Whoa there. What the heck is up with this?

[updatelee]

considering the neck is deformed I would guess they are now shorter and after you fireform them they will go back to their long length, so trim after you fire them as well.

new brass is terrible for length, on a package of 50 winchester brass I have some that dont touch the cut head, and others that I grind so much off I check the length with a caliper to confirm my trimmer isnt out of whack.

 

[sunray]

"...what causes it to do that?..." Your sizer die is down too far. The bottom of the die should just kiss the top of the shell holder with the ram all the way up.

 

['Boo]

Depending on the type of resizing die you have......remove decapping stem and resize loaded round, and Bob's you're uncle!

And unless he owns a dedicated body sizing die he could spend the rest of the day trying to remove a loaded cartridge that is thoroughly stuck in the neck portion of the die.

 

['Boo]

pharaoh

Pull the bullets and dump the powder back into the jug.

Take the decapper pin out of the expander rod and re-size the cases leaving the primers in place.

Trim them all to minimum length and chamfer the case mouth.

Re-charge the cases with a minimum powder load.

Set up you seating die making sure the crimping ring is not contacting the case mouth before the bullet is fully seated.

Seat the cheapest bullets you have.

Go to the range and fire-form the cases while practicing off-hand shooting.

 

[adriel]

As most have said, the crimp operation is causing your brass to buckle. Different lengths of brass run through the same crimp die will result in varied crimps: light, medium, heavy, and buckled cases. This is one of the reasons that having a LEE factory crimp is nice, because it uses a collet to crimp and will not buckle the case.