Lyman M Die

Not open for further replies.


Jul 31, 2008
Are the Lyman M Dies better for cast bullets? I have read they are great for such bullets, but I always like to hear real world experience from other folks.

Using my current expanding die, it appears that the bullet doesn't always seat straight due to the round belling on the case. As the bullet is seated it becomes undersized and un-round by the time it reaches seating depth. I have pulled several bullets from un-crimped cases to verify that a sized, lubed and round .452 bullet becomes a swaggered down and un-round .450/.451 bullet. Also noted from Lyman, the M die's plug works deeper in the case than other dies which looks to be possibly more of the issue than the round belling. I had set my current expanding die to flare the case enough to just have the base a bullet fit in the case and did test with seating depth. I found that the further I seated the softer bullets the worse things became. I see this more in the 45 auto as I cast my bullets softer at about 11-13 bhn. Having a bullet undersized is a huge problem for accuracy and leading which are actually very much interrelated.

Any opinions on the Lyman M Dies?
I also like and use the Lyman M die, but in rifle calibers. What you need is the case neck being a thousandth or two smaller than your cast bullet, so the neck will firmly hold the bullet.

For a given rifle, the cast bullets I seat are .002" to .004" larger than the jacketed bullets the size die makers assume I am going to seat.
Lyman "M" die

This die will help you start your bullet straighter, but will do nothing to stop the sized case from sizing your soft bullets smaller in diameter. The expander and the "M" die both will only open the case to about .450" You need to make your bullets harder. I have used the "M" in rifles loading cast bullets, they are needed for a rifle.
The Lyman Neck-Expanding “M” die expands and flares case mouths
to facilitate bullet seating. Cast bullet reloaders
should use this die to prevent “shaving” of bullet metal during the seating
This die is identified by the “NECK EXPAND”
stamped between the knurled top and threaded shank of the die body.
The first step of this plug
expands the neck to slightly under bullet diameter while the second
step expands the first 1/16" of the neck to slightly over bullet diameter.
This allows cast bullets to enter the case without shaving lead.
"Are the Lyman M Dies better for cast bullets?"

The M expander is as good as advertised. And also excellant for jacketed stuff too, in both handgun and rifle, it aids straight bullet entry. I use one for every cartridge I load.
Undersize bullet

I have pulled several bullets from un-crimped cases to verify that a sized, lubed and round .452 bullet becomes a swaggered down and un-round .450/.451 bullet.
Other thing can cause this. Using a Lee factory crimp die. Another is setting your taper crimp die down to far. Try turning your bullet seat plug all the way down in the die and seat a bullet. Then pull the bullet and measure it. See if that makes a difference.
I crimp in another stage and do not use a lee factory crimp die. There as been no crimp at all prior to pulling the bullets.
The M dies work very well for lead bullets, and reduce the working of the brass for jacketed bullets.

They tried cost cutting a few years ago and using an aluminum shaft with a steel plug that screwed into the aluminum.

The aluminum was not hard enough and stripped out after a few hundred rounds.

When I called they sent a new shaft that was all steel.
Not open for further replies.