The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: General

Reply
 
Thread Tools Search this Thread
Old December 30, 2018, 04:00 PM   #26
hammie
Senior Member
 
Join Date: March 18, 2009
Location: Temple, TX
Posts: 681
The attached illustration in post number 3, seems to indicate that the cartridge head is located somewhere near the top surface of the cartridge web. However, the context of the way most of you are using "head" seems to mean that the head is the cartridge base. What is the head? Is it the base? Is post #3 wrong?


I'm not disputing anything. It would just be nice to have some clarification. Sorry if I'm a bit dense, but I'm not the brightest bulb on the Christmas tree sometimes.
hammie is offline  
Old December 30, 2018, 05:30 PM   #27
Nathan
Senior Member
 
Join Date: July 1, 2001
Posts: 4,616
There are several words in that diagram the need a circle instead of a line. Head is one where the entire base area could be circled...
Nathan is offline  
Old December 30, 2018, 07:14 PM   #28
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,238
mehavey is offline  
Old December 30, 2018, 07:41 PM   #29
HiBC
Senior Member
 
Join Date: November 13, 2006
Posts: 6,142
For the sake of understanding,hammie,the flat face of the breech is one important surface.
If you set a piece of brass vertical on the table,the case head is resting on the table.(I'll agree the "head" includes more,but for our immediate purpose,"headspace" think of the base surface)
In the gun,we might say the case head rests against the breech face.
But I say that with reservations.We'll talk about it more in a minute.

For now,think about the case head resting against the breech. That is one boundary for the brass.

There are different systems to establish the forward boundary for the brass.

One is a rim,like the 30-30 or 22 rimfire.

Another is the case mouth,like 9mm or 45 ACP.

Another is a belt,like most magnums.300 win mag is an example

another is the shoulder of a rimless case.Specifically,SAAMI gives a diameter,a theoretical ring that rests on the shoulder normal to the axis of the chamber.

In each case SAAMI gives a dimension from the breech face to the appropriate headspacing feature. The minimum and maximum acceptable dimensions from the breech to the headspacing feature are the headspacing dimensions A gunsmith worthy of working on a gun will use a set of headspace gauges ,a "Go" and a "No Go" to confirm the chamber is cut to the proper depth. The headspacing feature is precisely ground into the chamber reamer.

The chamber is cut to acceptable standard of HEADSPACE when the rifle chamber accepts the "GO" gauge and it does not accept the "NO GO" gauge.


That's it. That's headspace.Its all about the breech and the chamber of the firearm. We don't even have any ammunition. Note that there is a tolerance range of acceptable chambers.(We will save "field gauge" for another day...well,OK.Old guns or abused guns can wear and develop a longer headspace.There is an acceptable amount of wear before the gun should be taken out of service.If a gun accepts the "Field gauge" its a reject)


OK,but we want to shoot ammunition in our gun.The ammunition has a dimensional relationship with the rifle chamber. We have to control that,too.

We trust factory ammo to be right. SAAMI spec. It usually is.


That would be all most folks need to know,except for those pesky reloaders.If new ammo was fired once in SAAMI spec guns,and thrown away,we would not need to worry about all this barn carpet.


But reloaders use brass over again.They want the bolt to close,even if the brass was fired in a long chambered gun and stretched a bit. It might go in a short chambered gun. We want to minimize case stretch to make the brass last longer.

But only the gun has headspace. How do we reloaders talk about this? How do we help newbies with questions? Its not easy because A) You need help with "case head" (That's OK)


So now I will tell you,due to tolerances,the cartridge head does not exactly rest on the breech face when stopped up against the headspace feature.We try to make the ammo just a bit short.It might be .002,or .004,or .006 for the M-1/M-14.


We want a little CLEARANCE between the CASE HEAD and the BREECH FACE so the gun can lock up securely without interference.


Guess what the CLEARANCE btween the HEAD and the BREECH is called?


HEAD CLEARANCE


You want SOME.but not TOO MUCH.


How do we do that? There are several methods to measure and control it.


Its easier to do than it is to explain because I'm not allowed to use the words "Cartridge Headspace" as opposed to "Chamber Headspace",the difference being "Head Clearance"


And it seems every time someone asks,we re-write the whole discussion.


I don't know why.

Last edited by HiBC; December 30, 2018 at 08:03 PM.
HiBC is offline  
Old December 30, 2018, 07:50 PM   #30
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,238
Quote:
I'm not allowed to use the words "Cartridge Headspace"
as opposed to "Chamber Headspace"
Sure you are. . . . Add the word 'dimension' and Go for it.
(Columbus took a chance, and he died)
mehavey is offline  
Old December 31, 2018, 10:35 AM   #31
hammie
Senior Member
 
Join Date: March 18, 2009
Location: Temple, TX
Posts: 681
Thanks everyone. I get it now. The terminology threw me off.

