Explaining Headspace

[Innovative]

Headspace is the clearance in your chamber between your case head and the breech. It can be measured in several different ways, and there's a different story for each type of cartridge. Some of the most popular cartridges are rimmed, non-rimmed and belted. Here's a good article (I wrote it) that explains headspace.

Understanding Headspace

Headspace is different to someone that's installing a barrel, and special go/no-go gauges are needed. Chamber clearance (at the shoulder) is also important for shooters that want to make quality handloads. However, the handloader uses different tools to measure the chamber clearance that his loads have in his particular chamber.

- Larry

[NEILT]

Originally Posted by Alpo

Headspace is the distance from the head of the cartridge to the face of the bolt. If there is not enough room, the gun won't function. The bolt won't close, or (in the case of a revolver) the cylinder won't turn all the way. This is "too little headspace".

When the cartridge is fired, before the bullet starts to move (remember the law of inertia - whatever is at rest tends to stay at rest, and the more mass it has, the harder it is to put into motion) the lighter brass case first expands out until it hits the chamber wall, and then it is slammed backwards until it hits the bolt (or, in the case of a revolver, the recoil shield). Once it has done that, the case can't move anymore, and the only thing that can move is the bullet, so it, finally, starts to move forward. If the distance between the head and the boltface (or recoil shield) is too great (this is referred to as excessive headspace) the case has farther to go before it stops, which allows it to build up more speed and more pressure before it hits, which can cause damage to the gun. Also, if the headspace is excessive, the firing pin may not be long enough to pop the primer, and you have misfires.

Cartridges "headspace" in different areas, depending on the design of the cartridge.

Rimmed cartridges headspace on the rim. That's why you can use both 38 and 357 in a 357 revolver. The 38's being shorter does not matter, since the rim is in the same spot on both rounds.

Belted magnums headspace on the belt. They work the same as a rimmed round, in that if the case is a little too short, it doesn't matter, since the belt is always in the same place.

Bottlenecked rimless rounds headspace on the shoulder. Like with the belted cases, it doesn't matter too much if the overall length is a little short, as long as the shoulder has not been blown forward or pushed back.

The last group is the straightwalled rimless cartridges. They headspace on the mouth. 45 ACP, 9mm, 40 S&W, etc. If you look in the chamber of most modern pistol rounds, you will see a little "step" in there. This gives the case mouth somewhere to sit. Without it, since the case is rimless, the entire cartridge could fall through the chamber. Because they headspace on the mouth, overall length of the cartridge is critical. Too long and the bolt won't close (too little headspace) and too short and the cartridge goes too far forward into the chamber (excessive headspace).

Some of the older revolvers don't have this step in them. The cylinder is bored straight through. There is no need for the step, since they headspace on the rim. Most modern revolvers have this step, though, but it is more of a safety issue than for headspace. The step will not allow you to chamber a 357 in a 38 special. Without the step, one might fit, with disastrous results.

Thanks for explaining that

[Edward Horton]

And excess headspace.

[jack404]

100% correct

all these fancy night clubs and such have way too much headspace ...

[madbuck22]

this thread has been informative and entertaining. I give it an 11.

[CampingJosh]

Edward, that's a great graphic! Thanks for adding to the thread.

[Edward Horton]

For you Enfield collectors and shooters.

Its not the headspace that gets you, its actually the "HEAD CLEARANCE" or the air space between the bolt face and the rear of the case that causes your cases to stretch. This applies to any type case, rimmed, rimless, belted etc.





Many people blame the Enfield rifle for short case life, the real problem is American commercial factory cases are not made to British military specifications. If any cartridge case is properly fire formed with the base of the case against the bolt face it will last much longer.

[madbuck22]

this might be a stupid ? how do u get the original head space back from your fired round is it when u put it through the re sizing die? or when u trim?

[CampingJosh]

No stupid questions, madbuck. We were all new at some point, and for some of us (me in particular) it was more recent than others.

Resizing a case will return it to the original exterior dimensions as though it had not been fired. This should cause the case to headspace correctly no matter how it does so (on the rim, the belt, the shoulder, etc.). However, if a case is too long, that case or a bullet seated into that case can cause problems with headspacing (among other possible issues).

So really, you need to both size and trim (if over max length) to make sure that previously fired cartridges be safe to use again.

Clear as mud yet?

[madbuck22]

k

[Edward Horton]

On a bolt action rifle you only need to push the shoulder back .001 to .002 when full length resizing.

A full length resizing die is designed to push the shoulder back .002 shorter than minimum headspace. If your actual headspace is .003 more than minimum headspace and you die is set up to make hard contact with the shell holder you will be pushing the shoulder back .005 or more. This will cause case head separations and short case life and could als effect accuracy.

