Purpose of bullet jump

[DUSTY NOGGIN]

look at it like three different adjustment knobs with each knob affecting the variations of the other 2 knobs .. one knob may adjust more than one variable , so using another knob to split the variables of a previous knob

seating adjust knob
low (away from lands) affect the average momentum required to overcome the swaging into the bore . plus can affect bullet leaving muzzle timing
high (close to lands) lessens the average momentum predictability of the swaging into the bore ( while at the same time creating pressure changes ) .. also affects bullet leaving the barrel timing

 

[adam32]

I just prefer to shoot quality built rifles and good bullets then all the testing nonsense goes out the window.

If I had to do all the work that's been posted in this thread to get 1/2moa groups I would get the rifle rebuilt. It's not very difficult to get a rifle to shoot well if the rifle is good to start with.

 

[nmbarta]

Your basically making adjustments to the pressure curve when you play with seating depth.

As you seat deeper you decrease case capacity which increases pressure, but at the same time you allow for more momentum when the bullet engages the lands, which decreases pressure.
So, you may find two loads at different seating depth and powder charges that have the same peak pressure, but the time that shot is at peak pressure has changed. You've changed the shape of the pressure curve if your looking at a graph.

The shortest answer I could give, is pressure curve. I believe that is what is being "adjusted" the most by changing your seating depth, this will change exit timing, but I don't think it's just velocity that causing the change in exit timing as the harmonics have been changed as well. I'd have to be quite a bit smarter than I am to completely understand everything going on with internal ballistics, but changing your seating depth probably has some effect on just about everything internally.

 

[Mikecr]

While seating changes do affect matters of tuning, seating itself affects results far beyond all other tuning parameters. I can add ~1moa to pretty much any combination while doing full seating testing.
And slight affects to tune(from anything) do not cause ~1moa changes.
It isn't tuning

 

[nmbarta]

While seating changes do affect matters of tuning, seating itself affects results far beyond all other tuning parameters. I can add ~1moa to pretty much any combination while doing full seating testing.
And slight affects to tune(from anything) do not cause ~1moa changes.
It isn't tuning

Would you mind explaining exactly what your referring to in regard to "tuning"? I think that most refer to "tuning" as anything your doing to refine your reloading and accuracy in said rifle. I'm picking up that your referring to something more specific when it comes to "tuning". I think of tuning as more of a barrel harmonics situation, but may not have a good grasp on the specifics in this particular situation.
I'd like to learn a bit more about that.

 

[Lefty7mmstw]

I just prefer to shoot quality built rifles and good bullets then all the testing nonsense goes out the window.

to a point...I tend to not shoot something that's extra fussy.

Would you mind explaining exactly what your referring to in regard to "tuning"? I think that most refer to "tuning" as anything your doing to refine your reloading and accuracy in said rifle. I'm picking up that your referring to something more specific when it comes to "tuning". I think of tuning as more of a barrel harmonics situation, but may not have a good grasp on the specifics in this particular situation.
I'd like to learn a bit more about that.

read the above posts... it's how the bullet interacts with the bore itself more than timing or pressure... pressure doesn't change much in a few thou. unless you approach jamb.

 

[Mikecr]

Please bear with an analogy here:
If you cause a high chamber end clearance then gases can migrate backward around the necks to affect neck sealing, and velocity spreads. A carbon ring forms so results can keep changing. Reducing that chamber end clearance to alleviate the issue can affect your tune better/worse. It is possible to creep into/out of tune with case trim lengths, not only because of end clearances, but by adding/subtracting neck brass that is gripping bullets (tension). But this is not commonly acted on as tuning.
Case trim is considered a precondition, which we establish with intent to maintain, PRIOR to tuning.

Now wonder;
COULD case trimming be considered tuning? COULD we shoot 'sine waves' through case trimming? YEP,, and YEP
Should we? NOPE,, and NO WAY

I submit that tuning, and preconditions for tuning, are different animals.
That bullet seating, primers, and case/chamber fitting are preconditions.
Testing is absolutely needed to establish these preconditions as best.
But this testing is not tuning.