At the first of this thread, I wondered why we were spending time on something so simple. Well...sometimes things are not as simple or obvious as they seem. This was fun and informative.
hammie is offline  
Old January 1, 2019, 02:21 PM   #32
RC20
Senior Member
 
Join Date: April 10, 2008
Location: Alaska
Posts: 5,687
Realy it is as simple as how the case fits in the chamber.

And I can change my head space from NO Go (and have ammunition that shoots fine) all the way to field reject (deponent on the gun, if its control round feed it will likely fire as its held in place by the extractor if is push feed then it will not (tested) as the case rim never engages and it just gets pushed into empty space)

Quote:
OK.Old guns or abused guns can wear and develop a longer head-space.
I disagree with that. You can eat the throat out but the chamber shoulder does not which would change the head-spsce.

The Model of 1917 Enfield (30-06 WWI for those not in the know) does push head-space to filed reject.

Many military guns have more generous chamber for combat conditions.
__________________
Science and Facts are True whether you believe it or not
RC20 is offline  
Old January 1, 2019, 03:37 PM   #33
HiBC
Senior Member
 
Join Date: November 13, 2006
Posts: 6,142
RC20,for the wear I was thinking more of 100 years of locking lug to receiver wear,or softer steel locking lug setback,or sustained overpressure loads.

Or even a mismatched bolt. But,I agree with you its unlikely a shoulder would erode to cause a reject.

Wartime standards? I'm thinking that's its own topic.In fact,I do not know what the QC was at the arsenal regarding GO vs NO GO chambers.I would GUESS/ASSUME they used the same 30-06 gauges.They also had 1917 steel,and 1917 eyeball heat treaters,too.The rifles lived in abrasive muck filled trenches,and were perhaps in two wars before we drop a field gauge in them and assume "sloppy wartime standards" I don't know.

I realize all sorts of strange things are done.I realize some folks headspace on the extractor. It goes "bang" . I don't do that. Its just another source of confusion for the person we are writing to help. YES!! If you put an 8x57 round in an 8mm-06 and shoot it...blah blah blah...supposedly one individual offers that as proof that …..blah blah.....I've read it too many times.

We also agree that a knowledgable handloader can make custom "workaround" ammo that ,from a "head clearance" standard,will work just fine in a rifle with out of spec headspace.We can load ammo with .002 head clearance for a rifle with .020 headspace. No problem!. But don't take that ammo hunting if you are shooting a different rifle.We have SAAMI standards so we can trust 30-06 ammo to work in 30-06 guns.


Nothing says we HAVE to follow SAAMI specs.

We might question what happened to cause the excessive headspace.Something moved if the rifle was properly chambered when new.

I had a woman friend with a Marlin 30-30.The fired brass showed the primer backed out about 1/32 of an inch. A mutual Old Guy friend had an eye for that 30-30. He put up some $ for a Savage 99 in .300 Savage I found for her.I put a used 4x Leupold on it It would shoot 2 MOA.She put venison on the table with it.

A Handloader can headspace the 30-30 on the fireformed shoulder rather than the rim IF the brass did not grow a stretch ring in the process. There are ways around that,too. That Old Man had the rifle in his truck and fired factory loads once. Done.

Last edited by HiBC; January 1, 2019 at 04:10 PM.
HiBC is offline  
Old January 1, 2019, 04:43 PM   #34
RC20
Senior Member
 
Join Date: April 10, 2008
Location: Alaska
Posts: 5,687
On the 1917 it was simply what they did. While 100 years old, the OEM barrels on the 0ones I have are new.

Keeping in mind the guns came out of E, R or W from a British design (Pattern 14) standpoint tech and they may have just followed that. I will have to check my JA barrel to see what its headspace is, I don't remember. Its a WWII 1903 barrel with 1917 thread and front sight base otherwise.

They followed the Brit 5 grove rifling as well as the twist direction. They did change the bore to match the US .308 standard though its a tad different on OEM due to the rifling type.
__________________
Science and Facts are True whether you believe it or not
RC20 is offline  
Old January 1, 2019, 05:52 PM   #35
mehavey
Senior Member
 
Join Date: June 17, 2010
Location: Virginia
Posts: 5,238
You can stretch an action -- just a few thousandths is all it takes -- and therein lies the headspace growth vulnerability.
But `ya gotta work at it . . .
mehavey is offline  
Old January 1, 2019, 08:58 PM   #36
stagpanther
Senior Member
 
Join Date: March 2, 2014
Posts: 5,650
The answer is pretty much right there in the 308 diagram mehavey posted.
__________________
I screw things up--so you don't have to.
I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!
stagpanther is offline  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 01:50 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2018 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.06061 seconds with 9 queries