Thread: Shoulder bump question

So I’m wanting to FL size to bump my shoulders back .002” or there abouts from the point where my brass won’t chamber smoothly anymore (Erik Cortina method). But I’ve never found I have an issue rechambering fired brass. I put it to the test today, firing 4 pieces of brass 4 times each. Annealing and neck sizing only between firings. Interestingly the shoulders didn’t move forward at all and after 4 firings the brass chambered as smoothly as virgin brass. Now I’m thinking should I just neck size…

If you watch Eric Cortina I assume you have seen his video on only FL sizing?

Originally Posted by stagstalker

If you watch Eric Cortina I assume you have seen his video on only FL sizing?

Correct which is why I’d rather FL size but can’t find the point at which to size from. If you get what I mean. He shows his cases being hard to chamber, then sizing back .002”.

Originally Posted by Tuckerbox

Correct which is why I’d rather FL size but can’t find the point at which to size from. If you get what I mean. He shows his cases being hard to chamber, then sizing back .002”.

I would just bump .002” back from whatever they measure after being fired.

so.....you have tight dies and loose chamber....you could try winding die out more,1/2 turn or so and see what happens,partial length sizing...but then again...you have no problem to fix to begin with.
by partial length resize you will be only working some of neck,not all,and shouldnt alter shoulder or body much at all....it MIGHT be working brass less....similar to neck sizing....

Yeah keep neck sizing until they no longer chamber, then full or partial size, it'll work you brass less and help them last longer. I've neck sized the same brass half a dozen times and they still chamber mint.

Originally Posted by Three O'Three

Yeah keep neck sizing until they no longer chamber, then full or partial size, it'll work you brass less and help them last longer. I've neck sized the same brass half a dozen times and they still chamber mint.

Yes and no. It really depends on what type of die you are using to neck size. And also if you are annealing every firing (and exactly how well/consistently you are doing this).

The part I am mostly concerned about is the neck. In my world, neck tension is the be all and end all of accuracy. If you are sizing your neck by under-sizing it and then drawing it back through a button (basic, traditional style neck dies), you are actually working the neck brass quite a bit...

Using bushing dies or collet dies minimizes the amount of squeezing and stretching that happens.

My approach is to anneal each firing (using an AMP annealer), then bump the shoulder 0.002 back from a measured fired case, then size the neck using a collet die.

Think about it.......if you ever have to FLS you will have different performance to brass that is not sized. This only matters if you are loading for precision.

To determine case fit in the chamber you will have to unload your bolt and check the back lash against the locking lugs......you will be able to feel or measure that easily, but it is not possible with a spring load from the firing pin or maybe a strong ejector spring.

If you never have to FLS then you are OK to continue as each case will be sized exactly as the rest. This what you need to achieve by whatever means.......!

If you want to FLS simply measure the shoulders of a fired case with a head space comparator, and resize your cases to measure one to two thou less than that. This will only improve consistency on a 1/2 MOA rifle and it is doubtful if the rifle will not do this the improvement will be noticeable........!

Its interesting reading some of these comments again.

What I think a lot of people miss in all of this is that sizing is relative both to the chamber dimensions of your rifle and to the size of the brass.

The idea for me is to keep the brass for each rifle separate. Once it has been fire-formed in THAT chamber, you can carefully measure it to get an idea of baseline dimensions, and then start working from there.

To put this into context, factory sized brass is quite often significantly undersized so that it fits into a variety of chambers. And of course there are massive differences between different manufacturers when it comes to things like case thickness etc. Just on the shoulder datum measurement for virgin unfired brass, I have found as much as 8 thou difference between manufacturers.

Things also change over the lifespan of a rifle, so it is good to re-check the numbers every now and then, just as a sanity check.

And lastly, not all FLS is equal. Most of the top benchrest shooters in world full length size only, but of course that is with custom dies cut with the same reamer as their chamber... so not exactly your garden variety die.

@ebf I think you will find the custom die is not made from the chamber reamer. I make my own dies from what is called a resize reamer....some 0.004" smaller on critical dimensions. There is no way a chamber reamer can make a FLS die to reduce brass dimensions

Originally Posted by Longranger

@ebf I think you will find the custom die is not made from the chamber reamer. I make my own dies from what is called a resize reamer....some 0.004" smaller on critical dimensions. There is no way a chamber reamer can make a FLS die to reduce brass dimensions

Yup, should have said "similar"

@Longranger, is the normal roughing reamer you use smaller in dimensions than the resize reamer ? Can you use the rougher for both and then just run the resize or finishing reamer in ?

Hi @ebf .....roughing reamers are smaller than both just to remove the bulk of material to save the finishing reamer life cycle. I never use a roughing reamer preferring to cut the bulk of material with a single point tool to ensure concentricity to the bore then the finishing reamer follows those walls precisely........same procedure with the die making