Help me understand "Head Space"

[F. Guffey]

I'm pretty sure that the inertia of the cartridge is enough to allow the firing pin to crush the primer, especially with the speed of a typical bolt action firing pin.
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My firing pins are killer firing pins, they crush the primer before the case, powder and bullet know their little buddy, the primer, has been crushed.

F. Guffey

[Gunplummer]

I stupidly did something like that once. I had 2 identical Arisakas with the exception of one being recut to a 6.5x55. I had more than one box of ammo on the table and reached over (Without looking) and put a 6.5x50 cartridge into the 6.5x55. The extractor held the cartridge to the bolt face and it fired. All I noticed was a lighter recoil. The case had stretched about .200 and formed to the chamber with a new shoulder and a short neck. The primer looked fine. Point is, if the primer is struck hard enough, the case will expand faster than the the case can be pushed forward.
I will toss out this example of the "Other headspace". Maybe we should call it "Side space". I was at the range one day and someone next to me put a .300 Savage into a 7.62x54R Russian rifle. (Same thing, couple boxes on the bench). He noticed the light recoil right away. We looked at the .300 case and it looked the same as the other cases that were fired IN a .300 Savage. This was factory ammo and probably loaded on the low side. I never checked it out, but by eye, the shoulder length on BOTH the .300 and Russian look really close. It would be a chore to check this out because both have a different headspace points. Maybe the headspace was OK, but the "Sidespace" could not have been. On occasion, I have made new bolts to correct a headspace problem when setting back the barrel was not an option. I remember one rifle where I got the headspace nice and tight, but still had a lot of case stretch (Sideways). I suspect the reamer was O/S at the factory. This is not uncommon with rimmed cases, as the case dimensions are locked into the rim on most reamers. Anyway, it was plenty safe to shoot, but the longevity of the brass to reload was reduced.

That is enough for one morning. I better switch to DeCaf.

[44 AMP]

I'm pretty sure that the inertia of the cartridge is enough to allow the firing pin to crush the primer, especially with the speed of a typical bolt action firing pin.

I disagree. Something has to hold the case "in place", I don't think inertia alone is enough. This is going to be either what ever point the case "headspaces" on, OR is going to be the extractor, in most cases.

Also, the inertia of a round is going to vary with the mass of the round.
Smaller cases are going to have less inertia.

The pressure of a firing pin (or hammer) spring is measured in pounds, often over a dozen pounds. A loaded round weighs what? less than an ounce, usually. I just don't see inertial alone holding the case in place long enough to crush the primer.

[F. Guffey]

44 AMP,

1 ounce = 437.5 grains.

There are 7,000 grains in a pound.

Then there is that .7854 thing, I have killer firing pins. Then there is that thing about millage. And there are variables, and there is that very boring conversation that starts with "Hatcher said".

Forgive, there are factors.

F. Guffey

[B.L.E.]

The firing pin of a AR-15 weighs about 120 grains. There are titanium firing pins available that only weigh 70 grains.
A .223 round with a 60 grain bullet weighs about 180 grains.

Now, if that 120 grain, or even a 70 grain titanium firing pin can crush the primer with its inertia, why can't a 180 grain cartridge have enough inertia to act as an anvil?

The spring does not push the firing pin into the primer. It's not nearly strong enough. Prove it to yourself. Chamber a primed case in a bolt action rifle. Lower the firing pin by holding the trigger back as you slowly close the bolt. Open the bolt. Do you see a dent in the primer?

[F. Guffey]

Then there is that .7854 thing,

I am the fan of the running start, I want my bullets to have 'the jump', I do not want my bullet setting still at the rifling, I do not want my bullet setting there wondering if it is going to start moving, I want my bullets moving into the rifling before it knows it is there.

It was suggested I was wrong, seems someone Velcro-ed a case into a large chamber, closed the bolt and then pulled the trigger.

F. Guffey

[Metal god]

I am the fan of the running start, I want my bullets to have 'the jump', I do not want my bullet setting still at the rifling, I do not want my bullet setting there wondering if it is going to start

I've never understood this point ????? As soon as the cartridge is chambered the bullet is just sitting there until it's not . It's not wondering what to do .

