Bump Sizing Once Fired Brass from 2 Different Rifles

BC Sportsman

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Feb 18, 2020
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New to reloading (but have done lots of loading using only new brass) so this is a real newbie question. I have 100 cases of once fired Gunwerks brass. Almost all were fired from my new rifle (300 Win Mag) but a few were fired from another rifle of the same caliber. Unfortunately, the cases are mixed together because I did not anticipate that I would be reloading the cases. I recently decided to "go green" and recycle and am regretting my lack of foresight.

How can I determine which case was fired in my older rifle so that I don't have to full length resize all of them? I'm thinking of measuring the headspace on each fired case as well as the case body diameter just in front of the belt and then separate them into the two groups by significant measurement differences. Will that work?

If I determine the max head space dimension for my new rifle using the "close the bolt on a new case with a partially seated fired primer" method and then set my sizing die to bump all my brass by 0.002" (after confirming that the bumped cases will chamber properly), then do I need to worry about whether the brass was once fired in another rifle? I just ordered a Forster Datum tool to do this measurement.

If my once fired brass in both by new and old rifles didn't expand enough to allow a 0.002" bump, then is it still safe to use them without bumping happening? I'm guessing I would effectively be neck sizing using the Redding Type S FL bushing die until I have had enough firings that have more fully fire formed the brass to the chamber so that I have enough expansion to enable a 0.002" bump sizing.

Appreciate any advice.
 

L.Sherm

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I think your on the right track. Cases that are all over the place are hard to get a consistent bump.
 

Mikecr

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I'd just jam seat & fire form the stuff to my chamber(like new brass).
Your chamber is your best die
 

jlvandersnick

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Hamilton, Montana
How can I determine which case was fired in my older rifle so that I don't have to full length resize all of them? I'm thinking of measuring the headspace on each fired case as well as the case body diameter just in front of the belt and then separate them into the two groups by significant measurement differences. Will that work?

Yes....maybe
I have two different rifles of the same caliber, and use the Hornady version of what your getting from Forster. I'm sure it varies, from chamber to chamber....but on my two rifles there is a .002 difference
 

BC Sportsman

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Feb 18, 2020
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Thanks very much. I'm waiting for the Forster datum tool to arrive in the mail next week and then I'll find out. The good thing is I have a pile of known old rifle fired brass and another pile of known new rifle fired brass. I'll see if there is a difference between the two lots and if there is, then I can go thru the mixed batch and separate.
 

sp6x6

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I have 2-338 NM. One is .001 tighter.I size and check both once in a while.Sometimes just running brass threw die twice does it.
 

tim_w

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Mar 25, 2008
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FL size them enough to fit your chamber and fireform them.

Its only 100 or so cases you can measure the datum to base and sort them that way. They should be fairly consistent between the 2 rifles. At least you should be able to pull yours out this way. Then size them as 2 or more group. Run a test sample of each thru a fl die and see how they compare to each other. Adjust for each group to get you the headspace you desire.

But no matter what I would keep them grouped until they all have been fired thru your chamber again.
 

C S Fever

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May 11, 2014
Messages
30
Get a good headspace gauge and measure them. And find what your chamber is and bump everything 0.002” down so that it chambers with slight to no pressure. Or full-size to SAAMI and start over! 🤷🏻‍♂️
 

Mike Matteson

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Jun 26, 2017
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Resize them all and start over again. My sons and I have rifle of same case, and use the same bullets, but mine rounds will go into their rifles, but I can't chamber their cases into mine. They were built by the same man at different times. I believe that when setting up the chamber there is a little different each time. It doesn't take much to change the chamber some.
The other is I believe that belted mag are head spaced off of the belt and not off of the shoulder. Correct me if I am wrong, please. I can see the bumping on the non-belted case to allow it to chamber, but question bumping on belted cases. I have use a 300 Win Mag Neck sizing die for my 308 Norma Mag for a great many years. The real different is the 300 win has a shorter neck because the case length is a little longer to the shoulder and to the neck is longer too. That die doesn't allow me to size the entire neck on the 308 N. Mag cases. (Never had a problem either). The 300 win mag was done to gain some added area for powder. They could fit it into a shorter action instead of using 300 H & H case that requires a long action bolt. Beside that Winchester wanted was to sell rifles. It's a great round, and does out due the 308 N. Mag.

SSS
MIke
 

BC Sportsman

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I should add that I want to bump 0.002" since I will be using the reloaded rounds (with Barnes 190 gr LRX) for both long range shooting practice and hunting. There seem to be 3 camps of advice here that accommodate my desire to bump size:

1) Full size all cases from both the new and old rifle to SAAMI specs without using any bump. Then bump after they have been fired in the new rifle...or
2) Cull cases using headspace measurements to separate those fired in my old rifle. Full size all the old rifle cases to SAAMI specs without any bump as per option 1 above. Full size cases that I can confirm were fired in my new rifle using a 0.002" bump...or
3) Cull cases for headspace measurements to identify the cases fired in my old rifle and keep these batches separate from each other. Full size all the cases from both rifles using a 0.002" bump from the new rifle's max headspace. As long as the cases from the old rifle chamber easily after resizing with a 0.002" bump, I won't have any problems with the bolt seizing up or worse happening.​

What I'm thinking of doing is first measuring all my brass to see if there are two distinct headspace measurement groups. I have some brass that I know came from my old rifle (I have since sold it) and my new rifle. If there are two distinct groups with no chance of doubt, then I will go with option 2.

If I can't find any measured differences that fall into two distinct groups, then I will resize all to SAAMI specs without doing any bump. My Forster datum dial tool should arrive next week.

Thank you everyone for your advice!
 

Philward

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Oct 17, 2015
Messages
170
I'm going with the full length size group, and when you are done developing your load they will all(maybe)have been fired through your rifle and at that point problem solved.
 

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