Measuring Die Neck Diameter without Pin Gauges?

[DrSteve]

I contacted RCBS recently because I couldn't find any published specs on their full-length sizing die neck diameters. They were kind enough to provide the following info:

6.5 Creedmoor .283 +- .002"
270 Winchester .298 +- .002"
7mm-08 .303 +- .002"

I was surprised RCBS does not hold them to tighter tolerances. I want to try using them without an expander and a .004" swing could make a significant difference on neck tension. There is a set of pin gauges on Amazon for $120, but that's alot of $$$ for an old retired guy. I know Forster will hone to tight tolerances, but I already have these RCBS dies.

I have a caliper and a ball micrometer, but no inside micrometer.

I thought maybe I could size brass without the expander ball and subtract .001" for springback. Would that give me a close estimate of the die's neck diameter?

 

[Mikecr]

If you want a specific neck interference you can get a bushing die.
Otherwise it don't matter, because there is nothing you can do about whatever it is, other than sending the die off to be customized.

 

[DrSteve]

If you want a specific neck interference you can get a bushing die.
Otherwise it don't matter, because there is nothing you can do about whatever it is, other than sending the die off to be customized.

I agree with you about not being able to change the diameter without lapping, but knowing the precise diameter would still let me know what the tension would be for different thicknesses of brass, and the stock RCBS die might coincidentally happen to be a good match "as-is" for one type of brass or another. For example, my 6.5 Creedmoor Remington brass measures .012" neck thickness and my Lapua measures .014". Using Forster's die honing recommendations, if the RCBS die is at their max diameter tolerance (.285"), it's a good fit (loaded round -.003") for using on my Remington brass without an expander ball. If it's right on spec (.283), it's a good fit (loaded round -.005") for using on Remington brass with an expander.

 

[marchboom]

You could get a set of ball-type small hole gauges to measure the neck portion of the die. That would give you a good starting point. But it just might be better to get a Forster die and have it honed to what you need. Forster FL dies are great for keeping runout very low. Better than any other die I have used.

 

[ButterBean]

You can get pin gages from MSC for abot 5 bucks a pop

 

[DrSteve]

Thanks for your comment, I could get four gauges for each of the three calibers I currently load for $60 plus shipping, or a big set on Amazon for $120 with free shipping that would cover just about everything. Still wish there was a cheaper way.

 

[DUSTY NOGGIN]

size without expander button in die , measure
size with expander button in die , measure difference
seat a bullet in an unturned brass , measure difference

start neck turning , turn a little off at a time until you meet your your desired tension with expander stem/ button the die

if you end up turning too much off and its stick thicker than .012... , your gonna have to buy a bushing die

 

[LM056]

Pin gages also available at: https://vermontgage.com/gaging-products/standard-pin-gages-and-sets

 

[DrSteve]

size without expander button in die , measure
size with expander button in die , measure difference
seat a bullet in an unturned brass , measure difference

start neck turning , turn a little off at a time until you meet your your desired tension with expander stem/ button the die

if you end up turning too much off and its stick thicker than .012... , your gonna have to buy a bushing die

Thanks you.

 

[DrSteve]

Pin gages also available at: https://vermontgage.com/gaging-products/standard-pin-gages-and-sets

I'll check it out. Thank you.

 

[ButterBean]

size without expander button in die , measure
size with expander button in die , measure difference
seat a bullet in an unturned brass , measure difference

start neck turning , turn a little off at a time until you meet your your desired tension with expander stem/ button the die

if you end up turning too much off and its stick thicker than .012... , your gonna have to buy a bushing die

I don't think that will change your neck tension (ID Interference) all that will change is the OD measurement

 

[MagnumManiac]

I over honed my RCBS 338WM dies neck.
It is .001" under bullet diameter...it doesn't matter because I use a mandrel as my final step.
Honing a die is a simple step in a lathe.

Cheers.

 

[DUSTY NOGGIN]

I don't think that will change your neck tension (ID Interference) all that will change is the OD measurement

you are right . expander button is the limiting factor ..

but benefits are still good you will be equalizing tension and the expander button or mandrell sizing upon the openening rather than bushing down sizing . while not having to buy a different die

 

[redneckdan]

Use cerrosafe to make a casting of the neck area. Use modeling clay to plug the top of the die. Follow the directions for dimensional stability.