Any reason not to use an M die?

[wtfooptimax200]

It seems that the m die is a popular option when loading boolits. Has anyone found any negatives associated with it? Is there a compelling reason NOT to use it? Thanks!

[Calamity Jake]

"M" Dies, one of the best case neck expanding tools made for loading boolits. You may need to buy custom size expanders
for odd size/oversize(.315-.316) boolits.
One short die body with different sizes of expanders usually is enough for most popular calibers.

[462]

They are the only expander die I use -- mostly with custom expander plugs -- and can't think of any reason why not to use them.

[geargnasher]

I can think of an excellent reason to modify them, but not to "not" use them. The issue for me is that the second step is always too big in relation to the first step, and the problem comes about when you set them deeply enough that the second, larger step on the spud expands the mouth beyond about .020 or so deep. Per the design, you punch the case mouth out so that a boolit can be seated parallel to the case, which usually requires .050-100" of the larger shank be plunged below the case mouth. When you do that, you ruin the neck tension at that point, which doesn't do well for building accurate ammunition. Lyman's concept is that the second step is just slightly larger than boolit diameter, so you can "start" the boolit a good way into the mouth with your fingers, and when seated, it will be forced straight. I've had nothing but trouble plowing open a case neck by using the boolit for an expander, which is in effect what happens with these, as the boolit must stretch the brass about five thousandths or so as it's seated, which usually causes something to get bent or compressed. By using a sizer and expander of proper shape and dimension, all this can be averted and the boolit can be eased into the case, achieving ideal tension for the length of the neck and nothing gets bent or distorted in the process.

My recommendation is to use a sizer die that doesn't size the neck too small (for example, typical .30-caliber dies size the neck ID to about .303-5" with the expander stem out, and if you're shooting a .311" boolit you only need to size it to .309" at the most), and either use an RCBS cast bullet expander die or turn down an oversized Lyman spud to make the first parallel section about a thousandth smaller than the size of the cast boolit to be used, then have a gentle flaring taper above that to start the boolit. If the boolit is only expanding the case a thousandth or maybe two after brass springback, it will go straight since that is the path of least resistance. Gentle application of roll crimp will restore the case mouth without losing any tension, and you can turn the mouth inward for more crimp of desired without having the bulge at the base of the crimp like can happen with factory M-dies due to the oversized second step.

I like to size the case to have an ID of about two thousandths smaller than the boolit, then expand to about 1.5 thousandths smaller than the boolit and give just enough of a "VLD" flare so that about 2/3 of a Hornady gas check will sit inside the case mouth. I also like the expander part to be a little longer than the case neck, have about a half-degree taper on the part inside the neck, and almost have a point on the end so it pilots gently going in. It's easy to correct the Lyman spuds to do just this by modifying with a drill press, file, and sandpaper, or in a pinch a handheld electric drill works fine. But you have to have something to work with, so check the sticky thread on M-die spud specs and get one that has enough meat on it to allow you to reshape it properly, and don't forget to modify your sizer die or change to a selectable-size neck-sizing die so you don't overwork your brass and possibly ruin neck concentricity.

Gear

[Doc Highwall]

I make all my expanders like the Lyman M Die. I like the part that expands the neck to be .001" to .002" Max smaller then my sized bullet, and the part for the case mouth flair to be .001" to .002" larger then my sized bullet. For example for my .310" sized bullet I make the expander .309" and the flair part .312".

[geargnasher]

Doc, you've tuned the spud to your needs, and it doesn't do too little/too much as the factory M-die spuds tend to do. Here's a copy/paste from the sticky here, and my experience with a few of them match these dimensions. Note the large difference between first step diameter, second step diameter, and suggested boolit diameter:

M" Die dimensions from Lyman

Diameters +.0000
-.0005

Rifle Plugs..First Step/Second Step..Bullet sizes

22R .222 / .225 .222-.226
24R .242 / .246 .243-.244
25R .255 / .259 .256-.257
26R .262 / .266 .263-.265
27R .276 / .280 .277-.279
28R .282 / .286 .283-.285
30R .307 / .311 .308-.310
31R .310 / .314 .311-.313
31AR .318 / .322 .319-.321
32R .320 / .324 .321-.323
33R .337 / .341 .338-.340
35R .357 / .361 .358-.360
37R .374 / .378 .375-.377
45R .455 / .459 .456-.458

