Friends-

Refresh my memory for determing the correct bushing size for neck sizing bushings?

For example, you take the caliber and add to that (neck wall thickness times 2) and then I think you subtract .001 or .002 for neck tension.

Therefore, using a .264 Mag for example you would have the following if you had a neck wall thickness of .015:
.264 Bullet Diameter
.030 Neck wall thickness (.015 X2)
.294 sub-total
(.002) subtraction for neck tension
.292 Bushing size ???

Question is, what's the correct deduction for neck tension?

Thanks in advance.

We have discussed this quite a few times in the past, so a search will unearth more info. But just to recap:

1) the easiest and most reliable way of measure case wall thickness is to measure the neck diameter of a loaded round (then subtract bullet diameter and divide with two, if you absolutely must know wall thickness).

2) From loaded neck diameter, subtract as many thousands as you think you will need for neck tension - this will be your bushing size. Redding suggests a tension of .001" to minimize runout issues. I have found myself using quite a bit more than that to deal with inconsistent neck tension - due to unturned necks and brass work hardening over time etc etc. For target-type cartridges, I typically use .002-.003". For hunting type cartridges, .003-.004" has worked for me.

3) it is an illusion to think you can only buy one bushing size. Everybody always ends up with several. First, to experiment with what will work for your load/gun, secondly, to deal with different brass material (thickness, hardness etc).

4) Depending on the hardness of your brass, you have to figure about .0005 - .001" brass springback after sizing. Add this to your tension (i.e subtract this extra value to get bushing size).

- mike

Cartridge case necks vary in thickness form brand to brand and lot to lot. They probably vary a good bit within some lots.
The most fool proof way to get the right diameter is measure 25 or 30 loaded rounds about 3 places each and then use the smallest reading. You will learn a lot about your brass this way.
The measurement must be done with a good micrometer using good technique. A good micrometer means one that will meet the Federal standards for accuracy and precision. You should be able to depend on it to repeat to ±.0001. That is 4 decimal places.
If you have neither of these you need to acquire them.

Mike and Ireload-

Hey, thanks for the refresher.

Mike, you were correct, I was too timid with the search function.

Ireload, your comments were dead on. I outside turn necks on three different cartridges so, I have plenty of good mic's as well as ball mic's.

Most of all, thanks for your guidance on neck tension.