Explaining Headspace - The Firearms Forum

Insulation Tim · 06-06-2010, 08:39 AM

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.

Alpo · 06-06-2010, 09:32 AM

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.

cycloneman · 06-06-2010, 09:34 AM

EXPLAINING HEADSPACE? THAT IS THE EMPTY SPACE IN OBAMA'S HEAD.

Alpo · 06-06-2010, 09:35 AM

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.

muddober · 06-06-2010, 09:54 AM

Alpo, I must admit you did a great job of explaining headspace but you must admit cycloneman also did a great job of simplifying it.

Ron

Insulation Tim · 06-06-2010, 11:51 AM

Alpo...thank you very much. I also never knew that the cartridge end with the primer is the "head". Even at 63, I learn something new everyday....or at least try to.

Terry_P · 06-06-2010, 04:30 PM

So it isn't where you put the toilet?

Alpo:

Thanks as I wasn't real sure either but have a good understanding now.

Alpo · 06-06-2010, 06:41 PM

Y'all are quite welcome. Glad I could help.

JLA · 06-06-2010, 08:18 PM

alpo is a most useful asset to the forum

JohnTheCalifornian · 06-06-2010, 11:19 PM

Should be thrown up top for a sticky. Good info for people to know.

LDBennett · 06-07-2010, 06:44 AM

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

accident · 06-09-2010, 12:47 PM

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

DGG! · 06-09-2010, 04:31 PM

Don't you have to moon the .45 acp to get it to headspace in a revolver?

Alpo · 06-09-2010, 04:57 PM

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.

JLA · 06-09-2010, 08:21 PM

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)

DGG! · 06-10-2010, 09:58 AM

Quote:

Originally Posted by Alpo

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.

Alpo · 06-10-2010, 10:40 AM

Quote:

Originally Posted by DGG!

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.

upsguy · 02-10-2011, 02:38 PM

Ive been checking out past threads and found this one very useful. Im really glad I found this forum. You guys ROCK!!!
BTW, this thread SHOULD be a sticky...

hunter29180 · 02-10-2011, 06:09 PM

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!!!!

LesterPTelestrat · 02-13-2011, 09:41 PM

Diddo that hunter29189. I'm meticulous about case length when loading .45 ACP so have never had an issue. I just didn't really understand why it was so important until now. Very good thread!

bluesea112 · 08-15-2011, 09:49 PM

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?

woolleyworm · 08-15-2011, 09:52 PM

Quote:

Originally Posted by bluesea112

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.

Alpo · 08-15-2011, 10:38 PM

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.

bluesea112 · 08-15-2011, 11:32 PM

Thanks for clearing that up guys. I forgot to mention that I am shooting the .45 acp's in a Sig P220.

CampingJosh · 09-03-2011, 11:35 AM

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.

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.

06-06-2010, 08:39 AM	#1
Insulation Tim Advanced Senior Member Join Date: Oct 2008 Location: Ohio Contributor Posts: 2,298	Explaining Headspace 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. __________________ Tim *"Remember the Ark was built by amateurs....Professionals built the Titanic"* -->

06-06-2010, 09:32 AM	#2
Alpo Advanced Senior Member Join Date: Feb 2007 Location: NW Florida Posts: 8,662	Re: Explaining Headspace 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. __________________ Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297 I always take precautions. Beware the Evil Bullet Fairies.

06-06-2010, 09:34 AM	#3
cycloneman Advanced Senior Member Join Date: Dec 2008 Location: Louisiana Posts: 7,404	Re: Explaining Headspace EXPLAINING HEADSPACE? THAT IS THE EMPTY SPACE IN OBAMA'S HEAD. __________________ Who are you going to serve today?

06-06-2010, 09:35 AM	#4
Alpo Advanced Senior Member Join Date: Feb 2007 Location: NW Florida Posts: 8,662	Re: Explaining Headspace 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. __________________ Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297 I always take precautions. Beware the Evil Bullet Fairies.

06-06-2010, 09:54 AM	#5
muddober Advanced Senior Member Join Date: Sep 2008 Posts: 1,436	Re: Explaining Headspace Alpo, I must admit you did a great job of explaining headspace but you must admit cycloneman also did a great job of simplifying it. Ron

06-06-2010, 11:51 AM	#6
Insulation Tim Advanced Senior Member Join Date: Oct 2008 Location: Ohio Contributor Posts: 2,298	Re: Explaining Headspace Alpo...thank you very much. I also never knew that the cartridge end with the primer is the "head". Even at 63, I learn something new everyday....or at least try to. __________________ Tim *"Remember the Ark was built by amateurs....Professionals built the Titanic"*

06-06-2010, 04:30 PM	#7
Terry_P Advanced Senior Member Join Date: Mar 2008 Location: NH Posts: 2,513	Re: Explaining Headspace So it isn't where you put the toilet? Alpo: Thanks as I wasn't real sure either but have a good understanding now. __________________ NRA and NAHC Life "Both oligarch and tyrant mistrust the people, and therefore deprive them of their arms." -Aristotle

06-06-2010, 06:41 PM	#8
Alpo Advanced Senior Member Join Date: Feb 2007 Location: NW Florida Posts: 8,662	Re: Explaining Headspace Y'all are quite welcome. Glad I could help. __________________ Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297 I always take precautions. Beware the Evil Bullet Fairies.

