How much should head space increase with new brass?

[montana_native]

My terminology probably isn't correct, but when comparing new brass to fired brass in a recently rebarreled 300 Win using a Hornady gauge, I am seeing an average of a 0.018" increase.

This is with Hornady and Win brass. Really the only reason I checked this was because I was trying to diagnose a FTF issue.

Does this sound like the reamer was run too deep or are both brands of brass undersized, or is this normal? In my 6.5x47 (the only other new brass I have available) I measure a 0.006-0.007" increase.


Thanks.

 

[GrocMax]

Belted magnums headspace on the belt, not the shoulder.

 

[jepp2]

Does this sound like the reamer was run too deep or are both brands of brass undersized, or is this normal?

On the first firing, the brass headspaces off the belt. The 0.018" growth is normal for what I have seen. For subsequent sizing and firing, set your die so it headspaces off the shoulder. If you don't, it will last about 3 firings before you see signs of incipient case head separation.

 

[hoz53]

On the first firing, the brass headspaces off the belt. The 0.018" growth is normal for what I have seen. For subsequent sizing and firing, set your die so it headspaces off the shoulder. If you don't, it will last about 3 firings before you see signs of incipient case head separation.

Jepp has this one right. Technically belted magnums are supposed to headspace off the belt but you should headspace off the shoulder after the first firing or your brass won't last long. .002 shoulder bump is a good figure to shoot for.

 

[montana_native]

Thanks guys. I learned quickly how to correctly resize belted magnum brass many years ago after case head separation issues from just a few firings.

I'd never checked headspace "growth" before on new brass but I'm glad to learn that this doesn't seem to be a chambering issue.

Thanks again.

 

[Ledd Slinger]

I agree that the first firing growth is nothing to worry about since you have the belt securing the case.

How many FTF's have you had? The issue could be something else if they are a common occurance. If it was just one time, then it was probably a bad primer.

 

[KenOath]

On the first firing, the brass headspaces off the belt. The 0.018" growth is normal for what I have seen. For subsequent sizing and firing, set your die so it headspaces off the shoulder. If you don't, it will last about 3 firings before you see signs of incipient case head separation.

Jepp has this one right. Technically belted magnums are supposed to headspace off the belt but you should headspace off the shoulder after the first firing or your brass won't last long. .002 shoulder bump is a good figure to shoot for.

These guys are both on the money.

Cheers Rushty

 

[bsekf]

+3 on belted cases. Case stretch depends on many things, including case design and pressure. Never measured it, just trimmed it.

Bill

 

[Webster]

My terminology probably isn't correct, but when comparing new brass to fired brass in a recently rebarreled 300 Win using a Hornady gauge, I am seeing an average of a 0.018" increase.

This is with Hornady and Win brass. Really the only reason I checked this was because I was trying to diagnose a FTF issue.

Does this sound like the reamer was run too deep or are both brands of brass undersized, or is this normal? In my 6.5x47 (the only other new brass I have available) I measure a 0.006-0.007" increase.


Thanks.

My terminology probably isn't correct, but when comparing new brass to fired brass in a recently rebarreled 300 Win using a Hornady gauge, I am seeing an average of a 0.018" increase.

This is with Hornady and Win brass. Really the only reason I checked this was because I was trying to diagnose a FTF issue.

Does this sound like the reamer was run too deep or are both brands of brass undersized, or is this normal? In my 6.5x47 (the only other new brass I have available) I measure a 0.006-0.007" increase.


Thanks.

Wiki explanation of headspace. They explain that no matter which case dimensions are measured the headspace is to ensure the proper space between the bolt face and case head to get a proper firing pin strike. That explains the shoulder getting blown forward.

https://en.wikipedia.org/wiki/Headspace_(firearms)

 

[jepp2]

Wiki explanation of headspace

It is interesting on the rimless bottleneck cartridge, they got the words right but the drawing wrong.

 

[montana_native]

I agree that the first firing growth is nothing to worry about since you have the belt securing the case.

How many FTF's have you had? The issue could be something else if they are a common occurance. If it was just one time, then it was probably a bad primer.

The FTF rate on new brass is about 10%. On fired and sized brass, I've not experienced a FTF yet. Firing pin protrusion seems to be good and the firing pin spring is near new. Thanks.

 

[dedogs]

The FTF rate on new brass is about 10%

Sounds as if you may have a generous chamber. Are you full length sizing this new brass or just loading and shooting? dedogs

 

[Richard Jones]

It is interesting on the rimless bottleneck cartridge, they got the words right but the drawing wrong.

This is poorly done, but...............

 

[GrocMax]

I only deal with one belted mag, but there sure seems to be a very wide difference between brands of brass on what the belt headspace dimension is.

 

[LCazador]

The FTF rate on new brass is about 10%. On fired and sized brass, I've not experienced a FTF yet. Firing pin protrusion seems to be good and the firing pin spring is near new. Thanks.

Since a belted mag case headspaces on the belt, a FTF is probably not due to excessive headspace unless you have some weird cases. Sounds like you may have a bolt issue or firing pin issue.

 

[spclark]

Since a belted mag case headspaces on the belt, a FTF is probably not due to excessive headspace unless you have some weird cases.

Unless as he suspects the reamer might have been run in too deep? Wouldn't this cause the belt recess at the breech to be deeper than spec which would let cases move too far forward when chambered?

