Jump Measurement Shorter?

[Bob Wright]

Think of 2 things when reloading:
-Your seater stem will set the bullet depth into case.

- The ogive will vary to the length of the bullet, regardless of the base or point of the bullet you measure from. It's tolerance.

Clean the gun well and measure, but without the original bullet used in the measurement you have some tolerance.
Also check your measuring comparator to be sure it's the correct caliber.

 

[General RE LEE]

So you can be twenty thou off lands with one lot and touching or jammed in lands or another. Interesting and seems a lot of folks load 15 to 20 off and can run into serious pressure spikes if running on edge.

 

[can1010]

I think what @asd9055 is saying is if you load every projectile to touch the lands on the ogive, the cartridge base to ogive will not change as long as nothing in the chamber has changed. If the ogive is farther back on the bullet the coal will be longer. If the ogive is farther forward the coal will be shorter.

the original post is about changing measurements as throat wears and the weird measurement he was getting and possible causes.
if your checking comparison measurements you need to compare apples to apples and that means using the same bullet, same technique, same tools, same stage of cleaning. didn't think this was so hard to understand, you cant change something in the system when using comparison measurements and expect accurate results.

 

[can1010]

So you can be twenty thou off lands with one lot and touching or jammed in lands or another. Interesting and seems a lot of folks load 15 to 20 off and can run into serious pressure spikes if running on edge.

that was the worst I have seen, normally.003-.005 between lots. nobody wants to believe it but then again very few save the original bullet and checks the new lots against the original.
if you're a book reloaded like so many, none of this matters but when you're trying for the most accuracy possible every detail matters.
I load certain bullets with as much as .012 jam and some at .003 off so even small changes matter that is why i went to purchasing large lots to help eliminate the problems.

 

[Seabeeken]

That has nothing to do with where the .308 ogive will hit the lands. Only effects the COAL. Its math, physics, geometry, call it what you want...but I am out...not my topic....

I think what he is trying to say is the position where the seating stem contacts the bullet will vary by lots and thereby changes the ogive measurements. If the stem seated off the ogive, it would remain constant

 

[Weaver93]

the original post is about changing measurements as throat wears and the weird measurement he was getting and possible causes.
if your checking comparison measurements you need to compare apples to apples and that means using the same bullet, same technique, same tools, same stage of cleaning. didn't think this was so hard to understand, you cant change something in the system when using comparison measurements and expect accurate results.

That's why I said "if nothing in the chamber changes." I was not disagreeing, just stating where I thought the confusion was.

 

[cb186]

The amount of force you use when pushing the bullet in with the comparitor will effect your measurements. The longer the freebore, the more this is true. Unless you have a freebore that is ~.0005" larger than what is common(usually about .0001-.0002" bigger than typical bullet diameter), you are not actually getting to the lands without pushing really hard.
Different bullet brands/models will give different comparitor measurements due to bullet diameter and ogive shape. A longer taper will allow you to push farther into the freebore than a more rounded ogive.

 

[General RE LEE]

Update:

Cleaned rifle and measurements were normal. Actually found about 30 thousandths throat wear on 6.5 Creedmoor (1500 rounds)