M die expanding plug questions

[Char-Gar]

I am thinking about turning some expanding plugs for my various Lyman M dies and have two questions.

1. How much smaller than the bullet size do you want the expander plug?

2. What is thread size of the hole that screws onto the die stem?

Thanks for any help you can give me.

[1hole]

It sounds as tho you do have multipule M dies. Have you considered taking measurements from them and using that as a guide for what you will be turning? And checking the threads of the plugs?

[jaguarxk120]

Are the Mdies 7/8-14 or from the tong tool. The tong tool uses a odd thread size on the expander plug. somewhere between 30,31,32,33,34 thds/inch. If you have the 7/8-14 die just check the adjustment stem with your thread gauges.

[mtnman31]

Thread size for the plugs is 10-32 if I recall correctly.
As for size you're best bet is to do what 1hole suggests and use that as a starting point. I tried going with standard sizes on a few ans was very unhappy with the results. For what it is worth, I have made three different plugs for my 9mm Mak. For some reason I just can't get that one right. The Lyman one was too long and bottomed out on the web of the case, squishing it in the process. I trimmed it back and while it wasn't bottoming out, it was still ballooning out the case about half-way down. I just need to get back at it and play with the size.

BTW - If you do BPCR, you can easily make yourself some compression dies using the M-Die body and threaded piece. Just turn a flat plug and put in in place of the M-Die's normal expanding plug.

[Doc Highwall]

Make the M-die .001" smaller the the size of your bullets. If you size your bullet .310" then make the M-die .309" with a step about .003" to .004" larger for starting the bullet and will give you about .001" neck tension.

[Calamity Jake]

What Doc said, I make all my "M" die expanders .001-.002 under boolit dia.

[Char-Gar]

thanks guys for your help

[Buckshot]

.............Making an M die caseneck expander, and assuming you do not have collets and are using a 3 jaw chuck. You'll need to make a fixture to hold the mouth expander, and you'll need to grind a RH cutting tool having about a 0.100" radius cutting edge.

1) Chuck up a piece of 1" long x 0.500" steel. Face it off and centerdrill.

2) Mark it to the #1 jaw of the chuck so it can be replaced exactly each time.

3) D&T 10-32, countersink the edge of the taped hole well.

4) You've now made the fixture for your chuck to hold the expander. Set it aside for the moment.

5) You now need to grind a RH cutting tool with a cutting edge having about a 0.100" radius. You'll use this tool for making ALL subsequent expanders.

6) For the expander cut a piece of .500" OD High carbon steel (so it can be hardened) about 1" long. Chuck it with about 0.5" extending beyond the jaws. Turn down for about .375"length to .187" OD using the above made turning bit. Then thread it 10-32 tpi. Remove from the chuck.

NOTE* There are 2 reasons for the radius on the cutting tool. One is so when turning down the stock to create the .187" stem for threading you create a nice fillit on the stem at the base of the expander. This radiused fillit lends strength to the stem. The fillit is also the reason for placing a countersink on the taped hole in the fixture. You'll want the expander blank to thread up snugly against the face of the fixture.

The second reason is when cutting the expander itself you create a radiused step between OD's and finally a place to bump the casemouth to apply a bit of flare to the casemouth if desired.

7) Install the fixture you made previously back into the chuck (indexed to jaw #1).

8) Screw the casemouth expander in the fixture. When you start the lathe the taped hole in the fixture will run true (if indexed). The expander blank will not be true on it's major OD, but the threaded stem of the expander blank WILL be.

9) Since the expander blank is not running true (to one degree or another) and since it's held only by it's threaded shank, use good judgement on your DOC for the first cleanup passes. It shouldn't take much to have the OD running true.

The whole reason for the fixture we made was to have a piece we can remove and replace time after time in the 3 jaw chuck and have it's taped hole run true. This way with the stem of the expander also running true, when the expander is finished it's OD will also be true to it's threaded stem.

10) Since the fixture OD is 0.5" and so is the expander blank, it's obvious you'll be turning down some off the fixture as the bit clears the end of the expander blank. No problem. Turn the expander body down to about .470".

11) We're going to make the expander for a .452" pistol slug. We have a .470" OD at the moment and it will be the basis we work from. Dial in to remove metal leaving us with OD of .455" or so. We want to have a thousandth or a bit less for polishing down to .454". Also, stop about 0.100" short of the top of the expander body. We'll now have a .455" OD with a radiused transition to a .470" step and this is the part that will give us a casemouth flare if we want one, by bumping the casemouth against it.

12) Our expander is now .455" OD for maybe a distance of 0.400" and then steps up to .470". The .455" part we'll polish down to .454" when we're done and this will be the area the .452" OD boolit will initially guide into, so it doesn't need to be too long. Dial in to give an OD of .452" and turn lengthwise stopping to leave about 0.100" or a bit less of the .455" step.

13) Put a generous radius or taper on the nose of the expander. Now you'll need to polish the expander. If you use silicone carbide paper be sure to use oil. If you use a Cratex wheel be sure to cover the lathe ways well, and clean them well after polishing.

14) When hardening, leave the expander in the fixture so the threaded stem remains soft.

............Buckshot