Headspacing belted magnums

[223Rem]

IIRC, belted magnums are headspaced off the belt and not the shoulder. However is it possible to adjust the headspace so it falls on the shoulder?

Plans are to lengthen the life of the brass by doing so, accompanied by neck sizing.

TIA

[Ray Gunter]

For Belted Magnums
You could just use brass fired in that gun and when re-sizing set the die so that it does not bump the shoulder back.

Now you have rounds that will headspace on the shoulder of your chamber. And without ever unscrewing the barrel.

Plus you can still fire factory rounds.

[bigedp51]

It doesn't matter how a cartridge case headspaces, the only difference is the distance from the bolt face to the datum line.

http://i122.photobucket.com/albums/o254/bigedp51/Headspace_2_lg.jpg
http://i122.photobucket.com/albums/o254/bigedp51/Headspace_1_lg.jpg

Step one, get a neck sizing die
Step two, never push the shoulder back shorter than .001-.002 than actual chamber length at the shoulder of the case with a full length resizing die.

Pretend the .303 cartridge below is a belted cartridge. (or any type case)

http://i122.photobucket.com/albums/o254/bigedp51/headspacestretch-1.gif

When "ANY" cartridge case is properly fireformed it can headspace on the shoulder without stretching and thinning in the web area of the case.

http://i122.photobucket.com/albums/o254/bigedp51/fireformed-zeroheadspace.jpg

Again pretend below that this is any type cartridge case, insert a spent primer in the primer pocket and chamber the case in your chamber and eject the case. The amount the primer is protruding from the base of the case is how much head gap clearance you have. In the photo below the amount of exposed primer is how much the case will stretch when fired. (air space between the bolt face and the rear of the case)

http://i122.photobucket.com/albums/o254/bigedp51/9.jpg

By seating your bullets long and jamming them into the rifling when fireforming your case it will be held against the bolt face and not stretch when fired.

What you need is a good old British .303 with excess headspace, all you need is a rubber o-ring to hold the case against the bolt face. ;D

http://i122.photobucket.com/albums/o254/bigedp51/IMGP5098.jpg

You fool the rifle into thinking the rim is much thicker and the case does not stretch.

http://i122.photobucket.com/albums/o254/bigedp51/headspacestretch_frame_0001.jpg

NOTE: On the Enfield rifle with American made cases you can have .016 head gap clearance and still be within military headspace requirements.

[223Rem]

That was one hell of a primer, Thanks!

[scratcherky]

Headspace is not the distance from the bolt face to the datum line as the diagrams depict! Headspace is the amount (measured in thousanths of an inch) that the cartridge is free to move in the chamber with the bolt closed.

[bigedp51]

scratcherky
Headspace is not the distance from the bolt face to the datum line as the diagrams depict! Headspace is the amount (measured in thousandths of an inch) that the cartridge is free to move in the chamber with the bolt closed.

Then what would you call head gap clearance..................

As an example if the rim thickness on a .303 British is .058 and the headspace is set at .067 you have .009 head gap clearance. (air space between bolt face and rear of case)

.058 + .009 = .067

Headspace isn't what causes the case to stretch, the head gap clearance or air space does.

On the Enfield rifle with its rear locking lugs and a case in the chamber you can measure head gap clearance with a feeler gauge. Add the head gap clearance to the rim thickness and you have the actual headspace measurement.

Below on the left white arrow is the Enfield receiver, on the right arrow is the locking lug, the air gap where the feeler gauge fits is head gap clearance.

http://i122.photobucket.com/albums/o254/bigedp51/IMGP6598b.jpg

http://i122.photobucket.com/albums/o254/bigedp51/IMGP6600.jpg

My Stevens 200 headspace is .002 longer than GO or minimum headspace, some brand new unfired cases were .009 shorter than GO or minimum headspace. If these short cases are not fire formed properly they can stretch .011 when fired.

On any fireformed case the rear of the case is touching the bolt face, you have zero head gap clearance and the case can NOT stretch in the web area when fired.

