Help me understand "Head Space"

At least with rimless bottleneck rifle cases, you can leave the case unresized and only resize the neck so it will grip the bullet. Since the case blew out to fit your chamber, you essentially have zero headspace from the second firing onward.

With rimmed cases, if you have excessive headspace, you are stuck with it. Some rimmed bottlenecks can headspace on the shoulder.

What is the consequence of too much head space? Short case life. I used to have a Ruger Super Blackhawk that ate up cases at a ridiculous rate unless I downloaded to .44 special plinking velocities. What happens it the case expands against the chamber walls gripping the chambers while the pressure pushes the case backwards against the breech. This movement stretches the case until the head separates. I would only get about 4 reloads out of brand new brass before this started happening, except with a batch of Norma cases which seemed to be immortal. I suspect they may have had thicker rims.

My current S&W Model 29 .44 Mag does not have this problem, cases last until the mouth splits.
 
Hornady reloading manuals explain headspace pretty well, although when you start to dabble into foreign and even US military chamberings there will be variations in spec call outs. Even MILSPEC brass is different. The military 30.06 and the .308 chamber specs are called from a different point than SAMMI specs are. Most of you may have noticed that the more recent load books have more than one section for the .308 cartridge. I would suggest reading a good reloading book. I have great respect for P.O. Ackley's writings, but in his Vol. I Handbook for Shooters & Reloaders, his explanation of rimless headspace is just wrong. It is a difficult thing to explain even if you understand it, which I am sure he did.
 
Some of you guys are being too tough on Mr Guffey. For a while, a long while, I just flat didn't understand much of what he was saying, but I could see that there was much knowledge and experience there. So I'd take a couple of Advil and focus real hard on converting what he said to a language I could understand. I'm getting there slowly and I am understanding much more of what he says. He makes a lot of sense (after translation). He isn't an easy read, but that's Ok. I like his perspective. It is different.

He may well think that there are idiots among us. He may be right.
 
When an 8mm57 is fired in an 8mm06 chamber the 8mm shoulder is .121" + clearance from the shoulder of the chamber. then there is the 'auto response' as in forum members condition to respond to trigger words and phrases. It always starts with the firing pin strikes the primer and the whole thing (bullet, powder and case) take off and collide with the shoulder of the chamber. Like the song "Along cam John", and then, and then the primer is crushed.
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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'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
 
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.
 
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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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.
 
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
 
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?
 
Then there is that .7854 thing,
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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
 
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
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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 .
 
I contend a bullet that jumps to the lands slows down if not stops when it hits the lands .
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"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
 
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
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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.
 
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 never said it was easier just that there is no secondary action/disruption to the bullet if the bullet is already in the lands .
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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
 
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.
 
That backs Mr Guffey's "running start".
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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 .
 
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test that suggested the bullet slows or does not accelerate equally
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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
 
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