Yet another head space question

[C Valentine]

After I had a new barrel installed on my Savage 12 .223, I was advised to FL size my brass before firing in the new barrel. Any brass that measured over minimum got the shoulders bumped to SAMMI minimum (zero on my Precision Mic). After firing, all of the cases measured -.002 to -.003 BELOW SAMMI min. Same with new cases. Actually the new Lapua cases almost all measured about -.002 to -.003 below out of the box, and they did not grow with firing. Is this okay or should my headspace be adjusted on the rifle? The bolt is a bit stiffer to close than it was with the factory barrel. The barrel maker says their chambers are reamed to SAMMI minimum. I am just learning about all this stuff and my eyes are starting to glaze over! Thanks for your patience and advise!

 

[243winxb]

A cruch fit when closing the bolt will tell you when the brass is the same size as the chamber. Then measure with your tool and bump the shoulder back .002" The head to datum may get shorter on firing with starting loads. The firing pin strike from my Savage sets the shoulder back .006"

 

[CatShooter]

A cruch fit when closing the bolt will tell you when the brass is the same size as the chamber. Then measure with your tool and bump the shoulder back .002" The head to datum may get shorter on firing with starting loads. The firing pin strike from my Savage sets the shoulder back .006"

It is not the firing pin, it is the force of the primer (which is a LOT).

 

[gunsandgunsmithing]

If I understand your question correctly, I'd guess that you're using new brass. The datum line moves once it's formed to your chamber, slightly. Think about it.

 

[243winxb]

A cruch fit when closing the bolt will tell you when the brass is the same size as the chamber. Then measure with your tool and bump the shoulder back .002" The head to datum may get shorter on firing with starting loads. The firing pin strike from my Savage sets the shoulder back .006"

It is not the firing pin, it is the force of the primer (which is a LOT).

No, its the firing pin strike that sets the shoulder back.

 

[CatShooter]

A cruch fit when closing the bolt will tell you when the brass is the same size as the chamber. Then measure with your tool and bump the shoulder back .002" The head to datum may get shorter on firing with starting loads. The firing pin strike from my Savage sets the shoulder back .006"

It is not the firing pin, it is the force of the primer (which is a LOT).

No, its the firing pin strike that sets the shoulder back.

Try it with a primer that is dead... no change in headspace, no nothing - but the force of a primer will put a large dent in a cooking pot. I have the tee shirt (and the dented stainless steel pot)

 

[mikecr]

Neither firing pin strike, nor primer ignition affect my headspace. I've tested in 6br, 6xc, 26wssm, and 223, after reading implication of it elsewhere.
I'm not convinced of any centering either..

 

[Scott Harris]

Have your chamber checked with a GO gauge...if it fits all is well....if not it needs to be fixed

 

[gotcha]

+1 for Scott. Also, Savage firing pin on .223 should have .040" protrusion. That's where my VLP is set And I get nowhere near .006" shoulder set back. If a Smith checks your head space with a Gauge have him check the firing pin protrusion also. .... The .223 is a pretty thin case and will fire form readily. However, Lapua brass will sometimes require two fire formings (moderate loads) to completely form. I've learned this the hard way ...... It sounds like your H/S is set a bit too tight. Do you have scuff marks from bolt face on rear of chamber?...... Or, will H/S shorten by merely chambering a round? Try it.

 

[CharlieNC]

While your chamber may be fine, but the barrel may be screwed in too much. The barrel nut can be loosened to re-set the headspace if necessary.

 

[BCoates]

While your chamber may be fine, but the barrel may be screwed in too much. The barrel nut can be loosened to re-set the headspace if necessary.

^This. It sounds like the headspace was set too tight when the barrel was screwed into the action. You need to get a go gauge and reset the headspace.

 

[C Valentine]

Done. Since I needed some other work I hauled off on a road trip to my smith today and he relaxed the headspace a bit for me even though the N & NG gauges were okay as it was, the G gauge was just a bit stiff. Much more comfortable for me operating the bolt from prone now. Gettting some new brass next week so will see what happens with that. Thanks everyone.

