Mandrel Size

[Gmac]

I know how to get size of bushing for outside of neck. I don't know what the formula is for finding mandrel for inside diameter. Any formula help for figuring the mandrel size would be greatly appreciated. I'm sure that I am over thinking.

I go .003 allowing for .001 spring back netting me.002

Is this for your mandrel selection?

A neck that has been worked down by the die and then worked back up by a mandrel would have to be sized to .001" of bullet diameter to allow a spring back of .001" and net .002" of clearance, no?

If your bullet diameter was .264" and your die worked your brass back down to a .254 inside dimension you would have .010 of "interference fit" with the .264 bullet. If you used a mandrel that was .003" under bullet diameter and accounted for .001" of spring-back, the inside of the neck would have a difference of .004".

If you were trying to achieve .002" of "interference fit" between inside neck and bullet diameter, wouldn't you have to use a mandrel that was .001" below caliber and account for you're anticipated .001 of spring back?

 

[QuietTexan]

A neck that has been worked down by the die and then worked back up by a mandrel would have to be sized to .001" of bullet diameter to allow a spring back of .001" and net .002" of clearance, no?

This is the theory, yes. The reality is that it depends on the hardness of the neck and variations in thickness of the neck.

Some people anneal every time to keep the hardness consistent. Some people change bushing and/or mandrel size as the necks harden. Some don't care and use the same everything all the way through.

 

[Mike Matteson]

I would really think that you would need to see, what the spring back is either using bushing, or mandrels. Then you'll see what the spring back is. So depending on which system you are using, will require bushing or mandrels. If you haven't turned your necks, Then the mandrel would be my choices. Depending on what or how much tension you want by using a different size. At the same time if your neck are cut, then bushing dies will work to achieve the same thing. What I don't see much about is annealing the brass. That changes how stiff the brass is, or pliable the brass is and that changes after each firing of the case. How much I don't know. You can see what differences it makes by reloading your cases, and suing them again. Keep track of the grouping each time, and see what happens. It probable won't be much at first, but after several firing there should be a notable change in grouping. Each have away of approaching on how they reload.

 

[Gmac]

Condition of the brass is definitely going to influence the affects of either resizing with bushings, buttons or mandrels. I stayed away from the annealing conversation purposely to keep it simple and not further derail the thread. My point was in the the math (using stated .001" spring back) regarding how to end up at the stated .002" net "interference fit" in the prior post .... it was backwards.

 

[Mike Matteson]

You are going to the trouble of setting tension on the neck. Your cases will last longer by annealing. You don't have to do it every time, but it's better.
The other problem is neck thickness are some different between each case. Some more and some less. So you will have size you neck to smaller than caliber size for sure. Just what is need I can't give you that. The mandrel will push out the uneven portions of the neck to the outside to seat the bullet and that better. So it's kind of a guessing game. Like stated above you will need to go under .003 or .004, then expand back out again to get your neck tension.
It to me, you don't want to do the work to really get into items that really should be done to get your better grouping cut down your ED & SE down. You don't have too, but. You are trying to use mandrels to set neck tension, (a good thing) and figuring that enough. You'll have to get some different mandrels O.D. dimension and try them out to see which one you need. You will be at some point in time, and looking back saying: Wish I had done, what I am doing now, and taken a little more time to do it, to start with.
You would better off cutting all your neck for thickness to a set dimension to start with. then get the correct bushing to size to the dimension you want. Different manufactures of brass are different. That why most everybody states enough brass of one lot to do the job.
Reloading can be 2 ways. It's either fun to create a better load for your rifle (s), and hit what you are aiming at, or just get close and call it good.
Some trail and error in which mandrel is going to be the ticket.