How do you measure this kind of thing when the dimension needing to be gauged is from the bolt face (bolt closed & locked to the front of the belt recess on a mounted barrel?

 

[Eric Leonard]

I think if I was doing a belted magnum I would want the reamer made so the case would headspace off the shoulder like their was no belt,even on the first firing,,
but with all the short mag and full length mag cases we have now I doubt ever building a rifle that takes a belted case,,

you should be able to get go/no go gauges to check the headspace of the belt,,if the no go gauge will let the bolt close the headspace would be to long??

 

[Webster]

This is poorly done, but............... View attachment 1003757

I think your drawing correction is good for head space. Depends on where contact is made to make it harder to close the bolt? The reference point most likely would be to the place on the shoulder that moved forward the most from firing? The shoulder location that would contact the chamber shoulder and make the bolt a little harder to close. Not sure if there is a definite shoulder location on all rifles where contact is made. My guess is that it isn't the location of the neck/shoulder junction that causes hard bolt closure, it could be. Never paid attention to it but I never remember seeing a shiny spot there.

Interesting discussion. Hope it doesn’t turn into a pissing match. Looks like 2-3 similar measurements for different purposes.

1. The gunsmith uses go/no go gauges to make sure the chamber he is cutting is within SAAMI specs. No bump gauge used here.

2. The term head space refers to getting the space between the bolt face and case head correct for a good firing pin strike. The go/no go gauge does this. Cutting the chamber to SAAMI Spec doesn’t explain why the OP had such a large increase in case growth using a bump gauge after firing new cases. Without re-reading the OP I believe he said after firing a new case, it grew over 0.010” using a bump gauge. The only thing I can think of to account for growth from the head to shoulder is that the case head to shoulder is intentionally made short to make sure that loaded factory ammo will chamber in any rifle. Even though the chamber is made properly the case is short and may cause a little too much clearance from bolt face to case head. The firing pin must push the case forward a little when shooting a new factory round. The factory knows what works. After its shot once in our rifle the case fits our chamber better and the distance from the bolt face to case head is improved and the case shoulder is a better fit to the chamber shoulder. Bump gauges should be used after 1-2 firings.

3. With a shoulder bump gauge you are measuring from the case head to some non-standard point on the shoulder on a fired case. It doesn’t matter where on the shoulder since you are looking for change only. Mid shoulder is probably where it’s indexed?

None of this above probably means much since most of us know how to reload quality ammo.

Comments welcome. Except from FGUFFEY.

 

[hoz53]

I think your drawing correction is good for head space. Depends on where contact is made to make it harder to close the bolt? The reference point most likely would be to the place on the shoulder that moved forward the most from firing? The shoulder location that would contact the chamber shoulder and make the bolt a little harder to close. Not sure if there is a definite shoulder location on all rifles where contact is made. My guess is that it isn't the location of the neck/shoulder junction that causes hard bolt closure, it could be. Never paid attention to it but I never remember seeing a shiny spot there.

Interesting discussion. Hope it doesn’t turn into a pissing match. Looks like 2-3 similar measurements for different purposes.

1. The gunsmith uses go/no go gauges to make sure the chamber he is cutting is within SAAMI specs. No bump gauge used here.

2. The term head space refers to getting the space between the bolt face and case head correct for a good firing pin strike. The go/no go gauge does this. Cutting the chamber to SAAMI Spec doesn’t explain why the OP had such a large increase in case growth using a bump gauge after firing new cases. Without re-reading the OP I believe he said after firing a new case, it grew over 0.010” using a bump gauge. The only thing I can think of to account for growth from the head to shoulder is that the case head to shoulder is intentionally made short to make sure that loaded factory ammo will chamber in any rifle. Even though the chamber is made properly the case is short and may cause a little too much clearance from bolt face to case head. The firing pin must push the case forward a little when shooting a new factory round. The factory knows what works. After its shot once in our rifle the case fits our chamber better and the distance from the bolt face to case head is improved and the case shoulder is a better fit to the chamber shoulder. Bump gauges should be used after 1-2 firings.

3. With a shoulder bump gauge you are measuring from the case head to some non-standard point on the shoulder on a fired case. It doesn’t matter where on the shoulder since you are looking for change only. Mid shoulder is probably where it’s indexed?

None of this above probably means much since most of us know how to reload quality ammo.

Comments welcome. Except from FGUFFEY.

You can get a headspace gauge which measures from case base/bolt face to front of belt. If the headspace checks okay you know the reamer wasn't run in to far but may have been a little longer from base to shoulder dimension than you would like. Still it's within Specs. Since manufacturers use the base to front of belt dimension for there "official" headspace dimension base to datum has varied quite a bit. They ream them so they will accept all factory loads which usually means a little long. Then the brass manufacturers tend to make base to datum a little short so their brass will fit all chambers. Thus we often have quite a bit of headspace. All because saami spec is headspace off belt instead of shoulder. Good news is you start sizing off shoulder after first firing most people seem to get good case life even though the case has stretched so much on first firing.

 

[ireload2]

I have seen new .303 British brass blow the shoulder forward about .060 on the first shot when fired in a Lee-Enfield rifle.

The Lee-Enfield rifle chambers just don't resemble the ammo as close as we are used to.