Does Berger Make Jump Irrelevant?

After I figure out my powder I always mess with seating to see what can happen. Here's an example


1/2" squares. Now if you put all 15 shots together it's still under 1/2" center to center POI even though seating depths vary. But the last group is pretty good on its own.

dustbag said:

After I figure out my powder I always mess with seating to see what can happen.

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That's a much better rule to adhere to. Know your powder and how to use it in your environment.

hemiford said:

I thought seating depth was only critical for peak pressures and accuracy
when nearing the lands.

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I believe that optimum seating is an abstract, unpredictable, and changing with different chambers even with same bullets.
The reason, I believe, is because seating directly causes 4 changes at once.
This is much like primer testing (another important abstract).

First I think coarse optimum seating is about matching optimum bullet-bore interface.
Second, fine barrel time
Third, pressure (also affecting time)
Fourth, neck tension (also affecting pressure and time)

Nodes that we TUNE are powder node (optimum burn), barrel node (exit timing), and system (weight/balance/rest/etc).
Prerequisites to tuning are case stability, primer/striking, and coarse seating.

As you depend on ever closer land relationships (raising starting pressure), you're accepting more sensitivity to that.
So the folks who choose to be against lands see loads collapse with erosion, and they chase lands.
The rest of us never need to chase lands.
There are some cartridges that highly reward high starting pressures. Usually small underbores.
Most hunting capacity cartridges do not need it, nor benefit from it in the long run.

hemiford said:

How do you test seating depth on a Weatherby with 3/4 of an inch freebore ?

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There are tools you can buy then there's a redneck version that seems to work about as well. You can find the video on youtube by Ultimate Reloader showing it. Basically you take a stick that will fit your barrel without too much slop, close the bolt, then measure to the exit of the barrel. Then you loosely load a bullet into a case without powder and seat that bullet with your bolt into the chamber. Use the same stick and mark the end of the barrel. The difference is a close approximation of the real max length.

I'm not as good or precise as many of you guys. I'm not the best shot in the world. I'm looking for a good hunting load under 450 yds and usually under 200. My goal is to get a good accurate bullet which seems to be closer to max length on the things I've tried. Mostly I want to avoid being too close to the lands causing high pressure.

Hikinghunter said:

So, I've worked up loads for all of two rifles, meaning my data pool is pretty limited. I'm both cases, though, seating depth just doesn't seem to matter. I start at 20 thou and it's great once I find my barrel node. Then I back up in increments to 100 just because you're supposed to try stuff. It's pointless, though. There's no accuracy difference based on seating depth.

I'm shooting Bergers (classic and hybrid hunters). Perhaps their claim about not being jump sensitive is actually true, I just have a hard time getting my head around it being totally true.

What have other people experienced with Bergers? I'm starting to think I'll just load at whatever standard COAL is and leave seating depth out of my load development process.

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After I find THE node for my rifle I load up 100 or so rounds at the seating depth that touches the lands. I shoot 5 shots at that seating depth. I had a rig welded up that inserts into my trailer hitch that I mount my single-stage press onto. So I do reseating AT THE RANGE. Every five shots is seated .005 further away from the lands. In my .243win Model 7 this process yielded a significant improvement in group size at 200yds. Went from 1.75" down to 0.75". Where in my 6.5Creedmoor Weatherby 24" barrel it seemed to make little difference. From this experience I agree that bullet jump effect on accuracy is different from rifle to rifle, load to load and shooter to shooter. It should not be dismissed as having no effect at all..

Hikinghunter said:

You guys must be able to find your lands more accurately than I can with my hornady oal guage. I get 10-20 thou variance if I try it 10 times. Sometimes you feel it as soon as it touches, sometimes you're jammed deep in the lands by the time you feel it touch. I stay 30 thou away from my average reading just to be safe.

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Clean your throat thoroughly and switch to a different bullet. You may find that it's easier to get a consistent reading.

Varmint Hunter said:

Clean your throat thoroughly and switch to a different bullet. You may find that it's easier to get a consistent reading.

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Thanks. I read some other threads written by folks frustrated with the OAL tool. Finally figured out the obvious - you can't treat a plastic tool like a metal tool. I was shoving the bullet way too far in the lands because the give in the plastic was confusing me. So I wound up sizing the neck of the modified cartridge up a touch so there's no resistance. That way I can feel the "touch" better. Also learned to very gently lock it down so the plastic rod doesn't walk on me.

