Case Confusion

[0-tolerance]

Hello LRH community,

I just broke in my 300 RUM and I am trying to figure out why my fired cases base to shoulder number is smaller than the virgin brass. Using a headspace comparator, the virgin brass starts out as 2.467 and the fired cases end up as 2.456. I am so confused as to why this is happening. Has this happened to anyone else or know why this is happening?

Thanks!

 

[dfanonymous]

So, just to clarify, YOU are hand loading this ammo correct? Also is the bolt hard to close?

Because with just that info, it sounds like the virgin brass hasn't been full length resized. Your brass is firing forming to your chamber. Which is why it's the size it is. That would be an amateur mistake.

If you ARE indeed FL resizing, perhaps you're die might not be set up correctly. Unless the bolt is closing easily…

 

[0-tolerance]

The bolt closes fine. I full length sized all the brass prior to loading and measured it at 2.467. Correction, the fired case is 2.465, not 2.456.

 

[DJ Fergus]

How much does your case diameter below the shoulder grow upon firing?

 

[0-tolerance]

How much does your case diameter below the shoulder grow upon firing?

.006

 

[P7M13]

Measure virgin. (2.467)
Measure FL Sized
Measure fired case. (2.465)
Please post the third number
Doesn't seem to be an issue to me.

 

[0-tolerance]

neck -
Loaded .336
Fired .345

 

[DJ Fergus]

Did you measure your virgin case before or after running it through your sizing die. Typically a sizing die will many times bump the shoulder of a virgin case down even farther if you set the die up the way many die manufacturers say to set it up.

 

[0-tolerance]

Did you measure your virgin case before or after running it through your sizing die. Typically a sizing die will many times bump the shoulder of a virgin case down even farther if you set the die up the way many die manufacturers say to set it up.

I measured it after sizing. That's just a habit I have as I got screwed once from not sizing virgin brass.

 

[DJ Fergus]

Are you running a mild load? Maybe just enough pressure there for the case to expand radially & shorten length but not enough pressure to increase headspace of the case on just one firing. Im just guessing that if you took one case and fired it 3-4 times with the same load, then you would see length at the shoulder increase.

 

[0-tolerance]

Are you running a mild load? Maybe just enough pressure there for the case to expand radially & shorten length but not enough pressure to increase headspace of the case on just one firing. Im just guessing that if you took one case and fired it 3-4 times with the same load, then you would see length at the shoulder increase.

I was kinda thinking that but just not sure. I'll anneal do another round and update.

Thanx all!

 

[fmuguira]

Kinda like F/L sizing a case and the base to shoulder length grows slightly UNTIL you continue to screw the die down and start getting more shoulder bump.

That brass is "pliable" and can go in different directions until a certain point is reached.

 

[can1010]

this is normal remember the case comparator measures on the shoulder and even the smallest difference in shoulder angle between virgin and fired brass will show up in this measurement.
nothing to worry about

 

[SSgt G Cody]

Sounds fairly normal to me! After 2-3 firings, brass should improve noticably!