Neck tension - looking at it the wrong way?

[VA_XTC_Shooter]

Why would the bullet seal against the forcing cone, it's larger in diameter the the bullet.

No it's not, the bullet is squeezed here into the lands and grooves and seals.this is where the engraving pressure occurs.

 

[Straightshooter1]

Probably some of both. But the neck definatelly opens before the bullet is completely out of it.

Agree that the neck opens before the bullet is completely out. My point in my post was that the bullet "begins" to move first, however minute, before the neck begins to expand . . . if the force it takes to expand the neck is greater than the force it takes to move the bullet. Unless there's some other force involved, like a crimp, the bullet will always start to move, a very small amount, before the neck starts to expand. . . or unless something like 30-60 lbs. of pressure can actually expand the neck first . . . which I doubt, unless something like the neck being fully annealed where it doesn't take much pressure to do so. I can think of an easy physics experiment, if one has the tools, to actually see this by pressurizing the cartridge from the base and measuring the neck and bullet's movement as the pressure increases. Certainly, if the bullet is touching or jammed in the lands, that's a whole different scenario.

 

[46and2]

We need a ultra high speed camera, a clear polymer chamber, colored powder inside of a case with a bullet seated, pressurized with compressed air.

The sine wave we see on the case neck is a sign.

I miss the Mythbusters!!!