Below simple ways to control and measure cartridge headspace.

[mw0248]

you guys need a little coaching here;
I'm talking about RIFLE rounds, but the same kinetic principle aplies to pistol, and revolver cartridges as well;
When the bolt of your rifle is locked, there is a 'head space', that distance between the back end of your round, and the bolt; Usually around .001-.002 of an inch;
When your round fires, the PRIMER actually moves back, and hits the bolt face;due to the round (the brass) expanding into the chamber dimensions of your rifle; a gas seal is formed when your brass expands into your chamber, and gess what? The only thing that can move is your PRIMER; and the bullet; The primer hits the bolt face, and sits there, waiting for the shell ( the brass) to decompress as the bullet goes down the barrel, and the PRIMER actually re-seats its self back into the spent shell;
This is what headspace is about; Too little headspace can't be measured; simply because, if your round wont chamber, it's not a headspace problem; It's a chamber broblem;
On the other hand, if you have a firearm that is shot out (neck/shoulder), this will allow
the unfired round to travel too far forward, thus creating a "HEADSPACE" problem, cause it allows the PRIMER to go too far back, allowing gases to escape behind the back of the brass case that you are shooting; This causes all kinds of problems, some of which can cause injury/death if not taken care of;

To an upcoming shooter, HEADSPACE can be confusing, but its just physics;

If you shoot a lot like I do, then you find these things out;

Lot easier now, than when we tried em out;

By the way, I have a SUPER .243 load with 95 gr. if you are interested (bulls eye at 200 yds);
Shoot well, and be safe!!
Mike

[mw0248]

when you 'full length' resize a shell, you stretch the shell FORWARD, cause thats the only way it can go; the brass thins as is it stretched and gets longer, causing it to get thin; then you get split cases, due to pressure more than the thin case can take; and you also end up trimming them for being too long;

The above mostly applies to autoloaders;

If you shoot a bolt action, or lever action rifle, dont full length re-size your cases;

just collet size them for the neck size of the round you are shooting; you have a perfectly sized shell for your rifle; and your cases will last ten times longer;

From LEE 2ND EDITION RELOADING MANUAL

[passagenight]

Ok, understood; I think...but I have a Marlin 1895 and a Ruger #1 both chambered for the 45/70. I reload, and have done so safely so far. These are rimmed cases of course which would define the headspace as being almost immaterial?.......but some rounds will chamber in the Marlin and will not chamber in the Ruger. The difference seems to be the 'taper' of the bullets used. If tapered the Ruger will chamber; if 'rounded' it hangs up just in front of the rim. Of course I don't force this.
Is this a case where the bullet is engaging the rifleing of the barrel on it's curvature?

[howlnmad]

Originally Posted by passagenight

Ok, understood; I think...but I have a Marlin 1895 and a Ruger #1 both chambered for the 45/70. I reload, and have done so safely so far. These are rimmed cases of course which would define the headspace as being almost immaterial?.......but some rounds will chamber in the Marlin and will not chamber in the Ruger. The difference seems to be the 'taper' of the bullets used. If tapered the Ruger will chamber; if 'rounded' it hangs up just in front of the rim. Of course I don't force this.
Is this a case where the bullet is engaging the rifleing of the barrel on it's curvature?

It sure sounds like that's your problem. Are you seeing marks from the rifling on the round nose bullets?

[scansat]

Excellent explanation. I've always wanted a more detailed explanation and this thread hit the nail right on the head!

[mgrove4758]

AMEN

[BlackEagle]

Originally Posted by mgrove4758

AMEN

Welcome to the forum, mgrove. You've found a great place to listen, learn, and hang out and chat and laugh.

What do you shoot?

Are you into reloading?

[howlnmad]

Those shims in post #36 look like a great idea but you can acomplish the same thing with a set of feeler gauges.

[oneidapj]

Originally Posted by mw0248

when you 'full length' resize a shell, you stretch the shell FORWARD, cause thats the only way it can go; the brass thins as is it stretched and gets longer, causing it to get thin; then you get split cases, due to pressure more than the thin case can take; and you also end up trimming them for being too long;

The above mostly applies to autoloaders;

If you shoot a bolt action, or lever action rifle, dont full length re-size your cases;

just collet size them for the neck size of the round you are shooting; you have a perfectly sized shell for your rifle; and your cases will last ten times longer;


From LEE 2ND EDITION RELOADING MANUAL

I am just about ready to load my first,,, I think. Something always comes up new that I need to know more about before I start. Now I am waiting to get a case re-sizer because all the brass I have collected over the years (shot only once, some twice) are different length, from 2.484 to 3.000 and the Nosler book says max is 2.494. Now mw0428 says we don't need to length size them??? We both have bolt action 30-06. Mine is a very old BSA? and hers is new Mossberg.

