What size is my chamber? Measuring shoulders.

[TheCoyote]

.300WM
New Nosler brass measured with Hornady E420 headspace bushing 2.261" +/- 0.001" (nice job Nosler).

After firing one time 25 pieces of brass measure:
2.269" up to 2.275" so there is a variance of 0.006" The majority of them 2.271" to 2.272"
I understand that isn't a huge amount but I honestly thought that they would all be fire formed, smashed into that chamber and only vary maybe 0.0005"

I bought the Redding Type S full length bushing die but now I'm wondering what headspace should I resize these cases to?

Goal was 0.002' under the chamber dimensions. But is that under the biggest? The Average? I would assume under the biggest right? Why are they not the same length?

 

[sndmn11]

Take the 2.275 and size it without moving the shoulder, then see if it will chamber. If it will, load it up and shoot, remeasure the shoulder.

 

[BBob]

but I honestly thought that they would all be fire formed, smashed into that chamber and only vary maybe 0.0005"

It can take 3-4 firings to fully fireform.

 

[wapitibob]

It can take 3-4 firings to fully fireform.

this is the answer

It's a belted case and zero chance it will fireform in 1 shot. My belted stw brass grows .020" and takes 3 firings.

 

[Wrench]

You can smoke a case with a candle and see for yourself.

 

[Koda_]

I dont have any belted calibers and non have fully fireformed in one firing either. I also dont think fully fireformed matters. Bump your shoulder back .002" from your longest dimension and the rest will get there soon. You wont notice any practical difference in accuracy or velocity. Annealing helps bring them into consistency.

 

[elephantrider]

.300WM

2.269" up to 2.275" so there is a variance of 0.006" The majority of them 2.271" to 2.272"

I bought the Redding Type S full length bushing die but now I'm wondering what headspace should I resize these cases to?

Goal was 0.002' under the chamber dimensions. But is that under the biggest? The Average? I would assume under the biggest right? Why are they not the same length?

Your goal of 0.002" bump is about right. As others stated, not all of your brass is fully fire formed yet. Since it is a belted magnum, your brass may be 'headspacing' on the front edge of the belt until it expands to fit the chamber at the shoulder.

To set your FL dies bump, you need to check your fired brass in YOUR rifle/chamber. You will need to remove the firing pin/spring, and the ejector, and make sure the bolt lug and abutments are clean. You will need to see how each piece of brass chambers after you have done these, and THEN you can determine the amount of setback you need, and set your die accordingly. Erik Cortina will show it better than I can explain it.

As for die selection, I would prefer a Forster FL die with the neck honed out to the minimal amount of neck size, over a bushing die, but that's just me. I also remove the neck sizing button and set the neck ID in separate step using a neck mandrel. Since you are using belted magnum, there are also special collet dies that size the body just above the belt. You may need that if you are getting 'clickers' as your brass goes through more firings.

 

[wapitibob]

I don't run my brass thru a sizing die until it's been fired 3 times. Smoke the shoulder as wrench noted and bump when it's needed.

 

[TaperPin]

If a case is fully fireformed or not, if it chambers easily there is no benefit to pushing the shoulder back. Easy bolt closing is the goal, not the arbitrary .002”. I understand it’s an important aspect to selling Hornady’s gizmo, but pushing .002” from something that is already less than the full chamber defeats the intent of a minimal known pushback.

Luckily, the .002” isn’t critical since at least 95% of gizmo users are way off. If you don’t believe it, or are the curious type that enjoys exact measurements, cut shim disks out of feeler gauges and chamber a sized case with progressively thicker shims between bolt and case head until the bolt shows resistance. Same accurate measurement can be done with a group of cases that have grown to actually fill the chamber and are creating slight drag on the bolt - using feeler gauges to accurately judge die adjustments, get as close as possible to just a hint of bolt closure resistance, then adjust die for setback if desired.

Going back to the trendy idea of shoulder pushback, it’s intended to create the least amount of disruption to the rifle when chambering multiple rounds. I like to challenge the nephews to test the idea on their rifle to see if it makes any difference whatsoever. In all the years since this .002” has become popular I have yet to see anyone who has tested it with a noticeable difference. My 1/2 MOA rifles have all only been neck sized - would shoulder pushback and no bolt resistance make them any better as a hunting rifle? No.

I set dies to fully contact the shell holder then simply loosen the die an entire turn and lock it down - essentially neck sizes and there is some resistance on the bolt handle once cases fully fit the chamber. Simple. Accurate. Always works.

 

[TheCoyote]

Yeah good stuff thank you everyone for the responses. I'll just resize the necks then and shoot them all again.
Some people are adamant about full length resizing every time, some people are adamant about neck sizing only. Me, I dont't really know anymore...

 

[MallardSX2]

Why can't you just FF and only neck size?







Just kidding. lol

 

[TheCoyote]

Ah, the joke is on you @MallardSX2, I have no idea what FF means!

Fhone a Friend?
Find a Fiddle?

 

[wind gypsy]

FF = fire form.

I've tried just neck sizing with a collet die once with 6.5 creed after initial firing of brass and wound up with 90% of the rounds tight on bolt close.. I can see how it would work on belted mags that have a lot of stretching to do but I dont know how all the folks do it on standard cartridges that dont have a sloppy brass/chamber fit to start.

 

[MallardSX2]

Ah, the joke is on you @MallardSX2, I have no idea what FF means!

Fhone a Friend?
Find a Fiddle?

I thought it stood for what my grandad always said when you asked him a question that he didnt know the answer to......"I don't give a Fiddlers F" lol

 

[SDHNTR]

It can take 3-4 firings to fully fireform.

This. You are shooting a belted magnum. It heads spaces off the belt, not the shoulder. It will take multiple firings to fully stretch to fit the chamber..

 

[Koda_]

Yeah good stuff thank you everyone for the responses. I'll just resize the necks then and shoot them all again.
Some people are adamant about full length resizing every time, some people are adamant about neck sizing only. Me, I dont't really know anymore...

Full length sizing is more consistent, go with that. Learn how to bump your shoulder back .002" and you will work your brass the least increasing life.

 

[SDHNTR]

Full length sizing is more consistent, go with that. Learn how to bump your shoulder back .002" and you will work your brass the least increasing life.

There’s a huge difference between FL sizing belted mags and standard cartridges. There’s no need to FL size a belted mag in the first 2-3 firings. A belted mag has a country mile in front of the shoulders since it headspace’s off the belt!

 

[Koda_]

There’s a huge difference between FL sizing belted mags and standard cartridges. There’s no need to FL size a belted mag in the first 2-3 firings. A belted mag has a country mile in front of the shoulders since it headspace’s off the belt!

I read his question as asking what fireformed length to set his shoulder bump from.

 

[Truck24hr]

FF = fire form.

I've tried just neck sizing with a collet die once with 6.5 creed after initial firing of brass and wound up with 90% of the rounds tight on bolt close.. I can see how it would work on belted mags that have a lot of stretching to do but I dont know how all the folks do it on standard cartridges that dont have a sloppy brass/chamber fit to start.

Not to derail this dudes thread, but what brass were you using? I usually get 3 firings out of Lapua brass in a 6.5x47 before I have to bump the shoulders.

Usually 2 firings in my 5.56 bolt gun with Nosler brass

 

[wind gypsy]

Not to derail this dudes thread, but what brass were you using? I usually get 3 firings out of Lapua brass in a 6.5x47 before I have to bump the shoulders.

Usually 2 firings in my 5.56 bolt gun with Nosler brass

Berger factory ammo (lapua brass) fired once.