Seating Die Diameters

[wv109323]

For straight walled cases, what should the clearance be between the seating die and the resized case?
I occasionally get a round that does not pass the plunk test. I experimented with different seating stems and with some the reject rate was 50%
I am loading a 120g.powder coated boolit into 9mm cases. Bullet size is .3570. My dies have a lot of tolerance when seating. With the RN stem the problem is seldom but I tried the SWC stem and the problem of boolit run out was a lot worse.
I am now using a .38 spec. Seating die to help the problem.

[fc60]

Greetings,

It may be a specific brand of brass. Does the problem persist with all loaded rounds?

Some brass have thicker case walls and a 0.357" bullet may be too large for that combination.

Cheers,

Dave

[wv109323]

I have not noticed a specific brand of brass doing it. I think it is more related to the alignment of the boolit while setting it on the case. The stem does not match the bullet profile. With Dillon dies there is only 2 seating stems available, RN OR SWC.
I have measured several cases and they are pretty close to being the same thickness. But their hardness or strength may vary causing the brass to deform or buckle.

[243winxb]

"causing the brass to deform or buckle." Crimping while seating is the cause. The 9mm seat die inside diameter is to small, for your fat bullets.

Bullet alignment, on seating, is helped by an "M" type expander.
https://www.thehighroad.org/index.php?media/rcbs-expander-m-type-9mm-strange-black-coating.3604/full

[Mk42gunner]

I've never measured a seating die, although I have measured the crimp occasionally.

You may be trying to crimp too much, causing the slight buckling of the cases. There is a reason everyone recommends trimming brass to the same length for a standardized crimp. That said, almost no one trims 9mm brass.

Robert

[Winger Ed.]

You might have a longer case than the die is set for sneak in there and it collapses on the crimp stage.

If you will use a separate taper crimp die, it has more toleration for different case lengths,
and that should at least minimize that happening if not eliminate it.

If you're using one die to seat and crimp on one stroke-
it's almost impossible to avoid crushing a few unless you measure and sort all the cases for length.