I contend a bullet that jumps to the lands slows down if not stops when it hits the lands . Hmm that to me would be when the bullet looks back at you and asks "a what now" . Unlike a bullet jammed in the lands . If the bullet never hit a resistance point in the firing process like running square into a smaller section to squeeze into it never gets a chance to think what it's supposed to do next . It just continually goes faster and faster never getting a chance to rethink it's objective .

Now I'm in no way saying one is better then the other . Only that when jumping a bullet to the lands . That creates a secondary effect on the bullet that does not happen if the bullet is already in the lands .

[F. Guffey]

I contend a bullet that jumps to the lands slows down if not stops when it hits the lands .

"jumps to the lands slows down if not stops when it hits the lands"

Jumps, slows down or stops? All that in milliseconds while the powder is burning and building pressure. And then? After stopping and or slowing down it has to start moving again.

F. Guffey

[F. Guffey]

Now I'm in no way saying one is better then the other . Only that when jumping a bullet to the lands . That creates a secondary effect on the bullet that does not happen if the bullet is already in the lands

If it is already there why is it easier to get the bullet moving if the bullet is jammed into the rifling? Pressure must build to get it moving, the secondary effect will be higher.

Again, I am the fan of the running start.

F. Guffey

Same thing with the firing pin. My firing pins have the running start.

[Metal god]

I never said it was easier just that there is no secondary action/disruption to the bullet if the bullet is already in the lands .

[F. Guffey]

I never said it was easier just that there is no secondary action/disruption to the bullet if the bullet is already in the lands .

I have heard that, I have always said anyone that believes that has never seen a graph that reads pressure and time as in 'when it happened' and the amount of pressure created 'when it happened'. The horror story begins when the bullet stops or 'really' slows down. To get a picture of that chamber an 8mm57 round in a 30/06 chamber.

Then there was the shooter that purchased 308 Winchester ammo for a 25/06 chamber. That was in central N. Texas. He was going to sue everyone.

F. Guffey

[603Country]

Consider that Weatherby cartridges require a freebore to keep pressure from spiking to dangerous levels. That backs Mr Guffey's "running start". I do not and will not knowingly jam a bullet into the lands when it's chambered. You can if you want to.

[Metal god]

That backs Mr Guffey's "running start".

I'm not sure what that is backing ? He just said he likes a running start . So do I and that was not my point . My point was VERY narrow in scope . Maybe I used the wrong term when saying the bullet slows down . Maybe a more accurate term would be that the bullet does not continue to accelerate evenly when it hits the lands .

Now it's been a couple years but I do remember reading a study or test that suggested the bullet slows or does not accelerate equally when it hits the lands from a jump . I'll try to find it .

[F. Guffey]

test that suggested the bullet slows or does not accelerate equally

I pull the trigger, after that it is out of my hands and I do not have a problem accepting the things I can not change. I do understand the things I am in control of before I pull the trigger.

There is nothing about pulling the trigger on a round with the bullet seated into the lads that impresses me. Then there is that other often repeated story about the firing pin driving everything to the front of the chamber. If the bullet is stuck into the lands and then the firing pin drives it further after the primer is struck the bullet is more stuck?

Or the bullet is driven back into the case, and that presents another problem with pressure, seating the bullet back into the case increases pressure.

F. Guffey

[Metal god]

Yep

[gwpercle]

I thought head space was the area under your hat !

[sirgilligan]

This is the way I think about it.

A cartridge can only go so far into an open chamber. Imagine you take your gun apart (it's easy with a pistol) and you have the chamber in your hand and you drop a cartridge into the chamber. It will only go so far because something stops it from going too far in. On some rifle cartridges like a .223 REM or .30-06 it is the shoulder of the case, thus I have heard people say that those cartridges head space off of the shoulder. Now, I don't know if they should say it that way, but I hear it all the time. A .22 Long Rifle stops going in when the rim of the cartridge contacts the ledge in the chamber. A 9 mm stops going in when the edge of the case mouth (right next to the bullet) contacts an edge inside of the chamber.

All of that to describe dropping a cartridge into an open chamber. Now let's close the chamber so to speak. In a bolt action rifle, that would be closing the bolt. Now remember the head of cartridge is the end where the primer / makers mark / caliber are located. Once closed, the head space is the distance between the closed bolt's face and the head of the cartridge. A perfect fit would mean there is no space, the bolt's face is touching the head of the cartridge.

