Prepping fireformed brass

[Shooterdevil]

Now that I have some fire formed casings for my 6.5CM, I have a question when it comes to shoulder bump. From what I've seen from researching, it appears it is common to bump the shoulder back instead of full length resize. Some people use a FL sizing die to accomplish this by just backing out the die slightly to achieve the desired bump. Using a headspace comparator I took a baseline on the fire formed brass and then I FL sized a brand new case to see where the headspace was before attempting to back it out. The new FL sized casing measured -.0025" on the calipers which means it is already shorter than the fire formed by that amount. I was originally going to try bumping .003 just to start but it seems with a FL size, I'm practically there. Seeing as I do not wish to FL size my fireformed brass, does this mean I'm better off getting a die dedicated to shoulder bump?

 

[Bill Norris]

Now that I have some fire formed casings for my 6.5CM, I have a question when it comes to shoulder bump. From what I've seen from researching, it appears it is common to bump the shoulder back instead of full length resize. Some people use a FL sizing die to accomplish this by just backing out the die slightly to achieve the desired bump. Using a headspace comparator I took a baseline on the fire formed brass and then I FL sized a brand new case to see where the headspace was before attempting to back it out. The new FL sized casing measured -.00025" on the calipers which means it is already shorter than the fire formed by that amount. I was originally going to try bumping .0003 just to start but it seems with a FL size, I'm practically there. Seeing as I do not wish to FL size my fireformed brass, does this mean I'm better off getting a die dedicated to shoulder bump?

If the appropriate die for your chamber is adjusted properly the F/L die will size the brass correctly.

 

[Kracken McGraw]

Now that I have some fire formed casings for my 6.5CM, I have a question when it comes to shoulder bump. From what I've seen from researching, it appears it is common to bump the shoulder back instead of full length resize. Some people use a FL sizing die to accomplish this by just backing out the die slightly to achieve the desired bump. Using a headspace comparator I took a baseline on the fire formed brass and then I FL sized a brand new case to see where the headspace was before attempting to back it out. The new FL sized casing measured -.00025" on the calipers which means it is already shorter than the fire formed by that amount. I was originally going to try bumping .0003 just to start but it seems with a FL size, I'm practically there. Seeing as I do not wish to FL size my fireformed brass, does this mean I'm better off getting a die dedicated to shoulder bump?

I think you have got a extra zero in your figures.

 

[Shooterdevil]

I think you have got a extra zero in your figures.

You are absolutely right. Thanks for the catch

 

[Shooterdevil]

If the appropriate die for your chamber is adjusted properly the F/L die will size the brass correctly.

Would this defeat the purpose of trying to keep the brass formed to the chamber?

 

[Kracken McGraw]

To your original question you might as well set your FL die where you want it, or otherwise you will have to neck size in another step someway.

 

[Bill Norris]

Would this defeat the purpose of trying to keep the brass formed to the chamber?

Not at all. If you only bump the shoulders with a bump die at some point down the road the brass will become too tight at the 200 line. At that point you will need to re-size that portion of the case in order to realize easy chambering and avoid clickers.

 

[Shooterdevil]

To your original question you might as well set your FL die where you want it, or otherwise you will have to neck size in another step someway.

At its current setting it leaves the shoulder at .0025" shorter than once fired brass. Which is about where I wanted to bump the shoulder to anyway. Thing is at that depth it would FL size the brass too.

 

[Bottom Fodder]

I bump my shoulder using my neck sizing bushing die

 

[Kracken McGraw]

At its current setting it leaves the shoulder at .0025" shorter than once fired brass. Which is about where I wanted to bump the shoulder to anyway. Thing is at that depth it would FL size the brass too.

That’s what your wanting to do to make the round chamber easy.
Go to Alex Wheeler’s website and watch his video on the subject.

 

[Shooterdevil]

That’s what your wanting to do to make the round chamber easy.
Go to Alex Wheeler’s website and watch his video on the subject.

What is the website?

