Neck turning mandrel fit

R

rain164845

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What sort of difference do you shoot for between the expander and turning mandrel? What kind of fit do you get on the turning mandrel? I just got a set and the manufacturer indicated that a loose fit was intentional. The expander is about 1.5 thousandths larger than the turning mandrel. The issue is that the turner will cut a different depth depending on how it is held.
Thoughts?
 
You want a very, very, light slip fit. If the fit is too loose the case neck all will not be the same thickness all around.

If on the first expansion stroke the fit is too tight, make one or two more strokes with the expander. This sometimes picks up a slight amount.

Case neck turning for benchrest accuracy is all about each case neck being exactly the same within a case lot.
i.e. Don't try to finish a large bunch then lump them together. For example, turn a lot of, say, 15, put them in a case box, number the box, then do another case lot. Number them something logical like A17, B17, C17. etc.

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This is fairly important! You really need a slip fit as Jerry said. The turner will heat up if the fit is too tight and if you don't handle a loose fit mandrel properly the results are the same. Given the two choices, I'd rather have a loose fitting mandrel. Get a tight fitting expander mandrel and sand it down (drill and sandpaper) until it just fits.

That said, I've never been able to tell the difference in perfect cases versus close cases on the target. Yes, there's a difference at the loading table but none on the target. If you can't get past this, or don't agree, then see the above paragraph.

There's something relatively new I think. Folks are cutting chambers such that you don't have to turn the necks at all. I don't know what I'm talking about here so I'll leave it at that...just sayin'.
 
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Turning observations

Sometime in the last couple of years I bought 100 Lapua .223 Remington brass and 100 Nosler brass, same caliber. I just got around to measuring the neck thickness on each batch. The Lapua brass varied no more than .001" around the circumference, and most less than that, while the Nosler brass varied as much as .003" or more. I won't touch the Lapua brass, but I'll be turning the Nosler.

I also measured some BHA .308 match brass and that was as good as the Lapua. I also spot checked a bunch of Remchester brass in .260 and .30-06 and most of that was within .0015".

I'm no expert, but when faced with tight neck chambers on my 6 PPC and 30 BR I went with K&M expander mandrels and their window riser accessory. They were a good match with my Forster hand-held neck turner and mandrels. I used Imperial Sizing Wax as lube for both expansion and turning. I found fit to be just right in both operations. In both operations I relubed the mandrel every third case.
 
Turners

I tend to prefer no turn necks, but this particular one isn't a standardized cartridge, so I wanted to be able to try different brands.
My previous neck turner worked great with the expander ball in a die and was a somewhat snug fit. I could turn the case at 24 rpm with an oiled mandrel and we getting good results.
 
I re-read your initial post and believe your expander is too large for the neck turner. Put it in a drill and sand it to fit....easy does it until you get it right and "right" is a matter of how much the cases spring back from lot to lot.
 
rain164845 said:
What sort of difference do you shoot for between the expander and turning mandrel? What kind of fit do you get on the turning mandrel? I just got a set and the manufacturer indicated that a loose fit was intentional. The expander is about 1.5 thousandths larger than the turning mandrel. The issue is that the turner will cut a different depth depending on how it is held.
Thoughts?
Click to expand...

That sounds a bit large. I have four brands of turners and I measured the turning mandrels and expanders a couple of years ago and my notes say the difference are as follow

Pumpkin .0009
K&M .0012
21st Century .00105
PMA .00065

That PMA sounds a little tight, I better check it again.
 
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