Bullet Jump

[boats1]

In lay terms, please explain "bullet jump". Thanks.

[Jonathan Doe]

Bullet jump is generally understood as the distance that the bullet leaves the cartridge mouth where it is seated, to where it engages the rifling. Usually, the shorter the bullet travels brfore it engages the rifling, it is more accurate. I ususlly seat my bullets ~.005" - .010" from the rifling and they show good acuracy. However, if your bullet touches the rifling when you chamber, then you run risk of higher pressure.

[bcrich]

Bullet jump is the amount of travel the bullet has to make before making contact with the rifling. Some rifles shoot more accurate with very little jump such as bolt guns but with auto's you can only load as long as your mag length. Assuming you reload try playing with your seating depths and see what your gun prefers.....but you don't want to get right up on the rifling cause that can also cause high pressures

[boats1]

Thank you. I understand.

[CSACANNONEER]

There are some bullets that are designed to be seated to a depth which allows them to touch the lands. These are called "boreriders" and they are safe to shoot when there is zero bullet jump. But, this is a special case! As far as the whole accuracy thing goes, I'm not totally sold on the conventional wisdom that you have to have minimal jump to produce both accurate and percission groups. Thanks to the fine attorneries at Armalite, my AR50 came with so much freebore that I can not seat a bullet out far enough to be within 1/2" of the lands! I still can make it consistantly shoot .5moa to 1.5moa. The larger groups are due to my mistakes/misreading conditions rather than the gun.

[ar15barrels]

There are some bullets that are designed to be seated to a depth which allows them to touch the lands. These are called "boreriders" and they are safe to shoot when there is zero bullet jump. But, this is a special case! As far as the whole accuracy thing goes, I'm not totally sold on the conventional wisdom that you have to have minimal jump to produce both accurate and percission groups. Thanks to the fine attorneries at Armalite, my AR50 came with so much freebore that I can not seat a bullet out far enough to be within 1/2" of the lands! I still can make it consistantly shoot .5moa to 1.5moa. The larger groups are due to my mistakes/misreading conditions rather than the gun.

I'm of the opinion that the throat diameter and alignment is a larger factor in accuracy than the bullet jump length.
If you have a long and loose throat, the bullet gets out of alignment before it hits the rifling.
If you have a long throat, but it's a tight fit to the bullet and centered in the bore, the bullet moves straight into the rifling.
A shorter, tight and centered throat is the best.
A short but crooked throat will probably never shoot well.