This resulted in 10 readings with 5 thou from each other. I also used a cleaning rod to push the bullet back out, and paid attention to whether the bullet "stuck" in the land a bit much. Disregarded those and got 3 thou consistency.

Much more faith in my readings now. Still keeping 30 thou off the lands, just to be safe.

.

I have to shift between the bullet and the cleaning rod, back and forth multiple times with VLD style bullets.
The older tangent style bullets feel like they are hitting a wall, much easier to make the determination

my 270win with 170 EOLs like a .04 or .03 jump (i'd have to pull my data book out) I did a ladder testing from .01-.06 and it really likes the .03-.04 jump

Mikecr said:

I believe that optimum seating is an abstract, unpredictable, and changing with different chambers even with same bullets.
The reason, I believe, is because seating directly causes 4 changes at once.
This is much like primer testing (another important abstract).

First I think coarse optimum seating is about matching optimum bullet-bore interface.
Second, fine barrel time
Third, pressure (also affecting time)
Fourth, neck tension (also affecting pressure and time)

Nodes that we TUNE are powder node (optimum burn), barrel node (exit timing), and system (weight/balance/rest/etc).
Prerequisites to tuning are case stability, primer/striking, and coarse seating.

As you depend on ever closer land relationships (raising starting pressure), you're accepting more sensitivity to that.
So the folks who choose to be against lands see loads collapse with erosion, and they chase lands.
The rest of us never need to chase lands.
There are some cartridges that highly reward high starting pressures. Usually small underbores.
Most hunting capacity cartridges do not need it, nor benefit from it in the long run.

Click to expand...

At what distance from the lands do you steer clear of this situation? Is it is you are not touching the lands, or does there need to be some additional distance?

hemiford said:

How do you test seating depth on a Weatherby with 3/4 of an inch freebore ?

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Go to wheeler accuracy. He has a video to find the lands that is as consistent as it gets. You can measure your rifle and your buddy can measure it next and get the same number. You'll need to to take your bolt apart, but since since you already have it apart its a good time to clean anyhoo.

The Oregonian said:

At what distance from the lands do you steer clear of this situation? Is it is you are not touching the lands, or does there need to be some additional distance?

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I do full seating testing with exception of touching (ITL) (I don't go that far).
Normally starting ~5thou off the lands (OTL) working back.
I do this because I don't care if 'best' could have been touching or maybe jammed, because that land relationship is too precarious for me.
Too fleeting.

I want to find 'good enough' somewhere well away from land touching, so that I never have to mess with coarse seating again, for the accurate life of that barrel, with that bullet. And ~1800 rounds down the road, when my results take a step change, I don't have to think that it's time to chase my tail with a bunch of retesting. Instead, I think it's time to screw another barrel on. Simple as that.

So, 5thou back,, how do I know that?
I check for land distance (touching CBTO) with a new barrel, log that, and make a dummy round with it. This, with a cleaning rod method.
If lands are far enough out that touching is beyond where I would put bullet bearing in necks, then I begin at furthest acceptable CBTO.
And there I don't care what my land relationship actually is. I only care about a tested best CBTO -that is not ITL.

Several years ago Mark Gordon of Short Action Customs did a very in-depth study of bullet jam/jump and the results are on the Precision Rifle Blog. See the like below. There are a number of things that can affect the POI on any given shot and most people accept that seating depth is one of them. Even in the case of expert shooters much of the information is based on anecdotal (observed) evidence but there is a preponderance of it. However much of the data is from shooter/rifles weighing over 13.5 lbs and capable of producing 5 shot groups in the teens (<.2MOA) at 100yds repetitively. These are the top shooters in the world shooting rifles specifically assembled for producing accurate, precise groups. On the other hand your typical hunting rifle weighs around 8 lbs and is probably only capable of consistent .5 MOA groups even with a top shooter driving. Varying seating depth and comparing the results in these two extreme cases is going to produce very different results. In the hunting rifle it is likely that the true effect of the seating depth change is lost in the noise (other effects).

This is the first of two articles.

Kieth Glasscock of Winning in the Wind recently did a test of his F Class seating depth using larger sample sizes and found some interesting results. This video can be seen here: