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A collection of comments and articles on the many aspects of bullet casting by various cast bullet shooters
Cast Bullets For Beginner And Expert
SECOND EDITION, 2007 - Joe Brennan
A Table Of Lyman "M" dies

Norm Johnson

     The "M" die expands the case as usual, then puts a small step which is a couple thousandths over nominal bullet diameter at the very mouth of the case, allowing for straight and true bullet starting.

     A few years ago I purchased a dozen "M" die expander plugs from Lyman to use when I need an over-size or special diameter plug. These I have a machinist friend turn down for special experiments.

     They do, however, come in a great variety of sizes from Lyman if you do not have access to a lathe or machinist's services. They are listed below.

     (The plug screws into the top thing. The top thing screws into the expander body. The hip bone... Note that expander bodies

The Plug

 come in two lengths. M1 is long (left), M2 is short (right). You can purchase various dimension plugs from Lyman. You can buy untold quantities of stuff from Lyman, they never seem to complain. If you have a long, or M1 expander body, you won't be able to expand short cases. I bought a 7MM "M" die, that came with a long or M1 expander body. When I tried to expand 7MM TCU cases, I found that even after screwing the top thing all the way down, I couldn't get the case far enough into the die to expand it. This led to confusion. A call to Lyman cleared the whole thing up. I needed a SPECIAL 7MM TCU "M" DIE. I bought it, and could then expand the 7MM TCU cases. You can expand long cases in the short M2 expander body. So if you have one = 1 short M2 expander body, you can screw any plug into the top thing, screw the top thing into the short M2 expander body; and expand away. joe b.)

M" Die dimensions from Lyman
Diameters +.0000/-.0005
Rifle First Second
Plugs Step Step Bullet sizes
22R .222 .225 .222


24R .242 .246 .243


25R .255 .259 .256


26R .262 .266 .263


27R .276 .280 .277


28R .282 .286 .283


30R .307 .311 .308


31R .310 .314 .311


31AR .318 .322 .319


32R .320 .324 .321


33R .337 .341 .338


35R .357 .361 .358


37R .374 .378 .375


45R .455 .459 .456


M" Die dimensions from Lyman
  Diameters +.0000/-.0005  
Pistol First Second    
Plugs Step Step Bullet sizes
25AP .249 .253 .251 --
30P .307 .311 .308


32AP .310 .314 .311


32P .313 .317 .314


38AP .353 .357 .354


38P .356 .360 .357


10MM .398 .402 .399


10MM .408 .412 .409


44MP .427 .431 .428


45AP .450 .454 .451


45P .453 .457 .454



Rifle Calibers


"M1" and "M2" Expander Die Bodies:

Use With:




17 Rem x  
22 Hornet x  
22-250 Rem   x
220 Swift   x
222 Rem x  
222 Rem Mag x  
223 Rem x  
243 Win   x
6mm Rem   x
25-20 x  
25-06   x
250 Sav.   x
257 Roberts   x
6.5 x 55   x

Rifle Calibers

"M1" and "M2" Expander Die Bodies:

Use With:

  M1 M2
7.62 x 39 x  
32-20 x  
303 Brit.   x
32 Win Spc. x  
8mm x 57   x
8mm Rem Mag   x
338 Win Mag   x
35 Rem x  
358 Win   x
35 Whelen   x
375 H & H   x
38-55   x
444 Marlin   x
45-70   x

"M1" and "M2" Expander


"M1" and "M2" Expander Die Bodies:

Use With:

  M1 M2
270 Win   x
270 Win   x
7-30 Waters   x
7mm Weath. Mag   x
7mm Rem Mag   x
7mm x 57   x
280 Rem   x
30 MI x  
30-30 Win x  
300 Savage x  
308 Win   x
30-06   x
300 Win Mag   x
300  Weath M   x

     How are these dimensions related to the 'steps' above?

The main shaft of the expander portion is the "First Step". It is typically a few thousandths smaller than bullet diameter, as are conventional expander buttons.

     The "Second Step" puts a small step of increased radius in the case mouth about 1/16th inch deep (adjustable). This step is a few thousandths over bullet diameter to aid effortless starting.

     What are expander bodies?

     The die bodies that hold the expander plugs; directly analogous with conventional expander dies.

See the Lyman catalog (or above) for a picture which is worth a thousand words.

     How much expansion or bell does the M plug put on the case mouth?
Ideally, for lead bullets, the first step would be about .002" under bullet diameter. For jacketed bullets, the first step should be .003-.004" under bullet diameter. In either instance, the second step will be 2, 3, or 4 thousandths over bullet diameter.

     Usually the best lead bullet diameter is about .0005" less than the chamber's measured throat. Most of my .30 caliber rifles shoot .310" or .311" cast bullets best. I keep several plugs on hand and have a machinist friend turn them to my specs if I think it will help.

     It is also highly desirable, on a two diameter rifle bullet, for the nose of the bullet to be of bore riding diameter. To check this for a given bullet, push the bullet nose first into the rifle's muzzle. If it goes in without resistance, the bullet nose is too small and good accuracy is not as likely.

     Does the seating die crimp out the bell or do you just leave the cases expanded? Your choice. For my
lever actions I Sometimes crimp. For bolt actions, I do not.



Warning: All technical data mentioned, especially handloading and bullet casting, reflect the limited experience of individuals using specific tools, products, equipment and components under specific conditions and circumstances not necessarily reported in the article or on this web site and over which The Los Angeles Silhouette Club (LASC), this web site or the author has no control. The above has no control over the condition of your firearms or your methods, components, tools, techniques or circumstances and disclaims all and any responsibility for any person using any data mentioned.

Always consult recognized reloading manuals.


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