Bullet "jump" and Base to Ogive

@N @newton 7 months ago

When I have been measuring COAL (Cartridge overall Length) I have realised that that is not the most important dimension
Bullet manufacturers will (sometimes) supply the length of the bullet
However what is really important is the dimension / length at which the ogive starts
After all it is at the ogive ( full diameter ) that the bullet meets the rifling
and
This is where you measure "bullet-jump"
This is generally measured by ...BoT = Base to Ogive to give an indication of where the bullet will actually start engraving.
I am not sure if this information is provided - in a QL .bul file ?
I have discovered that I can actually load very long bullets ( as long as they fit in the magazine ) because a large part of the front of the bullet is NOT at ogive dimension - and my barrel / chamber has a long throat
This means that I can increase the load ratio without necessarily adding more powder ( pressure )

IF this information is supplied I would like to know where you find it ?
Rather than having to measure all the bullets manually

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@N @newton OP

Bullet base to ogive is not a constant value for bullets.
All that said, if so inclined, ask your gunsmith to make an insert using the reamer he used to cut your chamber using the offcut barrel piece left over. This will give you the most accurate tool for your rifle.

Thank you
Most helpful and valuable information

@J @janfred

Bullet base to ogive is not a constant value for bullets.

For best results you want to measure the value from where the ogive touches the lands. The angle of this area of the ogive is so close parallel to the bearing surface it makes it difficult to measure and very dependant on finger pressure. Couple this to the fact that the bullet dies wear over time, you end up where the bto value changes for every lot, becoming longer every batch until the dies are replaced.

The commercial measuring devices that you connect to your calliper does not measure at the contact point; which add to your variables. Better to have one made.

The contact point also changes depending in he lead angle cut by the chamber reamer. This angle can vary from +-0.75 degree to as much as 3.25 degrees.

To make matters less clear, the lead wears away over time and changes its geometry. It can start at 3 degrees and wear to 1.5 degrees over time.

All that said, if so inclined, ask your gunsmith to make an insert using the reamer he used to cut your chamber using the offcut barrel piece left over. This will give you the most accurate tool for your rifle.

@D @ds-j

This makes sense but I think you might be a step ahead of the industry.