Pistol Plugs

25AP .249 / .253 .251
30P .307 / .311 .308-.310
32AP .310 / .314 .311-.313
32P .313 / .317 .314-.316
38AP .353 / .357 .354-.356
38P .356 / .360 .357-.359
10mm .398 / .402 .399-.401
41MP .408 / .412 .409-.411
44MP .427 / .431 .428-.430
45AP .450 / .454 .451-.453
45P .453 / .457 .454-.456


As you can see, they're necesarily sort of "generic, designed to fit a range of cast boolit diameters. For pickier work, sometimes one must make custom plugs to match their boolits. The key is to have the expander expand enough, but not have a second step that is way too big and wipes out the neck tension for the depth it is inserted into the case.

Gear

[462]

Gear, I agree that the factory sized expander plugs are not designed for our usually fat-for-caliber cast boolits.

With that in mind, the custom made bottle neck plugs allow for .002" neck tension, while the second step is .001" over boolit diameter and 1/16" deep. For handgun cartridges, the first step is the same length as that of the boolit seated inside the case.

[Bent Ramrod]

The only time I found an "M" die not indicated with a cast boolit is when I use bore-diameter paper patched boolits. I had to make a non-expander plug for a fully resized case that only belled the mouth slightly.

The only other reason for not using them is if you have a specialty cast boolit benchrest rifle with neck-turned cases, custom dies and hand or arbor press seaters. Then you're beyond the "M" die class of shooter for sure.

[GOPHER SLAYER]

The thing I miss the most about being forced to sell my lathe is the fact that I can't make an "m" die anytime I want. The only reason I can think of for not using an "m' die with cast bullets is if you might be mentally impaired and I know there there are no such people who reside in this website.

[brassrat]

I resemble that and don't own a M die. I never get bullet shaving. Why don't they come in a die set?

[Doc Highwall]

M dies are a Lyman trade name that they make for shooting cast bullets that are larger then jacketed bullets. Straight wall cases already have a third die to flair the case mouth. Lyman offers them as a separate die for people who load cast bullets for bottle neck cases. The advantage of the M die is the two steps, the first one expands the inside of the case neck for the length of the case neck larger the a conventional expander would. The second step expands the case mouth too just over bullet diameter and allows you to do this without making the case mouth look like a hollyhock blossom if you go too deep.

[square butte]

Anyone that would be willing to offer an opinion and or rational as to length of the first step (smallest diameter) - to beginning of second step (larger diameter). How should this measurement/distance be calculated - or is it arbitrary/standard? Thinking of haveing a few made up for cast calibers. I've read the sticky and it looks like either .500 or .400 as kind of standard - Unless I am misreading it.

[oneokie]

For rifle cases, 0.500" would be sufficient. For pistol cases, the length should be equal to or slightly longer than the seated depth of the boolit.

[square butte]

So my guess is that .500 would be OK for bottle neck rifle cases - but probably not straight wall rifle cases like 45-70. Sounds like for straight wall cases the plugs need to be customized for different cast boolits. That's going to mean a bunch of plugs. Lots of molds in this household.

[Doc Highwall]

The small part has to be as long as the case neck plus .025"-.050" longer. The large part does not have to be much longer then .100", you only need enough to let half the gas check enter. For 30 caliber the 30-40 Krag has a neck length of .486" so add .025"-.050" to this and you will be able to use it for all 30 caliber cartridges that use the diameter bullet that it was made for.

[square butte]

Is there a strategy for limiting the number of plugs for straight wall cases? I must have 8 - 15 molds apiece for 38/357, .44 and .45 straight walls.

[geargnasher]

Is there a strategy for limiting the number of plugs for straight wall cases? I must have 8 - 15 molds apiece for 38/357, .44 and .45 straight walls.

Yes. Make or have made a straight expander only spud of the diameter you desire for boolit tension and long enough to handle your most deeply-seated boolit. Adjust depth per each application. Then you can use any of your existing expander/belling/M-spuds to open the case mouth per your preference (flare or step).

[square butte]

Thank you gear. 5th generation Texan here - currently displaced to new england.