Mandrel as last step?

Cornholeo

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Been using Redding type S bushing dies on 3 rifles for awhile with great results but have seen in different forums people removing the the expander ball and using a mandrel as last step. So if you use a mandrel as a last step, wouldn't that throw off your desired neck tension?
As an example, I have a .310 bushing to use on my upcoming 7SS using ADG brass for desired neck tension. If I get a K&M .284 mandrel does that throw off my desired and planned neck tension established with the bushing?

School me on this please and thanks in advance!
 

Rardoin

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You can get your final neck size, or tension if you will, by either a bushing to the exact OD or with a conventional FL/NS or bushing that undersizes and then expand it outward with a mandrel to your final size. They both work. As Greg mentioned mandrels are available in many 'under sizes' for a given caliber. For my 7mm I have them from -0.001" to -0.0030 in 0.0005" increments (K&M). This allows testing many different diameters to see what your gun likes. The same can be accomplished with bushings. Which is better? Honestly I have tested both processes of arriving at a final neck diameter extensively in a 6.5 Creedmoor, 6.5 x55 BJAI and .284 Win and the two methods are equivocal in my hands as judged by test targets at 600 and 965yds. I have heard claims of less runout with mandrels but I assure you, if I am not using proper dies, a good press, and technique I can get plenty of runout with either method.....or under 0.002" TIR with either with proper tools/technique.
 

GatorTrapper

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you can also get mandrels from NOE.

I use no expanders in Redding dies just use their method to select bushings.

Buy Nosler brass and 1/2 moa groups are no problem.

Big game is big. The distance you can shoot a 10" group in real world field conditions is where you stop.

Small groups are 10% of being a successful hunter.
 

Mikecr

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Groups (small or large) mean nothing to hunting.
In contrast, cold bore ACCURACY is the most powerful of ballistic attributes.

But my input on neck sizing: interference fit is not tension.
We do not set tension with mandrels.
 

cajun

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Groups (small or large) mean nothing to hunting.
In contrast, cold bore ACCURACY is the most powerful of ballistic attributes.

But my input on neck sizing: interference fit is not tension.
We do not set tension with mandrels.
Well I guess most of the top F class shooters who use mandrels and bushing dies would be surprised to hear that. I’m not sure what you call it matters but turning the necks to a consistent thickness, annealing brass to a consistent state and setting the amount of sizing you do to the neck are pretty much the extent of the variables a reloader can control. If I’m missing something please enlighten me.
 

Mram10us

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Groups (small or large) mean nothing to hunting.
In contrast, cold bore ACCURACY is the most powerful of ballistic attributes.

But my input on neck sizing: interference fit is not tension.
We do not set tension with mandrels.
Group size sure matters to me :) it seems my cold bore shots are closer together when I've been able to get my group size lower. Please explain the point you're trying to get across, because I'm really not understanding what this has to do with the OP's question.
 

Mikecr

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I'll try an analogy.
While tightening a connection fastener (a bolt), and you reach a point where turning force no longer goes up.
Is it a good idea to continue turning?
Does it make a stronger connection to stretch the bolt shank well passed it's yielding point?
Answers: No, and No
I'm sure most here have experienced this in their lifetime. You just know you're screwed right there, and hoping with all you got that you can get the bolt back out (to replace it) without the head snapping off..

A common bolt connection is in proper tension while it's bolt shank has stretched, but not so far as to yield. When you loosen such a connection the bolt recovers it's form and can be re-used.
Where you go beyond this, the bolt yields, the tension it provides is not going up much, or at all, or is going down, and it will never recover it's form.

Back to reloading.
When you seat bullet bearing into excess interference fit, you cause neck brass yielding(up sizing). While there is high frictional forces required to do this work, the tension that grips the bullet (squeeze force) is not going up. And when you then pull that bullet, you find that the neck does not recover. It only springs back ~1/2thou,, it's normal amount, even if you had overcome fully 5thou of excess interference.
All you're doing with that is over-working the neck brass, while gaining no 'extra' tension.

To understand the futility in this you need to understand that bullets are not pushed out of necks on firing. Friction means nothing in this.
Instead, bullets are released from necks by their expansion, and even a relative few molecules worth of expansion fully frees the bullet.
That firing expansion is resisted by the neck's springback force times the area of bearing that force is gripping (PSI). Doesn't take much.

If pressure did have to overcome neck friction, internal ballistics would be completely different than it is.
In fact, if you were to force this, let's say by having zero neck clearance(not interference, but truly zero clearance), your gun would explode.
That is, unless you greatly reduced the friction to prevent this(so much so that your bullets would never hold set seating depths).
On our scale of things, including timing, it's hard to picture but very real. And you can test it & prove it (without dying).

Ideal mandrel use is a 'pre-seating' operation.
The mandrel would be at cal/bullet diameter. It would perform any neck upsizing so that your bullets don't have to (they're terrible expanders).
When you remove the mandrel the neck will spring back (inward) ~1/2thou, ready for actual bullet seating.
There is no difference in this from what you already do with your bullets.
To adjust your tension go to FORCE X AREA [pounds of force per square inch].
Adjust the LENGTH of downsizing to spring back against bearing (with that force of springback).
 

Mikecr

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Group size sure matters to me :) it seems my cold bore shots are closer together when I've been able to get my group size lower. Please explain the point you're trying to get across, because I'm really not understanding what this has to do with the OP's question.
I was replying to an earlier declaration that: Small groups are 10% of being a successful hunter.
And I replied to OPs concern about mandrel sizing.

As far as PRECISION (grouping) -vs- ACCURACY (hitting your mark) they are totally different.
Your cold bore shots may be 'closer' with a hot grouping load, but still be unacceptable for long range hunting.
A great hunting load can be terrible for grouping.
What matters is what you need.
 
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