What is headspace?
- Thread starter promac
- Start date
- Location
- Hillbilly shack in the boonies
He's right, 
, or it could be the space between the bolt face and the chamber.
, or it could be the space between the bolt face and the chamber.
For most people the simplest way to view headspace will be to consider it the space between the boltface and the rear of the cartridge when the bolt is closed and the cartridge is as far forward in the chamber as it will go....
You don't want much space here... you want don't want any when you are making a reload.
To determine if the headspace of the chamber is correct steel gauges manufactured to an exact dimension are used.
You don't want much space here... you want don't want any when you are making a reload.
To determine if the headspace of the chamber is correct steel gauges manufactured to an exact dimension are used.
It translates to the space an ammo round has in the chamber. It can be seen as stated by Guntech, but in reality you need to imagine that the catridge will be seated against the bolt, so the space will actually be in the front of the cartridge.
-If the headspace is too tight (chamber is short), when the round is chambered it can push the bullet deaper into the cartridge or the cartridge can be compressed at the shoulder, this is not good cause it can create an increase in chamber pressure when fired.
-If the headspace is too loose (chamber is long); then excessive cartridge expansion can occur causing it to crack.
Each chamber (caliber) has an acceptable headspace range for safe performance. Generally one wants the fit between ammo and chamber to be the tightess (within spec) for accuracy and a looser fit for reliability (field use, allows for more variance in ammo sizes and crude that may be present).
-If the headspace is too tight (chamber is short), when the round is chambered it can push the bullet deaper into the cartridge or the cartridge can be compressed at the shoulder, this is not good cause it can create an increase in chamber pressure when fired.
-If the headspace is too loose (chamber is long); then excessive cartridge expansion can occur causing it to crack.
Each chamber (caliber) has an acceptable headspace range for safe performance. Generally one wants the fit between ammo and chamber to be the tightess (within spec) for accuracy and a looser fit for reliability (field use, allows for more variance in ammo sizes and crude that may be present).
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The steel gages are shaped like cartridges and are made to the spec required for a given chamber dimension. The steel gages will have one that should not fit (it's too long, just above max headspace spec), if it does fit this would indicate too much chamber headspace. The second gage is the minimum lenght of the headspace spec, and this one should fit, if it does not fit then that indicates your headspace is too short.
- Location
- Hillbilly shack in the boonies
All that was missing there is that the cartridge is taking up part of the space.
furet said:
As soon as the firing pin hits the primer, the case is driven forward until the shoulder stops it... (or the rim if it is a rimmed case)... as the pressure builds and the brass expands the case "sticks" to the walls of the chamber and if the pressure is high enough, it will stretch at the web of the case and the rear of the case will move rearward until it contacts the bolt face.
...so immediately when you fire, the "headspace" ends up at the back of the case.
Headspace is a firearms manufacturing tolerance. It allows the use of all manufacturer's ammo/brass in all like chambered firearms. It's a measurement between the bolt face and a spot on the chamber on the shoulder area for a rimless cartridge, the rim for a rimmed cartridge and the belt for a belted magnum. Straight walled cases, like the .30 carbine and rimless pistol cartridges, headspace on the case mouth. The cartridge itself does not have headspace. Only the firearm has headspace.
It has nothing to do with the length of the chamber. Bad headspace can be caused by a bolt that has stretched or compressed too.
Excessive headspace will cause pressure issues in the chamber. Really excessive headspace can cause the case to be driven back hard enough to break bolt lugs and send the bolt into your head. Insufficient headspace will cause hard chambering that can crush the case or not being able to chamber the round at all.
It has nothing to do with the length of the chamber. Bad headspace can be caused by a bolt that has stretched or compressed too.
Excessive headspace will cause pressure issues in the chamber. Really excessive headspace can cause the case to be driven back hard enough to break bolt lugs and send the bolt into your head. Insufficient headspace will cause hard chambering that can crush the case or not being able to chamber the round at all.
so theoretically you want as little headspace as possible, with out the bullet being tight? am i correct? Also a fired case that is reloaded and only neck sized should have the absolute minumum headspace for that particular gun, which I believe to be a very good thing, right?
I thought it was from the base of the case to the center of the shoulder, or on belted mags, the distance from the top of the belt to the case head. What is in your opinion, some of the better brass for reloading belted magnums.guntech said:
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If reloading a belted magnum, it is a good idea to adjust your sizing die so that headspace is controlled by the shoulder, not the belt; treat the case as if it were rimless. By doing this excessive fireforming of the case is eliminated, and case life and accuracy may benefit.