Watch the animation below, watch the primer move to the rear and then watch the case stretch in the web area. Its the head gap clearance or air space that does the damage to your cases when fired.

http://i122.photobucket.com/albums/o254/bigedp51/f55-movie-dsf1.gif

[scratcherky]

I respectfully disagree. In your example of .058 + .009 = .067, the .009 is headspace not head gap as you call it. Again headspace is the amount the round is free to move with the breech closed. The datum is used to measure headspace and varies with type of round. See the link below. The gun depicted is break action but that makes no difference in what head space is.

http://www.youtube.com/user/ThompsonCenterPros#p/a/u/2/wRWW43Tflgw

[bigedp51]

scratcherky

You can then respectfully disagree with the SAAMI

Example:
30-06 SAAMI headspace limits
2.0487 = GO
2.0587 = NO-GO

Below at the circled X (headspace dimensions) 2.048 min - 2.058 max

http://i122.photobucket.com/albums/o254/bigedp51/saami30-06.jpg

Anyone with two fingers and a computer can say anything they like on the Internet BUT that doesn't make what they say correct, factual or even in the ball park. The feeler gauge used was based on the rim thickness of "THAT" 45-70 case and another brand could have been thicker or thinner.

Below the Remington .303 case on the left has a rim thickness of .058 and the South African military case on the right has a rim thickness of .062. The difference in the size of the feeler gauge between these two cases would be .004 and that doesn't change the actual headspace of the rifle I fired these cases in at .067.
(but it will change the head gap clearance)

http://i122.photobucket.com/albums/o254/bigedp51/thicker-3.jpg

Now please look below in the upper left hand corner of the SAAMI dimensions for the .303 British and rim thickness tolerances. Rim thickness maximum .064 -.010 this means the manufacturing tolerances for the rim can be from .064 to .054 and the average American rim thickness is between .060 and .058

http://i122.photobucket.com/albums/o254/bigedp51/303saami.jpg

I have headspace gauges and I have gauges to check cartridge headspace lengths.

http://i122.photobucket.com/albums/o254/bigedp51/IMGP7241.jpg

And I don't respectfully disagree with my gauges or the headspace limits set by the SAAMI.

[Tbob]

Headspace is the distance between the back of the case head and the bolt face, when the cartridge is fully inserted into the chamber. If you take a rimmed cartridge that headspaces off of the rim, and you change that rim thickness, you will change the headspace. It has to. You are either taking up or adding space between the cartridge head and bolt face when you do this. This head gap measurement you refer to in one point of your post is headspace.

[bigedp51]

Tbob
Headspace is the distance between the back of the case head and the bolt face, when the cartridge is fully inserted into the chamber. If you take a rimmed cartridge that headspaces off of the rim, and you change that rim thickness, you will change the headspace. It has to. You are either taking up or adding space between the cartridge head and bolt face when you do this. This head gap measurement you refer to in one point of your post is headspace.

WRONG

Both you and scratcherky need to Google headspace until the light bulb goes off.

Head gap clearance is the distance from the bolt face to the rear of the case, and this is the "air space" measured with the feeler gauges. When you fireform your cases to "your" chamber you have zero head gap clearance and the headspace measurement remains the same before firing and after firing the case.


Go back up and read the 30-06 headspace limits

2.0487 GO or minimum headspace
2.0587 NO-GO or maximum headspace

2.0456 is minimum cartridge length from the rear of the cartridge case to the datum line on the case
2.0526 is maximum cartridge length from the rear of the cartridge case to the datum line on the case

If the headspace is 2.0587 and the cartridge case is 2.0456 you have .013 head gap clearance.

Headspace is not head gap clearance

You have minimum and maximum case length tolerances

http://i122.photobucket.com/albums/o254/bigedp51/rimless.jpg

And you have minimum and maximum chamber headspace tolerances

http://i122.photobucket.com/albums/o254/bigedp51/Headspace_2_lg.jpg

And when you have a negative or shorter cartridge case length than actual headspace length measurement reading you have head gap clearance.

