Expanding mandrel & neck turning mandrel differences?

[Jmccracken1214]

I ordered a mandrel and wanted to get .002 neck tension, so I ordered what I thought was an expanding mandrel, but happened to be a NT mandrel and is still .002 under bullet diamter...

It looks the same, so Im assuming it is the same and I am safe to go ahead and use this as a "expanding mandrel"?

 

[whatsupdoc]

Difference is NT mandrel is .001 smaller than expander mandrel.
I use the NT mandrel it works.

 

[Jmccracken1214]

Difference is NT mandrel is .001 smaller than expander mandrel.
I use the NT mandrel it works.

Awesome. I figured but wanted to make sure the shape or something crazy wasnt slightly different before I went to town on the brass.

 

[Lawnboi]

I’d even say preferred over an expanding mandrel. If your goal is .002 tension, the spring back of a .001 under mandrel usually leaves me Atleast with around .001 to .0015 tension.

 

[Baron23]

Difference is NT mandrel is .001 smaller than expander mandrel.
I use the NT mandrel it works.

Ah, respectfully...I do not think this is necessarily so.

Yes, a lot of mandrels described as being NT are .001 under caliber diameter but not all expander mandrels are .002 under. In fact there are kits out there (21st Century Innovation, for example) where you get a set of expanders in .0005 which I have found to be very useful in getting a pretty dang exact I.D. of the neck which is dependent on the brand of brass (and its neck thickness), how work hardened it is, how it was/was not annealed and who knows what else. With this kit, I can find the mandrel that gives me that .002" (or interference fit of your choice) confirmed by pin gauges after expansion.

Caliber Specific Expander Mandrel Kits

Our caliber specific expander mandrels are available in .0005” increments in calibers 22 to 338 and will range from .001” above bullet diameter to at least .003” below bullet diameter depending on caliber. This will allow the reloader to find proper neck tension to fine-tune their loads. The...

21stcenturyinnovation.com

I've never understood just buying some company's .002" under mandrel and then just expecting (without confirmation) that you are actually getting the interference fit dimension you actually want.

Here is PMA (good company, make nice stuff) sold by Benchrite who show an "NT" mandrel model as being .002" under

PMA Tool Stainless Steel Neck Turning Mandrel

These excellent stainless neck turning mandrels from PMA Tool are machined from 17-4 medical grade stainless steel.

benchrite.com

And here is another one from PMA (carbide) what doesn't say (but I'd bet it was .001 under) AND note that it doesn't have a tapered end which I kind of associate with NT vice expander

33 cal. Carbide Neck Turning Mandrel

neck turning pilot

www.pmatool.com

They really aren't much/any different (well, except some NT don't have a tapered end and I would not use in a press to expand).

Cheers

 

[spife7980]

^Wrong for a good part of it

As they came originally with the intention of turning case necks an expander mandrel is .001 under bullet diameter and the turning arbor is .002 under bullet diameter (or .001 under expander as mentioned above) so that the case neck is just ever so slightly larger than the turning arbor and provides a tie fit to ensure the necks are getting cut uniformly.

Now that the people are using them for other things you need to know why you’re buying.

I use the turning arbors of .002 below caliber for my general case prep mandrel.