funky neck measurements?

[queen_stick]

Alright guys, this one has me a stumped.

This is with 6.5-284 brass...
I turned some brass to .013' neck wall thickness. Then sized the necks to an outside diameter of .290', giving me an inside diameter of .263' = .001' neck tension. All is well until I get to one piece of brass where the outside is .290' and the inside is .264',.001' larger than the rest of the cases). Using my RCBS ball mic,with 10thou readings), the thickness of the neck on this case is .0128... I get this reading consistently, and remeasured it way too many times, and also rotated the case many of times while measuring.

So, the question here is how does 2 10thou's neck wall thickness equal a full one thou larger inside neck diameter, when compared to the rest of that cases?

I know worrying about something like this is ridiculous... that's why I'm not worried about it; I just won't use that case. But I'm curious why this is???

Also, when turning necks, do you really need to worry about .0002' difference? If so, then every chamber I get done in the future will be a no-turn!

Thanks,

Walt

 

[mikecr]

Not sure how you're measuring ID on these..

If I understand correctly, you turn unsized,beyond normal mandrel expansion) brass to .013 thickness. Times 2 is .026 and +.264 = .290,again, unsized). You then neck size for .001 tension which would mean sizing with a .288 bushing allowing for the .001 of springback.

Perhaps the oddball measured just took to the neck sizing a bit different because of it's annealing or material. It's close enough provided tension is inline with the others, which might be moreso after fireforming.

Just throwing out the only thing that comes to mind at the moment.

 

[queen_stick]

Thanks for the reply Mike. I was thinking about the brass properties too... The brass could use annealing. The spring-back when neck sizing is right on .001. I'm using a 289 bushing, and getting a finished .290 neck.,.290 -,.013x2) = 264). If I'm measuring 263 inside, then I must be doing something wrong. What that 'something' is, I'm doing it consistently, because get the same result every time.

I'm measuring ID with my caliper... just using the inside blades, stuck in the case mouth. Is that not a good way to measure the ID of the neck? I must be doing something wrong in measuring the ID?

 

[alf]

I'm measuring ID with my caliper... just using the inside blades, stuck in the case mouth. Is that not a good way to measure the ID of the neck?

No, same as using them to measure the outside diameter. Might as well use a ruler.

 

[queen_stick]

alf,

If I'm not supposed to use a caliper to measure ID or OD, then what should I be using?

 

[tightneck]

alf,

If I'm not supposed to use a caliper to measure ID or OD, then what should I be using?

Why are you measuring the ID of your necks in the first place???

 

[alf]

alf,

If I'm not supposed to use a caliper to measure ID or OD, then what should I be using?

Why are you measuring the ID of your necks in the first place???

Zackly.

Everyone that shoots a tight necked chamber needs a ball mike,which you have) and a regular 1' mike. Then you can measure bullet diameters, loaded case diameters, etc. ACCURATELY!

Calipers are good for case lengths, bullet lengths, OAL's, etc.

 

[queen_stick]

Alf:

You're saying I should measure OD with a ball mic? Then to figure out ID, simply subtract the neck thickness from the OD? (I'm not new to reloading, but I am new to precision reloading, and there are obviously some things I'm not aware of). I figured simply measuring the ID was an easy way to figure out the actual ID.

Walt

 

[janderson0]

You use the ball mic to measure the neck wall.

What others are triing to say:

1- A caliper is not a good tool for neck inside dia.
2- you do not need to know what the inside neck dia is.

Jim

 

[queen_stick]

Interesting. I won't be measuring the ID any more. Thanks guys!

Let's say I need need to measure the ID of something. What would be the tool to use for such a task. (I'm no machinist, nor do I have experience in "precision measuring," but like learning about the subject).

 

[janderson0]

I know my gun smith has a box with a series of pins in it. I think they are called pin gauges. You find the largest that will fit the hole. I know if I try to use a caliper that the measurement will vary as to how you hold or technique.

 

[coues52]

new guy here,anyway check "larrywillis.com" Innovative technologies he has some great tools and a real good tech site,worth reading.I just bought his " Digital Headspace guage and Belted magnum collect resizing die" but read his tech tips.~Danny

 

[Klong]

Queen_Stick one thing you can do with the tools you have, is measure a bullet diameter, seat it in the case in question and then measure the outside case neck. Do the same thing with a bullet of the same diameter and one of the other cases to see if the outside neck diameter of the cases are different. If all the numbers are the same, then either your ID measuring is in error, your neck thickness measuring is in error or the brass has some different property allowing a different spring back after sizing.

 

[GermanS1]

Walt, if you're still looking for some information on this topic, go www.riflemansjournal.blogspot.com and in the October section I have an article on neck tension that covers what you need to know.

As others have mentioned, you need a ball micrometer to measure neck wall thickness and you need pin gauges or a very small inside micrometer to directly measure inside diamter but it isn't necessary to do so if you have an adequate proxy - like neck thickness and outside diameter.

 

[Bugs]

Trying to measure this stuff with a ball micrometer and calculate neck tension is a good approximation at best. Get yourself some "go" plug gauges from McMaster Carr in 0.0001" increments and you will know exactly how much tension you have.

 

[queen_stick]

Thanks everyone, for your thoughts and advice. I appreciate it.

German:
Thanks for the link. I'll definitely be reading that in the near future.

Bugs:
Do you use the plug gauges to measure neck tension? If so, does that method offer any advantage (decrease in group size) over simply using neck thickness and outside diameter?