Resizing question

[m1ajunkie]

I am using an rcbs full length sizer die to resize my federal brass for my .308 load.

I am trying to mimic the case size of the fgmm load that this brass was orginally fired as. According to my hornady headspace gauge on my caliper I get the headspace measurement at 1.6205" almost everytime.

However when I resize my brass I am getting cases in a range of 1.620-1.624" in headspace.

What is causing this spread in my brass? Anything I need to change, or is this normal?

 

[FLIGHT762]

Re: Resizing question

Different lubes or inconsistent lubing will cause this and/or along with pulling the expander ball back through the necks of unlubed necks causing galling. The necks may need some lubing inside.

Work hardening of the brass can also cause inconsistent spring back. Annealing can help, depending how many times the brass has been fired.

You need to experiment a bit to see what will provide consistent results. I found Imperial wax gave me consistent results.

 

[m1ajunkie]

Re: Resizing question

Thanks for the help. I am using imperial for lube, but I think I need on living the case mouth. The outside the case I am covering well, the the case mouth just gets a smidge around the rim with my finger tip.

 

[milo 2.0]

Re: Resizing question

Will the "1.624" length chamber in your gun? If they do you're probably ok.

 

[m1ajunkie]

Re: Resizing question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: milo-2</div><div class="ubbcode-body">Will the "1.624" length chamber in your gun? If they do you're probably ok. </div></div>

They will chamber fine. I just figured the variation wouldn't have a great effect on accuracy.

 

[Bayou]

Re: Resizing question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: m1ajunkie</div><div class="ubbcode-body">....I am trying to mimic the case size of the fgmm load that this brass was orginally fired as....</div></div>

I don't understand the motivation for this objective? Federal sells ammo with cases that have some "average SAAMI" dimensions that will work well in thousands of different chambers that have slight chamber dimension variations. Why target something that's probably not optimum for your one single chamber? I target a 2X fired case for bumping the shoulder. All you need (or want) for chambering is a thou or two of clearance. So if set your sizing die to give the same headspace reading as brass fired from your rifle and the case chambers easily you're good.

On a separate issue, identifying the cause of variations in the case dimensions and eliminating them is definitely a worthwhile endevour.

 

[Squid284]

Re: Resizing question

Is the shellholder contacting the bottom of the sizing die every time? (is the handle camming over a little at the top of the stroke?) Contact should keep the shoulder at the same spot on every round or at least +/- .001". .004" of variation sounds excessive.

You might be able to adjust your die, or use shims or redding comp shellholders to reduce the variation from case to case.

I agree that matching the dimensions of box ammo is probably not going to yield better accuracy. I like to set the shoulder back .001" (bolt gun) or .003" (semi-auto) compared to a fired casing.

 

[Unknown]

Re: Resizing question

I'm guessing that the length disparity is most likely caused by not having enough lube on the inside of the neck. When this happens, as you pull the case over the expander ball, there is enough friction to pull the neck outward a tiny bit causing the difference. The other cause was mentioned above, and if you are using cases that have a variety of firings (some cases fired 2x, some 4x since annealing) that variance will cause some spring back disparity.