[rsbhunter]

You guys have alot more technical info than i do, but if "headspace" isn't the distance between the datum line and bolt face, why would headspace be set by installing the headspace gauge/ or a new full length sized (not with the shoulder bumped) brass case, and then screwing the bbl on til it stops.In effect, it is the head of the case , hitting the face of the bolt. Thus , the measurement is from the case head, to the datum line (where the shoulder contacts the shoulder area in the chamber), if that space is more than SAMMI specs (longer) then excessive headspace is created, so it doesn't matter whether it is rimmed, rimless, or rebated rim.......but i wonder if the belted cases headspace is the distance from the front face of the belt to the head of the case...you would think that it would be a standard measurement for EVERY belted case, as if the belt to case head isn't exact on EVERY case, it effectivily creates an excessive or no go headspace condition, wouldn't it?....rsbhunter

[bigedp51]

One more time as simple as I can put it......


























Excess headspace


http://i122.photobucket.com/albums/o254/bigedp51/10_foambeer_lgl.jpg


And too much head gap clearance kills your brass.


http://i122.photobucket.com/albums/o254/bigedp51/308fail.jpg

http://i122.photobucket.com/albums/o254/bigedp51/308fail-2.jpg

These cartridge cases were full length resized which created too much head gap clearance and the cases kept stretching in the web area until they cracked and failed. Headspace didn't kill these cases but head gap clearance did and that is the air space between the bolt face and the rear of the cartridge case.


Below, acceptable headspace but very near field max, BUT I have one other cartridge waiting to be checked for headspace.

http://i122.photobucket.com/albums/o254/bigedp51/IMGP2800.jpg

[Con]

bigedp51,
Just a side note ... do you believe the SAAMI chamber dimensions for the 303British to be true of the British military and commercial rifles that were chambered to this cartridge?
Cheers...
Con

[bigedp51]

Con
Just a side note ... do you believe the SAAMI chamber dimensions for the 303 British to be true of the British military and commercial rifles that were chambered to this cartridge?
Cheers...

No the British military chamber was created before the SAAMI was instituted in 1926 and even the much later European CIP standards. The European CIP lists the .303 British as having problematic headspace defined by depth of rim recess or too much headspace.

Additionally the British military chamber was lengthened to accommodate the mud of Flanders early in WWI.

Below a .303 British cartridge case fired in a lengthened military chamber, resting on its shoulder in a American SAAMI Wilson case gauge. The amount seen above the top of the gauge is how much longer the military chamber is than SAAMI dimensions.

http://i122.photobucket.com/albums/o254/bigedp51/IMGP6321.jpg

The British chamber is so much longer than the SAAMI chamber dimensions, a case forming and file trim die can be used as a shoulder bump die to push the shoulder back. The .303 case below will fall out of the case forming die by just hold the die upright.


http://i122.photobucket.com/albums/o254/bigedp51/IMGP7098.jpg

[scratcherky]

Tbob hit the nail on the head and understands headspace.! He is absolutely correct. If you change the rim thickness you change headspace plain and simple. Likewise if you change the measurement from case head to datum on a rimless case you change headspace.

[Con]

bigedp51,
Longer and with much more heavily radiused shoulder. I shared a phone call a few months back from a gentleman heavily involved in trying to produce No4 barrels. Anyway ... conversation led to a discussion on the chambers and he'd managed to source an original chamber print from the Lithgow (I'm in Australia) factory. Chalk and cheese ... compared to the SAAMI specs. That the chambers were long also begs the question, has the brass perhaps also deliberately been made shorter to assist function under battlefield conditions. ???

Anyone trying to shoot and maximise case life in 303British rifles ends up learning pretty quickly about the relationships between chamber, brass case and reloading die. ;)
Cheers...
Con

[bigedp51]

scratcherky
Tbob hit the nail on the head and understands headspace.! He is absolutely correct. If you change the rim thickness you change headspace plain and simple. Likewise if you change the measurement from case head to datum on a rimless case you change headspace.

You have chamber headspace given in a plus or minus measurement, or GO and NO-GO.
You have manufacturing tolerances for how long the cartridge case can be after it is made which is not called headspace.

