Bullet Jump/Jammed - Is it the Bullet design or the rifle

asd9055

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I have been reloading for hunting and hand guns 35 years. I did not realized how little I knew until I started following and participating in forums like LRH, Nosler, Accurateshooter and snipershide, to name a few.
I don't want to get into OCW, Ladder and all those other subjects for load development. I just want to focus on bullet seating depth (jump or jammed)
I am familiar with bullet seating depth process, and I posted a link here before, but the engineer in me wants to understand more.
So here is the question I pose to the greater and more experienced group:

Is it the bullet design, i.e. tangent vs. secant that determines the jump/jammed, the caliber/cartridge (we know Weatherby cartridges are designed for extra long jump, the rifle (way the chamber and throat, barrel, lead come together) or a combination of all

Second question. Do you have a cartridge. let's say 6.5 Creed (pick one that applies to you) that you use a different seating depth for different rifle (same bullet)
I am trying to understand the physics/mechanics behind it
 

dok7mm

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I never jam a bullet in a hunting rifle, with the exception of forming wildcat brass, so let's set that aside.

Seating depth is used primarily for fine tuning your accuracy powder node.

First thing is magazine length, your OAL should determine where you start. From there, you can only go deeper to find the jump that is the most accurate.

Some bullets will shoot well in different rifles with same jump, but only in similar barrels in my experience.

Lot's of things make a difference in seating depth: barrel harmonics, reamer specs, powder & charge wt and even neck tension.

I gave up long ago trying to guess what jump will work with each bullet, I test with .015" - .020" jump to find best powder charge, then do a full seating depth test on each bullet I plan to shoot.
 

Doom2

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With the development of more aerodynamic secant ogive bullets, it seems that they are more sensitive to variations in seating depth. This has generally been attributed to less bearing surface. You may find the following article of interest.

 

Laguna Freak

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With the development of more aerodynamic secant ogive bullets, it seems that they are more sensitive to variations in seating depth. This has generally been attributed to less bearing surface. You may find the following article of interest.

This PRB article and the related are helpful for sure.

I flip dok7mm’s assessment 180 degrees and this is new in my world. In my load development, I now use seating depth as the first and coarse adjustment step. Then fine tune with powder charge.
 

asd9055

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With the development of more aerodynamic secant ogive bullets, it seems that they are more sensitive to variations in seating depth. This has generally been attributed to less bearing surface. You may find the following article of interest.

There are a couple of articles by him actually and I have reference them before. I am trying to understand the mechanics and is it the bullet, the rifle, the cartridge..
 

asd9055

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This PRB article and the related are helpful for sure.

I flip dok7mm’s assessment 180 degrees and this is new in my world. In my load development, I now use seating depth as the first and coarse adjustment step. Then fine tune with powder charge.
There are a couple of articles by him actually and I have reference them before. I am trying to understand the mechanics and is it the bullet, the rifle, the cartridge..
I am not questioning the methods...I just always try to get the why
 

asd9055

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Let's say you have a pet load for one caliber. Let say it is 180 grns secant type bullet. Let's say it likes to jump 0.040". If you load a 180 grn "tangent" type bullet, same rifle, same everything else, will it be the same 0.040" jump?
 

aushunter1

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I never jam a bullet in a hunting rifle, with the exception of forming wildcat brass, so let's set that aside.

Seating depth is used primarily for fine tuning your accuracy powder node.

First thing is magazine length, your OAL should determine where you start. From there, you can only go deeper to find the jump that is the most accurate.

Some bullets will shoot well in different rifles with same jump, but only in similar barrels in my experience.

Lot's of things make a difference in seating depth: barrel harmonics, reamer specs, powder & charge wt and even neck tension.

I gave up long ago trying to guess what jump will work with each bullet, I test with .015" - .020" jump to find best powder charge, then do a full seating depth test on each bullet I plan to shoot.
As I was saying in another thread nealy everything about the rifles action/bedding, even bolt string tension & component choice will determine the timing of the barrel, that what your trying to do in reloading.

I am no ballistics expert or smith but when your changing the CBTO your playing with the pressure waves.
Regardless of the ogive your just trying to find that spot where with everthing combined give you the node.

And then you could throw in the use of a barrel tuner & probably jump or CBTO becomes more forgiving.
 

dok7mm

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This PRB article and the related are helpful for sure.

I flip dok7mm’s assessment 180 degrees and this is new in my world. In my load development, I now use seating depth as the first and coarse adjustment step. Then fine tune with powder charge.
I am basically using a rough seating depth, but it's not as concise as the "rough seating depth first method". I've tried both ways, but prefer powder charge first. Both get to same end.
 

Mikecr

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I have a different view on what seating is doing, that I believe passes more tests.
In my view, seating adjustments affect a bullet's quality of interface with a given leade. The shapes and ratios of either changing what appears best. With this, the load itself does not matter, as this seating attribute is not tuning, but still prerequisite to best accuracy (for many).

Picture lottery ping pong balls sucked into an overhead tube. Some slip right in while others rattle a bit on entry.
If you were to set up a jig that fired ping pong balls toward another tube opening, you might see just the same while firing from different distances.
For our application, I think what is most consistent is best.

I'm sure that changing the ping pong ball shape affects this, makes sense, but nobody credibly predicts a given change. Most claims, until locally proven(tested), are merely conjecture or merchandising.
 

misterc01

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Have you read "Hand loading for Competition - bringing the Target Closer" by Zediker? He cover this in some detail. He also goes into the difference between secant and tangent bullets, plus short vs longer, round nose and flat base bullets. After reading it - my general conclusion is some rifles like different amounts of jump - from into the lands to way, way back.
 

asd9055

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Cant find that, but I can find "Handloading for Competition Making the Target Bigger" by same author.
I am not looking on "how to", I am looking on what/why, the physics. Is it the bullet design, the rifle, the cartridge...i.e., Weatherby mag vs win mag vs prc or Creedmoor. We know Weatherby designed his with extremely long jump.
 

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