For myself I bought Nosler partition spitzer 180 grain and my wife Hornady 165 grain sst (which has the groove around the bullet, the Nosler one doesn't). Do these need some kind of crimp? If they do then the instruction are to re-size all brass to the same length. And if length is know big deal won't the mouth of the brass at some point stretch enough to hit a step in the barrel?

One more question is- should I keep my brass seperate form my wifes' in the future for reloading?

Dennis

[Alpo]

You've got a half-inch difference in the length of your brass? I think you typed some numbers wrong.

First, ignore that comment about "if you shoot a lever, don't full-length resize". That's nonsense. You can get away with neck-sizing on a bolt gun or a single-shot, but anything else needs full-length resized.

Second, you can only get away with neck-sizing if it is going to be shot in the SAME GUN. If you have ONE 308 bolt gun, and you fire new shells in THAT 308 bolt gun, then the brass is fire-formed to THAT chamber. You can then neck-size the brass that will be loaded to be fired in THAT gun. There is no other gun in the world that has that exact size chamber. NONE. NOWHERE. So if you neck-size brass shot in THAT 308 bolt gun, and then try to put the loaded ammo into THIS 308 bolt gun, there is a good chance that it will not fit.

Now, as I understand your post, the brass you have is stuff fired in YOUR gun, stuff fired in YOUR WIFE'S gun, and stuff that has been given to you or that you found at the range. In other words, NOT ALL FIRED IN THE SAME BOLT GUN OR SINGLE SHOT. It needs full-length resized.

Once it has been full length resized, it will fit in any gun of that caliber. If you plan to neck-size after that original full-length sizing, definitely keep your brass separated from your wife's brass.

If your gun is NOT a bolt or a single-shot. If it is a lever, a pump or an automatic, ignore anything anyone tells you about the joys of neck-sizing. It will just cause you pain and heartache, trying to make it work.

[oneidapj]

Thanks Alpo,

My mistake at just learning to read my dial caliper... the lengths range from2.484 to 2.500.

Yes the brass I have is from different guns but nothing from the range, don't want to risk getting bad stuff. So what I planned to do was tumble the brass, run it into the die to full-length resize, decap it, inside neck expand, trim all brass to same length (if I need to crimp them) or at least trim them to the spec of 2.494 that the Nosler book says (if I don't need to crimp them), tumble again, prime, powder charge, bullet seat.

Maybe there is something I am totally not understanding. OK.... Full length resizing means returning the brass to the original new brass size, except for overall length. And neck-sizing just spreads neck big enough to accept and hold the bullet. Nooowww, doesn't the neck-expanding part of the die open every case to the exact same diameter? So why would do you say that if I plan to neck-size after the full-length sizing keep our brass seperate?

From what I have read so far about crimping... I don't need to crimp.? Maybe I should put a light crimp on the rounds we are going to actually pack around hunting. But if I do that,shouldn't lightly crimp them all to make it all all the more consistant?

[Alpo]

No, neck sizing is squeezing the neck down.

Your bullet is .308. The diameter of the bullet-section of the chamber of your rifle is gonna be something like .350. Let's say your brass is .015 thick. That means you got a 308 bullet with 015 on each side of it, making a total of 338 diameter. There must be some room for the brass to expand to release the bullet. so let's say that the bullet section of your chamber is 350.

You fire the gun, the case expands until it hits the chamber walls and the released bullet goes downrange. Now your fired case has a neck OD of .350, and since the walls are .015, the ID is .320. You put a 308 bullet in that 320 neck and it will fall back out.

So you need to squeeze the neck down, so that the ID is about 306, so when you shove that 308 bullet in there the neck holds it tightly.

The case body, which started at .441, has expanded to .460. The shoulder, which started at 1.948 is now at 1.953. It is now "fire-formed" to fit the chamber of THAT gun. When you full-length resize a case, it squeezes the body back down to .441 and pushes the shoulder back to 1.948, along with squeezing the neck do to an ID of .306.

When you neck-size, it does nothing to the body or the shoulder of the case.
All it does is size the neck back down to that 306 ID.

A cartridge that is loaded into a case that has been full-length resized will fit into any 30/06 rifle.

A cartridge at has been neck-sized will only fit easily into the gun it was fire-formed in.

[Alpo]

In reloading, "sizing" always means "squeezing smaller". It's short for "resizing". Making the neck of the bullet big enough to accept the bullet is "expanding". First you "size" it, which makes it undersize, and then you "expand" it, which makes it big enough.

[oneidapj]

I'm trying to grasp this with what I want to do.

What are your thoughts of crimping these bullets that I bought, or not? Basicaly we are going to be doing a bunch of target shots, but with intent of a good hunting kill shot.