06-06-2010, 08:18 PM	#9
JLA TFF Moderator/Host Join Date: Feb 2007 Location: Heart Of Texas Contributor Posts: 17,317	Re: Explaining Headspace alpo is a most useful asset to the forum __________________ It takes 43 muscles to frown, 17 to smile, and 3 for proper trigger squeeze. The latest caliber or gear is no substitute for experience and skill. Rifles and cartridges don't make hits -- shooters do. Fact of life: After Monday and Tuesday, even the calendar says WTF!

06-06-2010, 11:19 PM	#10
JohnTheCalifornian V.I.P. Member Join Date: Jun 2009 Location: Bakersfield Posts: 432	Re: Explaining Headspace Should be thrown up top for a sticky. Good info for people to know. __________________ Im not a complete idiot.... parts are missing

06-07-2010, 06:44 AM	#11
LDBennett Advanced Senior Member Join Date: Dec 2003 Location: Hesperia, CA Posts: 5,715	Re: Explaining Headspace 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

06-09-2010, 12:47 PM	#12
accident V.I.P. Member Join Date: Sep 2009 Location: middle GA Posts: 364	Re: Explaining Headspace 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 __________________ "The strongest reason for the people to retain the Right to keep and bear arms is, as a last resort, to protect themselves against tyranny in Government." Thomas Jefferson

06-09-2010, 04:31 PM	#13
DGG! V.I.P. Member Join Date: Apr 2010 Posts: 160	Re: Explaining Headspace Don't you have to moon the .45 acp to get it to headspace in a revolver?

06-09-2010, 04:57 PM	#14
Alpo Advanced Senior Member Join Date: Feb 2007 Location: NW Florida Posts: 8,662	Re: Explaining Headspace 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. __________________ Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297 I always take precautions. Beware the Evil Bullet Fairies. Last edited by Alpo; 06-09-2010 at 04:58 PM..

06-09-2010, 08:21 PM	#15
JLA TFF Moderator/Host Join Date: Feb 2007 Location: Heart Of Texas Contributor Posts: 17,317	Re: Explaining Headspace 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) __________________ It takes 43 muscles to frown, 17 to smile, and 3 for proper trigger squeeze. The latest caliber or gear is no substitute for experience and skill. Rifles and cartridges don't make hits -- shooters do. Fact of life: After Monday and Tuesday, even the calendar says WTF!

02-10-2011, 02:38 PM	#18
upsguy V.I.P. Member Join Date: Jan 2011 Location: CROOK Co. Illinois Posts: 77	Re: Explaining Headspace Ive been checking out past threads and found this one very useful. Im really glad I found this forum. You guys ROCK!!! BTW, this thread SHOULD be a sticky... __________________ Your best weapon is your brain, don't leave home without it.

02-10-2011, 06:09 PM	#19
hunter29180 Advanced Senior Member Join Date: Jan 2011 Location: in a motorhome where ever we park! Contributor Posts: 1,627	Re: Explaining Headspace 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!!!! Last edited by hunter29180; 02-10-2011 at 06:09 PM.. Reason: spelling again! wife is ultimate spellcheck...

02-13-2011, 09:41 PM	#20
LesterPTelestrat V.I.P. Member Join Date: Aug 2010 Posts: 65	Re: Explaining Headspace Diddo that hunter29189. I'm meticulous about case length when loading .45 ACP so have never had an issue. I just didn't really understand why it was so important until now. Very good thread! Last edited by LesterPTelestrat; 02-13-2011 at 09:42 PM..

08-15-2011, 09:49 PM	#21
bluesea112 Advanced Senior Member Join Date: Nov 2005 Location: West, TX Contributor Posts: 1,257	Re: Explaining Headspace 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?

08-15-2011, 10:38 PM	#23
Alpo Advanced Senior Member Join Date: Feb 2007 Location: NW Florida Posts: 8,662	Re: Explaining Headspace 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. __________________ Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297 I always take precautions. Beware the Evil Bullet Fairies.

08-15-2011, 11:32 PM	#24
bluesea112 Advanced Senior Member Join Date: Nov 2005 Location: West, TX Contributor Posts: 1,257	Re: Explaining Headspace Thanks for clearing that up guys. I forgot to mention that I am shooting the .45 acp's in a Sig P220.

09-03-2011, 11:35 AM	#25
CampingJosh TFF Moderator/Host Join Date: Sep 2007 Location: Indiana Contributor Posts: 4,788	Re: Explaining Headspace 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. 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. __________________ Nothing posted on TheFirearmsForum.com constitutes legal, accounting, gunsmithing, or other professional advice. Readers are encouraged to consult with qualified professionals for real advice. Your life is lived at your own risk. Don't blame me for the dumb things you do.