View Full Version : A few comments about TRIM dies - case forming and sizing only

03-13-2015, 02:29 AM
These comments are in regard to dies used for sizing and forming cases. (The Lee case trimming dies are a different application)

All the differences between these dies and FL size dies are not well documented - even by the factories

Most of the RCBS trim dies that I own follow this pattern.

1. The neck ID is about .010 larger than the corresponding RCBS FL or neck die necks. (all from .17 Ackley Improved Bee @ .198 to the .38-55@ .394 have the .010 larger neck diameter.)
2. The head to gauge dimension is the same as a FL die.
3. The die sizes the case body to about the same dimensions as a FL die. I have not measured all of these die body dimensions.
4. I have two trim dies for the 6.5X53R Dutch. One is the size of a FL die in the body. The other is a little larger in diameter but the brass still chambers using this die.

The 3 Redding trim dies (not much of a sample I know)

1. 30-20 REdding (.32-20 used with .308 bullets)

32-20 Cowboy


30-20 Redding


30-20 Redding


2. .40-65 Win This is a modern die about 15 year old and the neck is the same as a sizer for the .406 bullet version of the .40-65 at .416 in the neck. If the brass is .010 per side this leaves the sized neck at .396. This is way too small for a trim die when using .408 to .420 bullets.

3. 7.92X33 Kurz (this is the short 8mm for the StG 44)
This neck dia is

7.92x33 Kurz


Where there are a variety of sizing die options, brass thicknesses, chambers and bullet diameters you may find an application where the .010 over size trim die neck is just right.

There are several different brass thicknesses available for the .38-55 and .375 Win. The bullets vary quite a lot too.

The groove diameters of the .38-55 may be all over the place.

You might benefit from sizing .0075 thick Starline brass in a RCBS .38-55 die. This die has an neck inside diameter of .394. .394 - (2 x .0075) = .379 Just right for a .380 bullet and not much expansion for a .381 either.

If you have a .375 Win here is what you get with .010 thick .375 Win brass.

.394 - (2 x .010) = .374 Just right for a .375 bullet in a single shot.

03-15-2015, 12:49 AM
So you can probably run a case through the trim die, and then get a neck turner pilot into the resulting case neck without further fooling around?

03-15-2015, 01:32 AM
Not a good idea.
The only way to get the inside of a neck just right for holding .0001 wall thickness is to use an expander that is sized just right for the neck turner pilot.

If you have an expander you can make the pilot to fit.
If you have the pilot you can make an expander to fit.
When properly expanded the case neck inside diameter is a line to line fit with no clearance on the expander. So tight there is no wobble, so tight it needs lubrication to prevent galling, but not so tight that you cannot easily turn it.

If you need both you or if you cannot make the expanders and pilots you can buy them from K&M or some benchrest supply place like Sinclair's or Bruno's.

This is K&Ms offering http://www.kmshooting.com/catalog/case-neck-expanding-tools/expand-iron_complete.html

Forster pilots http://www.forsterproducts.com/index.asp?category=22490

So you can probably run a case through the trim die, and then get a neck turner pilot into the resulting case neck without further fooling around?