has been left out.

I'm somewhat surprised the 222 has (so far) shot better seated out of the lands.

Live and learn.

A. Weldy

 

[JFrank]

I've used the Wheeler end of the scale as a reference and have avoided using the
jam as either a reference or a working load.

Boyd comes along and finds sweet stuff at jam. This makes me think I should at
least give the jam end of the range a fair try-----hope to keep it simple.

Am I correct to say I have full jam when a loaded round exits the chamber shorter
than when it went onto the chamber ? Sometimes when an effort gets very simple,
something important has been left out.

I'm somewhat surprised the 222 has (so far) shot better seated out of the lands.

Live and learn.

A. Weldy

That’s called soft seating and doesn’t work well at long range.
I use enough bullet hold to seat .025 into the lands and still be able to eject a loaded round without loosing my depth setting.

 

[RegionRat]

Am I correct to say I have full jam when a loaded round exits the chamber shorter
than when it went onto the chamber ? Sometimes when an effort gets very simple,
something important has been left out.

”Jam” is not a fixed physical constant or rule of physics once you put a light on the subject.

Two different bbls cut with the same reamer can come close to the same jam numbers, but even then the point I am trying to make is those jam values don’t mean anything if we try and transfer them to a different bullet and certainly not to a different gun.

Jam is something you test once you have a starting value as a guide, it isn’t a dimension on a blueprint. There is a gray scale from touching to beyond engraving that can be debated, but it isn’t worth arguing. It isn’t easy to define in terms of force or displacement, yet it can be managed In practice.

 

[darkangel_r2]

That’s called soft seating and doesn’t work well at long range.

Pretty sure John Whidden won some palma nationals doing that. I think it works fine if you have a good tuner.

 

[JFrank]

Pretty sure John Whidden won some palma nationals doing that. I think it works fine if you have a good tuner.

I can’t speak for others but what ive documented has been irregular grouping rather than printing without unexplained fliers and weird groups.
Try for yourself and report back