Full length die sizing - how much movement?

[Oldschool1]

Well i just got to wondering, if you have a factory Savage 12 F-class, what are likely the dimension of that chamber to wrt full length sizing and "over-working" the brass.

Being a factory barrel, I imagine it has to be a minimum size (and maybe more than that due to tolerances) to allow the largest case which meets specifications, so that it chambers.

So things coming to mind that keep me up at night (writing questions such as this ) are:

1. if the die works the brass overly small there is excess "slop" allowing the base of the die to "float" randomly causing alignment variation when the cartridge is chambered

2. The case will certainly now be resting on the neck/throat setting alignment w/o bullet pushed into the lands. (may not be good for alignment.

3. brass may not last as long due to working and thinning the walls, excessive length trimming as well.

4 A question, what is the neck wall thickness of Lapua brass - ending OD on no turn brass with bullet seated, this goes back to neck clearance and alignment.

My options on sizing dies currently are - which economy and benefit of non-bushing die:

A, Harrells can match a tight / loose die based on fired cases, but i still have a bushing die which i'd rather go to a honed neck dim on the FL die.

B. Forster std body with a honed neck for neck tension.

My issue is -hard to make decisions not knowing which dies produce what dims on brass compared to my actual chamber dimensions.

This requires thought!!!

thx,

Paul

 

[RockyMtnMan]

I think you're worrying too much. Unless you want to buy a reamer to your own specs and install a custom barrel, you have to work with what you got.

I'd be worried more about misalignment caused by a poorly cut factory chamber than I would about issues caused by a sizing die.

Set headspace tight on the FL die, 'kiss' the lands with the bullet, and try to get it shooting.

 

[Oldschool1]

Well maybe

Though i like to know what I'm doing and why.

1. I guess one approach is start, figure out what you don't know and improve.

2. Second approach gain preliminary information, develop a hypothesis about the way it should work wrt physics, have an expectation of the outcome, and improve from there.

I'm the latter method, so trying to learn about that, is important to me.

I do appreciate your comments though, that's good input.

I still am very curious about how much different dies move the brass? Especially the neck dimensions of FL dies.

Thx,

Paul

 

[dkhunt14]

The problem with a honed die is you are stuck with that tension it gives. If the bullets get fatter or skinnier, the tension changes. As you shoot the brass it gets harder and tension changes. The brass usually tends to get thinner the more times it is fired and that changes tension. Seeing you can tune with tension, I would rather have a bushing die so I can change it. Matt

 

[Barlow]

I use a Forster honed die in my 6 Dashers. The necks have been turned, and I anneal on third firing. Iirc my neck tension is .003. If I want less tension I use a K&M expander mandrel to get to .002 or even .001. Runout is the same, very low to 0. Not saying it's for everyone, but works for me. Also the guys at K&M are experts at their craft. Barlow

 

[Oldschool1]

Matt

How often due you switch bushings did that you can chase thinking walls. How far do you chase them to get constant neck tension as it thins

Thx

Paul

 

[RockyMtnMan]

Matt

How often due you switch bushings did that you can chase thinking walls. How far do you chase them to get constant neck tension as it thins

Thx

Paul

That depends completely on how thin the neck walls are getting. If the neck tension you are using works well for accuracy and the neck OD of a loaded round after 5 firings now measures .001" or .002" thinner, then you use a bushing that is .001" or .002" smaller to maintain the similar tension. If that doesn't seem to bring the accuracy back fully, use a bushing that is another .001" thinner. Simple.

You also have to understand that as the lands and grooves wear on a barrel, the characteristics of the accuracy may begin to change all together. So you will most likely have to chase the lands to maintain the same jump or jam. And sometimes accuracy can change so dramatically during the middle to end of a barrels life that you may have to change your powder charge weight or perhaps even change your load recipe all together.

But every barrel is different. There is no 'magic' formula that is one-size-fits-all.

 

[Oldschool1]

Thx Matt - that is helpfully. Lots to learn and I like that.

Paul