Lyman "M" die question

[Steven66]

After reading about neck tension in the archives, I ordered a Lyman "M" die for .357 Magnum and have a couple of questions:

Are the plugs that come with the die usually enough to accommodate cast bullets as-is (I'm guessing a couple of thousandths over groove diameter?), or do you frequently have to have a custom plug made?

I'm shooting a fixed-chamber rifle. For practice loads, can I get away with just decapping and expanding the neck with the "M" die? I would of course resize cases for hunting loads to assure proper feeding.

[Taterhead]

I have a couple of Lyman M dies. Unfortunately I can't help with the dimensions of the 357 though. I can say that if it doesn't work out for you, the RCBS expander with the 38 Cowboy plug is correctly dimensioned for loading my .358" cast boolits. The RCBS expanders are now the M style too.

[Ed_Shot]

The M-Die "38P" expander plug for 38/357 expands the case neck to .356. I size my 38/357 boolits to .358 for both pistol and rifle. The 38P plug has always work for me. If you expand greater than .356 I'd worry about having enough neck tension.

[Larry Gibson]

What ever 357 dies your using should have come with and "M Die" type expander?

I've been loading 38/357 with Lyman and RCBS dies and with the propriety Dillon dies in my SDB for years. The standard expanders with each have done quite well with bullets sized .357 through .360. I normally size .357 or .358 for both cartridges with BHN 10 + cast PB bullets. With softer bullet of 30-1 or 40-1 I use GC'd bullets and the standard expanders work fine with those.

[EDG]

You can find dimensions for the Lyman M die plugs on this thread.
http://castboolits.gunloads.com/show...rements-Needed

[ascast]

just happen to have one here on the pile .356 step up to .359 marked 38P

[Gohon]

Maybe I'm reading it wrong but I get the impression the OP is talking about the expanded step the M-Die forms at the case mouth, not the expanded depth section of the brass.

[HangFireW8]

I have a couple of Lyman M dies. Unfortunately I can't help with the dimensions of the 357 though. I can say that if it doesn't work out for you, the RCBS expander with the 38 Cowboy plug is correctly dimensioned for loading my .358" cast boolits. The RCBS expanders are now the M style too.

IMHO too many of the Lyman M expanders expand to jacketed dimensions. For example the common .224 bore rifles, the M expands to .222". If you size boolits to 1 thou over bore that's .225" so you have .003" of squeeze, which is too much for plain base bullets. If you size to .003" that's 5 thou of squeeze. You can get away with ramming a gas checked case in there, but it will size down a plain based boolit.

For the American .308" bore you can use the 31R M expander, but if you have a loose Lee or Moison .311+ bore, then you're still too tight.

I am also not in love with the abruptness of the step on the M die. Measuring rifle case concentricity I've found hitting the step will often drive a concentric case .004-.005" out of square. That's not what I need for accuracy loads.

I have mostly given up on M and gone to NOE in a Lee expander die.

[reddog81]

I'm shooting a fixed-chamber rifle. For practice loads, can I get away with just decapping and expanding the neck with the "M" die? I would of course resize cases for hunting loads to assure proper feeding.

That will not work. If you do not resize the case, the bullet will usually just drop into the case without any resistance. Using the Lyman M expander die will have no effect as the case mouth is already too large.

[HangFireW8]

Wow I missed that last question.

Reddog81 is right.

Not neck sizing at all could only work soft seating and single loading, or with a very tight necked custom chamber. Some Schuetzen shooters do this but their guns are set up for it.

[gpidaho]

Steven66: I would recommend the NOE expansion die and plugs over the Lyman or RCBS. The function is the same but you can chose to the one one thousandth of an inch which size expansion plug you need for the just right fit of YOUR bullet. Gp

[mdi]

While the M die works quite well, I prefer a plain taper for my large cast bullets. If the M die had a bit more flare on the case mouth, I would like it better. My "normal" cast bullets (.358" for my 38s and 357s) the M die works well...

[Steven66]

What ever 357 dies your using should have come with and "M Die" type expander?

I'm using the standard Lee four die set for 38/.357 Magnum.

Thank you all! OK, I get that you have to resize to get neck tension, then flare the case mouth to accept the cast boolit (or any bullet), and I apologize for the obvious "duh" moment. Is precise neck tension (in x thousandths of an inch) more critical in bottleneck rifle cases than straight wall pistol cases? Perhaps I don't need a special expander die for cast bullets after all?

[stubshaft]

It is equally critical in either one. If the neck tension is too high it can size down the cast boolit. The easiest way that I have found to check is to load a round and use a kinetic boolit puller with a wad of cotton in the bottom of it. Measure the boolit after it has been loaded and pulled. It can be an eye opener...

[HangFireW8]

It is equally critical in either one. If the neck tension is too high it can size down the cast boolit. The easiest way that I have found to check is to load a round and use a kinetic boolit puller with a wad of cotton in the bottom of it. Measure the boolit after it has been loaded and pulled. It can be an eye opener...

I agree.

Neck tension can matter before the round is even fired. Feeding into the chamber can set the boolit back. If a magazine is loaded, boolits can be pulled out of cases from recoil (like a kinetic bullet puller), or smashed into cases in tubular magazines on recoil recovery by the magazine spring and the hammer of other cartridges.

Some slow ball powders require firm crimp for good ignition e.g. W296/H110.

For accurate rifle, consistent neck tension is good for accuracy.

Soft seating an work well with single loading, especially if the boolit engages the throat, keeping in mind the caveats listed above.

[kenyerian]

Steven66: I would recommend the NOE expansion die and plugs over the Lyman or RCBS. The function is the same but you can chose to the one one thousandth of an inch which size expansion plug you need for the just right fit of YOUR bullet. Gp

I like Noe's system also.

[Steven66]

What ever 357 dies your using should have come with and "M Die" type expander?

Thanks; I went back to Lee's Modern Reloading and re-read the section on their expanding die. The book claims that "You do not need so-called "M" dies that control the expansion...". I think I will just have to try and see how well the boolits seat and how the rifle shoots.

I like using the powder-through expanding die in conjunction with the auto-disc powder measure. If I wind up needing a customized expanding plug (hollow to allow powder through), I'm guessing I could modify the Lee plug, or does someone make custom hollow expanders that I can just buy?