Now imagine a .223 cartridge where it was resized incorrectly and the shoulder was mashed down from the case mouth towards the case head. Now, when you drop this cartridge into the chamber and close the bolt there is a space between the bolt's face and the case's head. At some point too much space between the bolt face and the case head become an issue.

Imagine a 9mm cartridge where the case was trimmed too much and now the case / brass is shorter than it should be. When it goes into the chamber and the slide closes there is space between the case's head and the breech face.

That is the way I think about it.

[Metal god]

Once closed, the head space is the distance between the closed bolt's face and the head of the cartridge.

NO ! that is incorrect . Using your analogy , head space is the distance from the bolt face to where the cartridge was stopped from going in any further . 223 bolt to chamber shoulder , 9mm bolt to ridge in chamber that the case mouth stops on , 22lr is the same as all rimmed cases . This measurement ONLY pertains to areas in the chamber or between the bolt face and where a rimmed cartridge stops and has nothing to do with the cartridge it self . So on a 223/30-06 the head space would be the distance from the closed bolt face to the area of the CHAMBERS shoulder where the case would have stopped . This area of the chambers shoulder is the datum line/area . There is no line but many say line when referring to this area .

[sirgilligan]

Then what is the space between the case head and the bolt face called?

Am I missing something? I don't know.

I am talking about reloading, not setting up a rifle or re-barrelling a rifle. This means that I am working with a rifle that has been properly setup and has had the space measured from the bolt face to the point in the chamber that is used for stopping the forward motion of a cartridge.

If you resize your case incorrectly and push the shoulder back to far, what have you messed up? The head space? So, again, what is it called when you do this? The space between the bolt face and the head of the case, what is that called?

[603Country]

Go back to the first part of this discussion and read what UncleNick said. Or read the Port-a-pottie analogy.

[Metal god]

Then what is the space between the case head and the bolt face called?

haha , with out trying to sound to snarky .

Its called the space between the case head and the bolt face

[HiBC]

How about head clearance?

[sirgilligan]

LOL.

Here is why I said what I said, I have two reloading manuals. Speers #14 and Hornady 8th.

From Speers, page 87:

"Remember that most bottleneck cases headspace on the shoulder. With the proper die setting, the shoulder will not be pushed back past its original position. Pushing the shoulder beyond this point will create excessive headspace."

From Hornady page 15:

"As the firing pin strikes, it moves the case forward to contact the front of the chamber, giving a little headspace -- but not a dangerous amount."

So, with all of the statements that head space is the distance between the breech face and the point in the chamber used to stop the forward travel of a case and that it is fixed is contradicted by the statement that you can create headspace from these two reloading manuals.

The Hornady manual shows a picture of the gap between the bolt face and the case head and indicate that to be the created head space.

So, if it can be created by setting the shoulder back too much, then the cartridge does have something to do with it.

If one thing is for sure in my mind, the term is used in two different ways in my reloading manuals.

[sirgilligan]

Here is an online resource, for those that don't have the same manuals. The author designates two types of head space. Chamber headspace and cartridge headspace length.

http://www.massreloading.com/bottlen..._resizing.html

Before we get into setting up the sizing die, we need to discuss headspace and cartridge headspace length. Headspace in a firearm is defined as the distance from the breech or bolt face to the part of the chamber that stops the forward movement of the cartridge when it is inserted into the chamber... The cartridge headspace length is the distance from the case head to the part of the case on which the cartridge headspaces...

The difference between the chamber's headspace and the cartridge headspace length determines the amount of extra fore-and-aft 'room' the cartridge has in the chamber... Too much room (because the cartridge headspace length is too short for the chamber) can result in inconsistent ignition, poor accuracy, short brass life, or catastrophic case head separation. In other words, if you get the cartridge headspace length wrong, the ammo will not shoot at all, will shoot badly, or will blow up. Therefore, it's quite important to get the cartridge headspace length right.

[sirgilligan]

Here is another online article that I just "re-found". I read it a while back.

http://www.larrywillis.com/headspace.html

"The term headspace means the "space" between the "head" of your case and the breech. This space (clearance) is set when your barrel is installed. Handloaders should minimize the chamber clearance that their handloads have in their chamber."