You are one lucky sucker if you get an M die to work out of the box with the one stem (plug) included. I determine the diameter of my bullets for each firearm and then get the stem size ordered that I need. I suggest planning on special ordering from the manufacturer.

I use the expander plug (M die) when the brass is swaging down my bullet as I try to seat it in tight brass. I select the diameter of my bullets carefully and don't want the seating to change that.

So if you still have a problem after using the M die, you can change the "stem" of the expander plug by emailing the manufacturer and requesting a different size stem. I don't believe Lyman does that for their M die, but I know for certain that RCBS does.

Just talked to Lyman about the stem for the .45 ACP "M" die being too small for what I was doing. I need my cast bullet to stay .454 not .450
Lyman suggested and I ordered the 45-70 M die stem which is .456 stem/plug . So if after spring back takes the brass to .455, I may still need to polish a .001 off the stem to match my bullet size of .454.


You have to answer the question yourself, because we can't see what's happening. Pull a few bullets and check their diameter for swaging down the diameter. If your bullets are too small after pulling them and measuring, you need a larger stem for the expander.


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