Neck sizing trouble

[jeeptim]

This is my first attempt at neck sizing working with a brit 303 and a lee neck sizer ran about 100 primed added some powder put the case on the shell holder put my bullet in the case mouth and it fell right in checked the rest same deal the bullet dia is .312 case mouth 314 to .315 any ideas where Im
screwing pooch.
Thanx

 

[rcmodel]

IMO: By using Lee neck sizing dies.

There are a zillion threads here about over-size mandrels, thin case necks, etc.

It seems to be a common problem with them.
And an ingenious solution to a problem that wasn't with other brands of neck sizing dies.

rc

 

[flashhole]

I assume you have the Lee Collet Neck Die. Did you measure the mandrel in the die? It should be sized to give you .002" neck tension when you use it to size a case. Did you anneal the case neck and shoulder? It may help your situation but it sounds to me like you are not putting enough pressure on the mandrel. Lean on the press handle a bit harder and see what you get. What kind of press are you using?

 

[rsrocket1]

Install the die into the press, take the top off of the sizing die, take the mandrel and cylinder out and put a case into the shell holder to see how the sizing action works. If there is something stuck in the slots, they can't close fully. Take a set of calipers and measure the mandrel. If it is .314 or .315, that's the problem.

Also, did you screw in the die at least 1 full turn after touching the plate? It doesn't matter how much further because you only need to press with about 25 pounds to squeeze the neck against the mandrel.

 

[Scimmia]

IMO: By using Lee neck sizing dies.

There are a zillion threads here about over-size mandrels, thin case necks, etc.

Um, yeah. The "over-sized mandrels" are usually either improperly adjusted dies or overly work hardened brass. Thin case necks won't really affect the die at all. How about this, $10 says it's an improperly adjusted die or improper use in this case.

 

[kingmt]

I would suggest backing the die out some to get more press with less pressure. I actually have mine adjusted so the press bumps over very easily.