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Explaining Headspace

75K views 90 replies 50 participants last post by  gdmoody 
#1 ·
I have seen this term in a number of manuals, Headspace of a .45 ACP cartridge, which headspaces off the case mouth but have never understood what it meant.

Can someone explain it to me, in understandable terms, what it means and specifically its relevance to reloading .45ACP.

Thanks in advance.
 
#2 ·
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.
 
#4 ·
Just in case you didn't know, the head of the cartridge is the back end. The front, where the bullet is, is the mouth, while the back, where the markings are, is the head. That's why the markings are called "headstamps". :)

Many people refer to bullets as "heads", or "bullet heads". They are wrong.
 
#11 ·
There are NO STUPID questions but..... this is the reloading forum and it is assumed that people who come here care about reloading. Such people should read their reloading manuals. All the above info is in the reloading manuals introductory chapters. I urge all to read their manuals, and re-read them until they thoroughly understand at least the terms if not the process and the "why's" of those processes. The stickies above also are a good introduction if you at least understand some of the terms.

Those who come here to discuss commercial ammo (and that is just fine) might gain something by buying an reloading manual to get a better understanding of even commercially made ammo. I recommend the Hornady manual as it is very good at explaining the "how it works" of ammunition.

An informed reloader/shooter is at the first step of safety for reloading and shooting.

LDBennett
 
#80 ·
I know this is an old post, but this is some great advice. I do not reload. I buy commercial ammo. I love to read reloading manuals and all of you folk's posts on reloading. I've learned so much that I never would have.
Bravo LDBennet!
 
#12 ·
As always,good responses from Alpo and LD.Thanks guys for being such an asset to the forumn.Couldn't have done w/out ya'lls help.You have helped me,and i think i speak for others,many times.THANKS,Joe
 
#14 · (Edited)
Negative. They will headspace on the little lip, just fine. Howsomever, without the moon clip you have to either punch 'em out from the front with a pencil, or pick 'em out from the back with your thumbnail or pocketknife. The moon clip's real purpose is to let the ejector star push 'em out.

Very early Colt 1917s did not have the lip, and need the clips to work. Webleys don't have a lip, so if you have of them that has been shaved, it also requires clips. Smith, however, has had the lip from the beginning, and Colt went to it within about the first six months of production.
 
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#15 ·
or you could buy auto rim brass and have mini .45 colt cartridges that have a really thick rim (.090" compared to .060" of a normal revolver cartridge)
 
#16 · (Edited)
Negative. They will headspace on the little lip, just fine. Howsomever, without the moon clip you have to either punch 'em out from the front with a pencil, or pick 'em out from the back with your thumbnail or pocketknife. The moon clip's real purpose is to let the ejector star push 'em out.

Very early Colt 1917s did not have the lip, and need the clips to work. Webleys don't have a lip, so if you have of them that has been shaved, it also requires clips. Smith, however, has had the lip from the beginning, and Colt went to it within about the first six months of production.
So it is negative as far as headspacing .45 acp in a revolver without using a moon clip as long as you (1) like to pick them out with your fingernails or pocket knife, etc. and (2) you are not shooting any of the old .45 acp Colt model 1917 revolvers, made by the millions and used widely during WWI, that are not made with a headspace.

Thanks for the informative reply but I think I'll stick with my moon clips for now.
 
#17 ·
So it is negative as far as headspacing .45 acp in a revolver without using a moon clip as long as you (1) like to pick them out with your fingernails or pocket knife, etc. and (2) you are not shooting any of the old .45 acp Colt model 1917 revolvers, made by the millions and used widely during WWI, that are not made with a headspace.

Thanks for the informative reply but I think I'll stick with my moon clips for now.
They only made a little over 150 thousand, not "millions". They only did the "smooth-sided" chambers for about the first six months of production. Guns that had not been issued, when they changed over, were sent back to Colt to have new cylinders fitted.

BUT, your question was not "should you use the clips?", or "is it easier to shoot 'em while using the clips?", it was "Don't you have to moon the .45 acp to get it to headspace in a revolver?" So, I answered that question. NO, you don't HAVE TO.
 
#19 · (Edited)
like Tim I have read this in many places and as LD suggested this discussed to some degree in most reloading manuels..however...Alpo's explanation is so very concise that ther is almost no confusion inherent to it. i have always felt as if there was something i was missing in reading the reloading manuels..i now fell i really got the meaning!

THANKS ALPO!!!!
 
#21 ·
If the .45 acp is spaced on the mouth of the cartridge, then am I correct to think that crimping may allow the cartridge to slide too far foward without catching on the lip? I have been using a Lee factory crimp on my .45 acp, and I have not run into a problem. Now I am thouroughly confused, because what I just read tells me that I should be having a problem. What am I missing here?
 
#22 ·
If the .45 acp is spaced on the mouth of the cartridge, then am I correct to think that crimping may allow the cartridge to slide too far foward without catching on the lip? I have been using a Lee factory crimp on my .45 acp, and I have not run into a problem. Now I am thouroughly confused, because what I just read tells me that I should be having a problem. What am I missing here?
A taper crimp is not anything like a roll crimp, I always like to think of a taper crimp as a " squeeze " to get to the final dimension, it really just removes the flare from the seating process more than anything.
 
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#23 ·
Bluesea, it really depends on the gun.

I use the Lee Factory Crimp Die on my 45 ACPs. I have no problems with them in any of my 1911s. I can also shoot them without the moon clips in my 1917, 1937 and 625 Smith and Wesson revolvers. However, if I try to use them without the clips in my 1950 Smith and Wesson revolver, they fall past the step and will not fire. Firing them with the clips works, so I know the gun works. Using factory ammo without the clips works, so I know the step is there. But, my reloads will not work in THIS gun, without moon clips. The only thing I can come up with is that the chambers of THIS gun are at maximum size.
 
#25 ·
I had a fun experience in my local shop yesterday. A guy came in with three pieces of fired .223 brass. All three had the primers blown back just a bit, and one was split just about 1/4" in front of the head.
He said that these were the first three rounds he had fired in his brand new Marlin rifle. The guy behind the counter just kept saying that the only thing that could cause that would be overcharged ammo. I asked him if he had reloaded it, and he hadn't. It was factory ammo from two different manufacturers (Remington and Winchester).
I told him it was a headspace issue. Then the shop owner decided to call one of the guys he knew at Remington's service center in Illinois (shop owner used to be a sales rep for Remington). The phone call confirmed what I told him, and that rifle is going back to be rebarreled.
Before I mentioned headspace, the guys at the shop had just about convinced the guy to go home and try firing it with some Federal ammo. :rolleyes: While I've now read a couple different reloading manuals, it was this thread that originally taught me about headspace. So our discussions on here are helpful to the safety even of shooters who've never heard of TFF. :)
 
#26 ·
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
 
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