Excessive?

[Jody Simcox]

What is the difference in thousands between the OD of a loaded round and a fired round?

Loaded- .3025”
Fired- .3095”
FL sized- .2985”
Expanded- .3005”

 

[dcali]

Loaded virgin Nosler brass in 270win with a 130 AB 18 mos ago. Measured the OD of the necks of loaded rounds, then ordered a FL sizer from Forster with the neck honed to .004” under (as they suggested). I then use an expander to get back 2 of those 4 thousandths before seating. Recently, I noticed that the difference between the OD of a fired case neck and a sized case neck is .011”.... a buddy says that’s crazy and I shouldn’t be moving brass that much... is he right? What could/should I do differently? Thanks

Fired brass size is determined by the chamber neck diameter and nothing else. Neck tension is the difference between the ID of the sized brass and the bullet diameter. What you’ve learned is why we shoot tighter than SAAMI chambers.

Most of us aim for about .004 clearance between then loaded neck diameter and the chamber neck diameter. That means your brass will grow only about .003 on firing. You can then size it down .005 and wind up with .002 of neck tension.

Now if your chamber is allowing it to grow .011, that means you have about 12 thousandths of clearance (there is about .001 of spring back). You then have to size it down .013 to get your .002 of tension. That is just unnecessary brass working, which can contribute to runout and poor brass life.

 

[_Raining]

If you turn the necks itll be even worse

How so?

His current configuration is:
Loaded- .3025”
Fired- .3095”
FL sized- .2985”
Expanded- .3005”
.3095” - .2985” = .011"

If he needs to turn off 1 thou to make the necks uniform then he can do the following:
Fired- .3095”
FL sized with bushing to - .2995”
Loaded- .3015”
.3095” - .2995” = .01"
It will expand 1 more thou on firing but 2 thou less during sizing.

The only way it wouldn't be better is if he needed to turn off 2 thou or more to achieve uniform necks.

Or am I missing something?

 

[Had2muchofForums]

If he makes the neck diameter smaller by neck turning, his brass will expand to the chamber wall that much more on each firing.

 

[_Raining]

If he makes the neck diameter smaller by neck turning, his brass will expand to the chamber wall that much more on each firing.

Yes, if he turns off 1 thou of his neck then it will expand 1 thou more BUT it will be sized 2 thou less during the sizing process bc he can use a bushing instead of sizing 2 thou extra then pushing it out with an expanding mandrel. The mandrel is only used bc the necks are not uniform so if you uniform them by turning then that step is not necessary.

It is only 1 thou difference but I don't understand the people saying it will make it worse.

 

[Dusty Stevens]

Yes, if he turns off 1 thou of his neck then it will expand 1 thou more BUT it will be sized 2 thou less during the sizing process bc he can use a bushing instead of sizing 2 thou extra then pushing it out with an expanding mandrel. The mandrel is only used bc the necks are not uniform so if you uniform them by turning then that step is not necessary.

It is only 1 thou difference but I don't understand the people saying it will make it worse.

If the brass expands .001 more upon firing thats worse than not. Id rather cold work it more than blast it out more

 

[_Raining]

If the brass expands .001 more upon firing thats worse than not. Id rather cold work it more than blast it out more

Interesting, do you know of any articles that go over the differences between working the brass under fire and working it with a reloading die?

 

[Dusty Stevens]

Interesting, do you know of any articles that go over the differences between working the brass under fire and working it with a reloading die?

No i dont. I just go by what i see.

 

[_Raining]

Loaded to fired is .007 not .011

Yes I am aware.
I looked over my math once more and figured out where my logic was flawed. I should have done the combination of fired expansion and reloading sizing.

So a round trip for his current configuration is:
.007 + .011 = .018

For 1 thou turned off it is:
.008 + .010 = .018

For .5 thou turned off it is:
.0075 + .0095 = .017

So the only way to save working the brass is by using a bushing and turning off 0 up to but not including 1 thou, which would produce:
.016 up to but not including .018

As for rather having the brass worked less under fire than sizing, I have no opinion on this matter as I have no experience with it nor do I have any sources of tests done to determine the effects.

 

[Uncle Ed]

In a off the shelf factory rifle you have no control over how how much the neck expands when fired.

And using a bushing die to reduce the neck diameter this much can induce neck runout.

And if Jack O'Connor was here he would tell the OP his .270 Winchester is the worlds best non-belted magnum.