Am I gettin' Senile?

S

shinny

Shinny
A few days ago I made up some 30BR brass from Lapua 6BR. I necked it up in 3 stages then turned the necks to a very precise .0093.

Loaded with 34.7g of 4198 set the bullets .005 into the lands, lubed the neck shoulder junction w/Ballistol and fired.

I then neck sized it and when checking the dimensions found the Neck Thickness had grown to .0095-.0096.

This is not the first time I have noted this condition and was wonderingf if anyone else experienced this or am I getting Senile?:confused:
 
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Those tolerances are best kept in a controlled environment, if not a 68 degree lab. The temps here have changed dramatically over the last few days. Are you checking them inside where the temp is at least reasonably stable? These variables are often overlooked and when talking about a couple of ten thousandths, the tools we use are susceptible to change with temps. If you hold a mic too long, it'll warm and change slightly too.--Mike Ezell
 
Mike,

Thanx for the reply.

I do not hold the ball mic and to my best recollection the temps were reasonably the same. This expansion happened after the first fire forming.

Was at a shoot over the weekend and a few other shooters said they have experienced the same oddity.

Next time will try checking under very close conditions.

Shinny
 
Shinny, Brass cut at a true .0093 will never thicken to .0095 or .0096. Somewhere the turning tool has changed. Back when
turning necks became a standard thing, I made most of my own neck turners out of aluminum. They work but there are
things that need to be understood. The expansion ratio of aluminum is far greater than steel and changes around .0003
were commonplace just from hand temps. Within a year I made them from steel and have had no problems at all. No
ice water, nothing. The other item I would mention is the ball Micrometer,, it is very prone to user error. If your not
using a ball mic every day, the feel is hard to duplicate. I have been reading them for 40 years and will be the first to
admit that. A much better way is to measure a loaded round.
 
Hello,
I experienced too some days ago.
I found the edge of necks after shooting curved inside. If you resize your case you'll find the neck thickness .0093". It should be that your rifle chamber is not perfectly straight, so you could need a reamer for the rear part of chamber that could be conical.
 
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Elkhound said:
Hello,
I experienced too some days ago.
I found the edge of necks after shooting curved inside. If you resize your case you'll find the neck thickness .0093". It should be that your rifle chamber is not perfectly straight, so you could need a reamer for the rear part of chamber that could be conical.
Click to expand...

Be careful-sounds like your cases are actually too long for the chamber and you are getting a crimp at the mouth.
 
Jim Borden said:
Be careful-sounds like your cases are actually too long for the chamber and you are getting a crimp at the mouth.
Click to expand...

No Jim, that isn't the case..CL is 1.550; cases are 1.520±.

However, I did find the culprit. I have several 75w Flood lights shining on my work area. Seems I left the brass under one of this lights before measuring it. When I put in a unlit area for a while and re-easure all is OK, Duhhhh.:rolleyes:

Thanks 4 the input Jim. Hope all is well with you & Joan.

Shinny
 
Shinny

My comment was not about the problem you are having-I was addressing elkhound with his necks curled in at front!

Jim
 
Jim Borden said:
Be careful-sounds like your cases are actually too long for the chamber and you are getting a crimp at the mouth.
Click to expand...
Hi Jim.
This is the my first thought. Then I measured the chamber with a gage I built by a lathe and it measures 1.720". I trimmed to 1.695 so the chamber length is not the problem. As you can see from the pictures I was quite scrupulous in measuring. At the moment I didn't find a solution.
Shinny did you measure the neck after resizing?
straigthedgeafterresize.jpg

beforeresize.jpg

curvedadge.jpg

chambergage.jpg

afterresize.jpg

1720measure.jpg

For the next shooting session I'll try to trim the case to lower measure to verify if the problem remain or not.
Costa
 
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Elkhound said:
Hi Jim.
This is the my first thought. Then I measured the chamber with a gage I built by a lathe and it measures 1.720" so the chamber length is not the problem. As you can see from the pictures I was quite scrupulous in measuring. At the moment I didn't find a solution.
Click to expand...
Elkhound,
I am not sure what chambering you are talking but at 1.520" it certainly is not a 30BR . Case mouths crimping shut typically is case is too long for chamber as Jim says. Been there done that, at a Nationals match no less, and had to borrow a case trimmer.

What chambering are you talking about, the neck looks quite long?

Dick
 
Hi Dick,
I talk about my old Walther KKJ-E in 222R caliber. And the chamber is 1.720 as you can see from the pictures, not 1.520.
Thank you Jim for warning. Sure I'll check carefully case neck at the next shooting sessions and will trim the neck shorter to find out a solution.
Costa
 
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