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queen_stick
Reply with quote  #1 
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
Reply with quote  #2 
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
Reply with quote  #3 
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
Reply with quote  #4 
Quote:
Originally Posted by queen_stick
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
Reply with quote  #5 
alf,

If I'm not supposed to use a caliper to measure ID or OD, then what should I be using?
tightneck
Reply with quote  #6 
Quote:
Originally Posted by queen_stick
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
Reply with quote  #7 
Quote:
Originally Posted by tightneck
Quote:
Originally Posted by queen_stick
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.
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