 

[Kracken McGraw]

What is the website?

https://www.wheeleraccuracy.com/

 

[Ned Ludd]

Sizing a fire-formed case with an FL sizing die does not "undo" the fire-forming process. It merely sizes the case down by a small amount so that it will chamber easily and consistently. Adjusting the shoulder bump so that the re-sized case is shorter at the shoulder by ~.0015" to .002" will also set the die to properly size the case body. In other words, use the bushing you want for the appropriate neck tension/interference fit, and set the FL sizing die to consistently bump the shoulder by about .0015" to .002". That's all you need to do.

 

[MUP]

Also, are you certain you have fully fireformed the cases with just one firing? Sometimes multiple firings are required to fully form the cases to the chamber, and with just one firing you may, or may not have reached the full chamber form just yet. I would measure the chamber to be certain before attempting to bump the shoulder back any.

 

[K22]

I F/L size all my cases every time because reliability is just as important to me as accuracy.

I use a bump gauge and caliper to set the F/L die to zero to .001' bump (bolt rifles) on new cases until they are fully fired formed which may require a few firings. It is also important in the F/L sizing process that you do not extrude (lengthen) the case which can occur if the shoulder of the case does not make contact with the die.

I find that because the F/L die also sizes the radial dimension of the case, bumping the shoulder is often not required for several firings. You only need to bump if at all, the amount necessary to provide optimum chambering of the case. No more, no less. Don't get hung up on a specific number, let the rifle chamber tell you the amount that is optimum for your rifle and brand of cases.

There is nothing magically about properly sizing cases if you have a bump gauge and a caliper. Measured the fired cases (primer removed) then adjust the F/L die to size the case the desired amount. It's really quite simple. The process in greatly enhanced by starting with virgin cases, dedicating a group of cases to a specific rifle and rotating their firing / sizing's.

I also occasionally spot check sized cases in the rifle chamber (firing pin assembly removed) to verify optimum sizing.

 

[Mike TackleBerry]

Now that I have some fire formed casings for my 6.5CM, I have a question when it comes to shoulder bump. From what I've seen from researching, it appears it is common to bump the shoulder back instead of full length resize. Some people use a FL sizing die to accomplish this by just backing out the die slightly to achieve the desired bump. Using a headspace comparator I took a baseline on the fire formed brass and then I FL sized a brand new case to see where the headspace was before attempting to back it out. The new FL sized casing measured -.0025" on the calipers which means it is already shorter than the fire formed by that amount. I was originally going to try bumping .003 just to start but it seems with a FL size, I'm practically there. Seeing as I do not wish to FL size my fireformed brass, does this mean I'm better off getting a die dedicated to shoulder bump?

If this is once-fired brass chances are it's not fully fireformed to your chamber, It takes me around 2-3 firings for the brass to be fully formed to the chamber! When I bump the brass I only bump the shoulders back .001, Then I take the brass and verify it fits into my chamber! Once all the brass is fully fireformed and all the brass has the same headspace then I'll bump all the brass back by .002 and run it!

 

[Shooterdevil]

Lots of good info in the replies so far. I appreciate it!

 

[jackieschmidt]

Sooner or later, you are going to have to start full length sizing your cases, probably after the third firing.

So the best thing to do is full length size from the very start and tune accordingly.

 

[Coyotefurharvester]

You can set your die to 1. FL size -shoulder lengthens(wrong) 2. FL size with no shoulder length change, typical for fired brass that chambers easily 3. FL size moving the shoulder toward the base, because the brass doesn't chamber correctly because the shoulder is contacting the chamber surface before the bolt closes. How much you need to bump brass that NEEDS the shoulder moved will be a feel/bolt operation judgement. Or you can use a spent primer to measure the bolt face to case headspace(clearance). My hunting rifles 0.001-0.002, AR's 0.003-0.004 works well when hunting in below freezing temps and avoiding forward assist to battery.

 

[Bill Norris]

^^^^^^^^ Exactly Jackie.