These are headspace gauges for the .303 British.

http://i122.photobucket.com/albums/o254/bigedp51/IMGP5264.jpg

And the amount the primer is sticking out below is called head gap clearance.

http://i122.photobucket.com/albums/o254/bigedp51/9-2.jpg

If what you said was true then all headspace would be the same.
Did the .308/7.62 cartridge below have a head gap clearance problem or a headspace problem.
(Houston we have a problem)




http://i122.photobucket.com/albums/o254/bigedp51/image006e.jpg

http://i122.photobucket.com/albums/o254/bigedp51/762natoin3006.jpg

[bigedp51]

bigedp51,
Longer and with much more heavily radiused shoulder. I shared a phone call a few months back from a gentleman heavily involved in trying to produce No4 barrels. Anyway ... conversation led to a discussion on the chambers and he'd managed to source an original chamber print from the Lithgow (I'm in Australia) factory. Chalk and cheese ... compared to the SAAMI specs. That the chambers were long also begs the question, has the brass perhaps also deliberately been made shorter to assist function under battlefield conditions. ???

Anyone trying to shoot and maximise case life in 303British rifles ends up learning pretty quickly about the relationships between chamber, brass case and reloading die. ;)
Cheers...
Con



Below is a pre WWI drawing of the cartridge and chamber, during WWI the chamber was lengthened and the cartridges remained the same.

http://i122.photobucket.com/albums/o254/bigedp51/303deawingjpg.jpg

As you can see below the neck of the case was not formed until the cordite powder was placed in the case, and the glazed disk on top of the powder.

http://i122.photobucket.com/albums/o254/bigedp51/caseforming.jpg

http://i122.photobucket.com/albums/o254/bigedp51/216ab-1.jpg

Below, a new unfired case on the left and fired cases center and right and the effects of using a American SAAMI resizing die on commercial cases not designed to British military specifications.

http://i122.photobucket.com/albums/o254/bigedp51/IMGP0737.jpg

[scratcherky]

The link below explains headspace!
http://www.bellmtcs.com/store/index.php?cid=172&

[Tbob]

Biged, I will concede that we are all three right. After much research both on the net and in my reloading books I have here at home, I have headspace referenced or defined both ways.

Speer Reloading Manual #11
Glossary of Terms
Headspace

1. The distance from that surface of the barrel or chamber that positions the cartridge and prevents its forward movement into the chamber, to the face of the bolt or breech block, when the latter is fully back against its supporting surface. This is the most important dimension governing the safety of the shooter.

2. In handloading, the combination of cartridge case and gun must be considered when talking of headspace. To the handloader, a more useful definition of headspace is the linear endplay of a cartridge in the chamber, with the bolt closed. To the handloader, no gun need have excessive headspace, since he can adjust the cartridge case to fit the chamber, even though the chamber may have excessive headspace when measured by SAAMI standards.

Nosler Reloading Manual #3
Glossary of Terms
Headspace

1. In handloading, the slight gap that is permitted between the bolt face and the case head to facilitate closure of the bolt.
2. Headspace is actually the distance between the bolt face and that part of the chamber thatactsas the cartridge stop.

Sierra Rifle and Handgun Reloading Data Edition 5 2nd Printing
Glossary of Terms
Headspace

1. The amount of play between the case head and the breech face, in a fully closed action. Insufficient headspace will cause difficulty in chambering, while excessive headspace will result in head separations. Headspace problems may be the fault of either the gun, the ammunition, or a combination of both.

www.saami.org
Glossary
Headspace

1. The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats.

Head Clearance
1. The distance between the head of a fully seated cartridge or shell and the face of the breech bolt when the action is in the closed position. Commonly confused with headspace.



I have not found any reference to head gap clearance but understand you are actually referring to head clearance.

Again, headspace has been defined in multiple publications as being both what your definition is and what my definition is.

If nothing more, I learned that there is another definition of headspace, and next time this arises, I will be more educated. That's what these forums are here for......to learn.

I can live with that.