Bob Greenleaf designed the current version of the Savage 110 action. Brewer designed the original version. Bob experimented with excess headspace in a .30-06 110. With the barrel locknut system, it was easy to adjust the rifle with increasingly excessive headspace. All firing was done under controlled conditions, with factory ammunition. As long as the extractor held the cartridge against the boltface, the rifle fired and the case fireformed. He finally stopped when the rifle just wouldn't fire, because the primer could no longer be indented by the firing pin. The barrel had been unscrewed over one turn. There were no case failures, no gas escape, nothing. Cases would have been ruined for reloading, of course. The ammunition used was fresh commercial. If old, brittle, handloaded, etc. ammunition had been used, there could have been case separations.
IF a case were driven foreward by the firing pin, held foreward by pressure, and the case failed when the head was driven back to the boltface, gas could be released, which could be harmful depending on the design of the rifle. Excess headspace doesn't increase chamber pressure, but could result in release of gas. I am unaware of any lug failure being caused by increased backthrust on the bolt resulting from the casehead slapping back against the boltface.
Badly flattened primers can result from excess headspace, but are not indicative of excess pressure. The case is driven foreward, pressure builds, the front of the case is locked in place, the primer is driven back against the boltface, the case stretches, the casehead is driven back to the boltface, and the primer gets squashed in the process. If the primer is left standing proud, this suggests excess headspace coupled with insufficient pressure to stretch the case back to the bolface.
There are numerous rifles in regular use which would fail gauge tests. Lee Enfields are a case in point. It is not unusual to find .303 brass showing signs of incipient separation, even when fired in rifles which are still in service. This is why .303 brass should be very carefully inspected before being reloaded.
Bob Greenleaf designed the current version of the Savage 110 action. Brewer designed the original version. Bob experimented with excess headspace in a .30-06 110. With the barrel locknut system, it was easy to adjust the rifle with increasingly excessive headspace. All firing was done under controlled conditions, with factory ammunition. As long as the extractor held the cartridge against the boltface, the rifle fired and the case fireformed. He finally stopped when the rifle just wouldn't fire, because the primer could no longer be indented by the firing pin. The barrel had been unscrewed over one turn. There were no case failures, no gas escape, nothing. Cases would have been ruined for reloading, of course. The ammunition used was fresh commercial. If old, brittle, handloaded, etc. ammunition had been used, there could have been case separations.
IF a case were driven foreward by the firing pin, held foreward by pressure, and the case failed when the head was driven back to the boltface, gas could be released, which could be harmful depending on the design of the rifle. Excess headspace doesn't increase chamber pressure, but could result in release of gas. I am unaware of any lug failure being caused by increased backthrust on the bolt resulting from the casehead slapping back against the boltface.
Badly flattened primers can result from excess headspace, but are not indicative of excess pressure. The case is driven foreward, pressure builds, the front of the case is locked in place, the primer is driven back against the boltface, the case stretches, the casehead is driven back to the boltface, and the primer gets squashed in the process. If the primer is left standing proud, this suggests excess headspace coupled with insufficient pressure to stretch the case back to the bolface.
There are numerous rifles in regular use which would fail gauge tests. Lee Enfields are a case in point. It is not unusual to find .303 brass showing signs of incipient separation, even when fired in rifles which are still in service. This is why .303 brass should be very carefully inspected before being reloaded.
bcrdr said:
The datum line varies of different cases... for instance the datum line for measuring on .270 and 30-06 cases is where a 3/8 inch diameter would contact the shoulder... this measurement is only used by reamer makers and gauge makers... it is a useless specification to know for most of us. Rely on your tool maker to know what they are doing.
On belted magnums the measurement from the front of the belt to the rear of the case is supposed to be exactly .220". In fact it is usually is much less. Once magnum brass is fireformed you should laways make sure you don't opush the shoulder back on sizing. It is quite important for case life that you can feel the bolt close on sized brass...
I don't know what the best brass is for magnum cases.
I don't believe cases snap back and break locking lugs. If there is excessive headspace the case may rupture and excaping gases will do damage. I have never seen or heard of any locking lugs shear or break off on any commercial action.
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bruno said:
On reloads it is best if you can feel a stripped (no firing pin/ejector causing resistance) bolt close on a correctly sized case. What you are feeling is resistance caused by the fireformed case pushing against the boltface as you close the bolt... a perfect fit - no headspace. The bolt should not be hard to close, but you should be able to "feel it".
RhysFromNZ
New member
- Location
- New Zealand
and theres always rimmed case headspace... which is the thickness of the rim. qiute different to rimless case headspace.
