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? about Lyman "M" dies

2764 Views 5 Replies 5 Participants Last post by  Big Bore
Novice with a few questions here so please bear with me as I'm sure that this is not rocket science to those of you who have been loading cast lead bullets for a while.

I was looking through my latest Midway-USA catalog and I saw their listings for the Lyman "M" dies. I can see that they list a "short" and "long" for certain calibers for cartridge cases less than 1.950" and more than 1.950" That would mean, as an example, that a .35 Remington case would require a "35 short" M die and a .356/.358 Winchester or .35 Whelen would require a "35 long" M die, correct?

I have noticed that some of these M dies seem to be caliber specific and in that case there is no need to be concerned about "short" or "long", correct?

Last of all, am I right to assume that these M dies are to be used after the cases have been re-sized, trimmed, chamfered and de-burred?

Thanks for the help. I'm trying to learn all that I can before diving head first into cast lead bullets in my rifles. So far, much of the other info I have obtained at BTB has kept me from making mistakes as I knew nothing about cast lead bullets before I found this site.
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M-Dies for cast bullet reloads

I use either the Lyman M-die or the equivalent RCBS product for case mouth flaring before seating lead bullets. This is necessary to prevent damage to the heel of the bullet and also to ensure that it gets started straight in the case.

Either type is fine, but you DO want to use one. It's also a help with flat-based jacketed bullets, which don't start into the case as easily as a boattail.
Dutch, I've got both short and long "M" die bodies. There is more overlap than the catalog would indicate, because there are at least two different lengths of the stem that the expander ball is mounted on.

There is also a 'widebody' die for the really fat cases, ie. .50-110 and the new short magnums but I don't have one of those.

Last, you may already own a die body that can be used for the really short stuff like handgun cases. The expander die in the current RCBS carbide die sets for handguns has the same threads for the stem as the Lyman "M" die bodies.

OK.... here is what I recommend. First, you will find these so useful that you might as well get a short and a long die body, either separately or as part of a caliber that you order. Then you should be set up for about any caliber, save the really fat ones as noted above. And again, if you have some RCBS handgun expander dies, you may be able to use them as die bodies for the "M" expanders.

Then..... when you add calibers just order new expander ball/seating stem combos, saves a few bucks. I'm not aware of any of the big catalog outfits selling these separately but you might find a well-stocked gunshop & be able to pick and choose.

There is some time spent in setting them up for different calibers, but what I did was lock the ring on the die body and never move it, then on the expander stems, I put a locknut on them to preserve the adjustment.

I'll try to take a picture of some of the different parts tonight, which I think will help explain your options better.

By the way these aren't just for cast bullets, they are just great for jacketed bullets as well.
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OK here's a picture of some "M" dies and parts.

Left to right, there are two 'long' die bodies, a 'short' die body (I think), two RCBS handgun expander die bodies which can be used, two (upsidedown) long stems (one with expander and one without), two short stems (also upside down),and some expander plugs.

As you can see, the main components are the die bodies, stems, and plugs, with locknuts to hold them in position, of course.

Rather than have a complete set for every caliber, I've chosen to have just a few die bodies and instead have more stems and expanders (others not shown). The reason for this is that I have two presses that I might use, and I have set up the longest and shortest dies bodies for a specific press. You might be able to read "RCBS" and "Dillon" written on the die bodies, which are the two presses I use.

The die body in the middle, the 'short' Lyman, is an extra and can be adjusted enough that it will work for either rifle or pistol, depending on the stem length. So it gets used for experimenting.

I set up a stem/expander combo for a cartridge, and use an extra lock nut so that the adjustment isn't lost between the presses. So it's pretty quick to set up and the stem/expander can go in the box with the rest of the usual die set, and if the right die body is used, can be switched between presses without having to be re-adjusted.

Adding a new caliber then only requires a stem of the right length, an expander, and perhaps an extra lock nut.

Since I can make the expander buttons and stems pretty easily - basic lathe work - it costs me nearly nothing to add new calibers. Of course this isn't true for everyone, but still, just buying the stem, expander, and locknut 'should' be cheaper than an entire new set.

If you only have one press then this might be overkill. If you only have a few calibers to reload then you might just set up an expander in a die body for each caliber, a small expense. But once you get your first "M" die, I predict you'll be getting them for the rest of the calibers you reload for, whether for cast or jacketed.

It's truly one of thos products that you wonder how you ever did without it, once you use it.
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Also, don't just think the M die is for lead bullets. Since I started using the M die to expand the necks after sizing (deprime with universal decap die, tumble, size with decap/expanding stem removed, then neck expand with the M die) I have found the need for trimming is greatly reduced with the same brass/primer/powder/bullet/load combination. The explanation is that when you use the normal expander button in the sizing die, as you withdraw the case from the die the expander pulls the neck larger and the case longer. With the M die, it expands the neck on the way in, not out, and does not stretch the case length. I've proved this time and time again, taking fired cases of equal length, sizing and expanding one normally, then sizing and expanding the other with the M die. Not alway, but most of the time you will see case expanded with the normal decap/expander button in place turn out to be .001 to .002 longer than the other case that was sized with the decap removed and expanded with the M die.
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