 

[fguffey]

The datum line moves once it's formed to your chamber, slightly. Think about it.

My cases do not have head space, my chamber does. I measure the length of the case from the shoulder/datum to the head of the case. I use the case length to off set the length of the chamber.

My datums do not move.

F. Guffey

 

[fguffey]

The head to datum may get shorter on firing with starting loads.

For years I have accused reloaders of making this stuff, does anyone measure before and again after firing.

Boring story: A neighbor/reloader/builder/shooter called from a range, he wanted to know what was wrong with Remington ammo, I suggested he call Remington AND! the phone number was on the box. Seems a shooter and proud owner of a new Ruger rifle with two new boxes of Remington 30/06 ammo had 5 fail to fire rounds out of the first 20.

Later he shows up with the 5 fail to fire and the 15 fired cases. No box and no information on the owner of the Ruger. I measured the fired cases with everything I have, chamber gages, Wilson case gages, take off barrels, barrel stubs, most unusual, the fired cases would chamber in my chamber gages with slight thumb pressure. The 5 that failed to fire had been hit with the firing pin of every 30/06 rifle at the range meaning the primers had been hit at least 5 times each.

We tore the cases down and measured the components by weight and dimensions, magnificent ammo. We removed the primers, nothing loose, cracked or broken, we installed the primers back into the came cases. THEN we chambered the cases with primers in one of my M1917s, all 5 primers fired. I have killer firing pins, those that make this stuff believe the case, bullet, powder and primer takes off in a race to the shoulder of the chamber to avoid the firing pin strike.

I say time is a factor, I just can not find anyone that can think in milliseconds.

F. Guffey

 

[CatShooter]

The datum line moves once it's formed to your chamber, slightly. Think about it.

My cases do not have head space, my chamber does.

My datums do not move.

My wife's not short, I'm tall!!!

When the case shoulder is against the chamber shoulder, and there is space at the hed... you have headspace.(though others call it other names, including some that are not so polite).

When you fire the case for the first time, you loose the headspace at the expense of stretch.

It is easy.

 

[fguffey]

though others call it other names

They refer to the measurement as clearance, or the difference in length between the chamber and case when the chamber is measured from the shoulder to the bolt face and the case from the shoulder to the head of the case.

F. Guffey

 

[mikecr]

I'm sure most reloaders consider headspace as meaning space between case head and boltface while the case is fully forward in chamber.
This dimension changing as case expansion grips the chamber AND stretches back to the boltface, lengthening the body and reducing the next measure of headspace.
Seems like a sound way to view it.

 

[fguffey]

I'm sure most reloaders consider headspace as meaning space between case head and boltface while the case is fully forward in chamber.

And that makes for a very boring conversation, you are talking about clearance between the case and chamber/bolt face. then it gets very complicated when I find a reloader that can not keep up with case stretch.

I have head space gages, I make head space gages, head space gages should be used to measured the length of the chamber from the shoulder to the bolt face. I understand what you and other reloaders consider head space. On second thought, other reloaders should be allowed to speak for themselves.

F. Guffey

And my cases do not have head space.

 

[CatShooter]

F. Guffey

And my cases do not have head space.

Then you got cheated - send them back and get a refund - cases have headspace

The 1.634 -007 line is the headspace.

 

[fguffey]

Catshooter, I ask the question: "Do you guys just make this stuff up?" The drawing you posted is from SAAMI, the SAAMI case drawing is absent of a head space symbol. Had you included the chamber drawing you would have an ideal what a head space symbol looks like.

A member of another forum called SAAMI in an effort to get someone at SAAMI to agree with him, someone at SAAMI screwed up? SAAMI has been around long before the Internet. SAAMI also has a glossary of terms, in the glossary of terms SAAMI says reloaders are confused about clearance between the bolt face and case head.

F. Guffey