Mandrel as last step?

First time ever communicating here. Been shooting for the last 6 yrs. and getting better because of LRH. Started reloading 3 yrs ago.
I have only been a member for a short while and I love the available info I receive here.
When we do the math for applying the desired neck tension to a resized case (neck wall thickness, ID bushing size, & mandrel size) can the neck tension be confirmed by using a caliper? If so can the 0.0005" spring back be seen in the caliper measurement?
 
It depends on your caliper and your familiarity with using calipers to get precise measurements. The feel can be tricky at best, and hard to confirm .0005" (1/2 of one thousands of an inch) micrometers are much more precise, but specialized and costly. Gage pins can be gotten in an array of sizes. I recommend getting gage pins from .002 under the desired size to .002 over the desired size in .0005 increments. These pins can be had for $3-$5 each. They are round and on size, when you insert one in a case if it is primed there will be a slight pressure and when pulled out a suction if you are within .0005" and the next size pin does not fit.
Calipers are quick but not necessarily accurate to .0005"
 
I ordered a mandrel and gage pin from K&M to give .002 neck tension. I looked in my reloading notes and saw where I had tried this once before about 5 years ago and for the CM I was reloading it produced better, consistent loads. Thanks for all the feedback, I will be using mandrel as last step.
 
I've been a member of the site for a few years but don't really post much. I know this is an older thread but like the OP, i have questions about expander mandrels.

Let's take my 280 Ackley for example. Loaded ammo measures .310, so I am currently using a .308 bushing. If I wanted to achieve .002 neck tension would I get a smaller bushing, say .306 and then run it through a .282 mandrel?

Does it really matter which I use first, the bushing or the mandrel?

Help me out please.
 
Clbrooks,
The general procedure is to use your neck bushing first to squeeze the neck dia down, then follow with the mandrel to push any neck wall thickness variations to the outside of the case neck while achieving desired neck tension. Most use a little lubricant with mandrels. Graphite probably most common. Enjoy.
 
It has often been said that a mandrel will "push any neck wall thickness variations to the outside". Well, if you use a bushing die (no mandrel) to achieve .002" neck interference, and then seat your bullet: doesn't the bullet push any neck wall thickness variations to the outside?
 
It has often been said that a mandrel will "push any neck wall thickness variations to the outside". Well, if you use a bushing die (no mandrel) to achieve .002" neck interference, and then seat your bullet: doesn't the bullet push any neck wall thickness variations to the outside?
If I understand your statement correctly..... I do not agree....
you either have concentric neck o.d or concentric i.d. each ideally will be the same......
But usually not..... that is why neck turning is done, to make neck thickness the same 360*.....
 
If I understand your statement correctly..... I do not agree....
you either have concentric neck o.d or concentric i.d. each ideally will be the same......
But usually not..... that is why neck turning is done, to make neck thickness the same 360*.....

You may have not understood my question.

What is the difference between pushing the neck wall variations to the outside with a mandrel or the bullet itself?
 
Mandrel expansion should be seen as a pre-seating action.
It does push most thickness variance outward -away from seating bullets. With this, bullets seat straighter.
Pre-seating expansion itself is needed to bias residual springback energy inward, against bullet bearing.
Otherwise, if last sizing energy is inward, then brass will eventually reach lowest energy level by counter expanding outward, away from bullet bearing. This, reducing tension over time.

We should always size necks outward last, before seating bullets. And truly we should not be upsizing necks with bullet seating.
Bullets ARE NOT neck sizers.
Bullet seating should expand necks no more than normal elastic limit (springback range), which is not actual upsizing/yielding.
For tension adjustments, we should adjust sizing length on necks, and not interference.
 
Mandrel ID neck sizing is best for all the reasons mentioned above. Also, case deformation in the shoulder resulting in runout happens when pulling an expander ball out through the neck, especially when not properly lubricated. The neck / shoulder better resists the forces of mandrel expanding into the neck. Neck turning is a good thing to do when done correctly, but is not particularly necessary when mandrel sizing for a normal chamber. However, on a tighter chamber (in the neck area) neck turning is necessary.
But even with all of this, consistent neck tension is difficult to obtain with different hardnesses in the brass being used producing different amounts of spring back, and tension. Anealing is the next step the neck tension quest. It is very frustrating when you are not able to obtain consistent neck ID'S due to varying spring back.
 
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