Will a K&M Mandrel fit in 21st Cen Expander Die Body

[Dimner]

I have a 21st century expander die body. I'm thinking about buying the K&M neck turning system. I have read and agree that buying the expansion mandrel from the neck turner mfg is the best way to go.

Can I use the K&M neck expansion mandrel in the 21st Century Expansion die body?

If it helps some, 21st century has the following in the description of their mandrels.

21st Century Expander Mandrels and Arbors are designed for proper fit in our die bodies. While these may work in most Sinclair and PMA die bodies we cannot guarantee proper fitment in those bodies.

So I'm thinking if a K&M expansion mandrel works in the sinclair or PMA die bodies, then it would work with 21 century. But I have no clue if it does.

 

[358WCF]

A K&M .30 cal. expander I have measures .313" in diameter where it goes into the die body. This diameter is about .697" long.

 

[muleystalker]

I know the K&M expander mandrel I just recently purchased uses a different die body, the mandrel attaches to the Mandrel holder by a screw and then the mandrel holder screws into the top of their die body.
The 21st Century expander mandrels I have measured .375" diameter at the top of the mandrel, the K&M expander mandrels I have measure .3115" in diameter and won't work in my 21st Century or my Sinclair die body. I can say this I much prefer the K&M Expander body, it has holes through the body so you can see while setting up the die and you don't smash/collapse a neck and ruin the piece of brass. The mandrel holder also has index marks on top and each mark is about .005" when screwed up or down. Here are some photos of the 21st. Century arbor and K&M Arbor, them photos of the K&M set up.

For what it's worth I have the 21st Century Power Neck Turning Lathe and it works great, might want to check it out. 21st Century also makes an Arbor adapter so you can use a K&M carbide turning arbor, with a carbide cutter for cutting out the donut, on the 21st Century Neck turning lathe. I will use this for making .30 BR cases and for making my 6x.204 brass out of .204 Ruger cases. And when I was researching this I found the target difference in diameters between the Neck turning expander mandrels and the Neck Turning Arbors from 21st Century and K&M were the same. The K&M mandrels I have are the Original V1 and the
Powerstroke V2, if they made some before these 2 that were similar to the 21st Century I do not know but give them a call they are very helpful as are the people at 21st Century.

 

[Dimner]

Thank you so much for the detailed responses and measurements.

I did consider the 21st century lathe, but it just seems like I would be spending an extra cash on the lathe frame and lathe setup without really that much increase in performance over the K&M. Also, I love the fact that, with the K&M, I can spend under a hundred bucks and buy an extra neck turner body and cutter and leave it set up. Not sure if I will ever do that, but I like having the option.

I measured my 21stCen 30 cal mandrel that fits my 21stCen die, and it's 0.375 at the top just like muley's. Not the end of the world. Just means I have to spend a bit under $50 to get the right expander die setup or I guess go with the nitride 21cen expander mandrel. No idea if nitride is as good as keeping cool as carbide.

I do like 21cen tools a bit better than K&M. Some of the K&M stuff makes my head dizzy. For example, this graphic on which neck expander setup to choose:

 

[muleystalker]

Thank you so much for the detailed responses and measurements.

I did consider the 21st century lathe, but it just seems like I would be spending an extra cash on the lathe frame and lathe setup without really that much increase in performance over the K&M. Also, I love the fact that, with the K&M, I can spend under a hundred bucks and buy an extra neck turner body and cutter and leave it set up. Not sure if I will ever do that, but I like having the option.

I measured my 21stCen 30 cal mandrel that fits my 21stCen die, and it's 0.375 at the top just like muley's. Not the end of the world. Just means I have to spend a bit under $50 to get the right expander die setup or I guess go with the nitride 21cen expander mandrel. No idea if nitride is as good as keeping cool as carbide.

I do like 21cen tools a bit better than K&M. Some of the K&M stuff makes my head dizzy. For example, this graphic on which neck expander setup to choose:

View attachment 1524241

I'm pretty sure K&M is probably phasing out the V1 style and moving to the Powerstroke V2, the good thing is you can still use the V1 mandrels in the V2 system. As far as the Dice body or(Press adapter as they cal it) in standard 7/8" there are only 2 sizes to choose from, the shoe or long just like 21st Century offers.

21st Century also sell extra neck Turing heads with your choice or angle cutter for $119.00 or you can get it with a mandrel adapter, a K&M mandrel adapter , or with mandrel also or the body by its self. It looks like they changed their website around and it's a little harder to find. It's listed under the "ALL PRODUCTS" heading. just something to think about. I do think the 21st Century Turning heads have the most precise and easiest adjustment systems that I have fooled with. Thats what I did, I have heads for different cartridges and leave them set up for my most used cartridges, but I do change them every now and then when I need to do some other cartridges not used as much and the adjustment is painless and easy to set back to the previous settings.