Does Berger Make Jump Irrelevant?

[dustbag]

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.

 

[FEENIX]

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

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

 

[Mikecr]

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

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.

 

[sjt18]

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

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.

 

[emp1953]

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.

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..

 

[Varmint Hunter]

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.

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