Relationship between headspace and chasing the lands?

[JFrank]

The chamber has headspace, case has setback to cycle freely through the chamber
Just to put it into perspective .003 is slightly more than a human hair and hardly enough to cause overworking.

Just my experience.

 

[searcher]

Just offering my experience on this
being that brass is soft compared to the action
I had it in mind to set the shoulder back perfectly to the chamber
IE: you could feel slight resistance closing the bolt on a newly sized piece of brass
------------------------
There were times where occasionally one piece of brass would be harder to close the bolt on than others
I decided while providing good consistency in what you spoke of
maybe that wasn't so good for the bolt lugs in the long run.
I prefer now to be easily able to close the bolt when chambering a piece of brass
so set the shoulder back somewhere in the area of .001" - .002"
(if it is .002" on a newly set up sizing die... I may decide to fool with it later)
any more than that and I would say its more for ensuring a hunting gun can cycle ammo if dirty

To get that "perfect" slight resistance when the bolt is down around 75% on a round-to-round basis is not easy without some pretty meticulous brass prep. Inconsistently annealed brass alone will result in a slight variation in resistance when closing the bolt due to brass spring-back. I strive to get all that as good as I can on my target rounds. For varmint work, I'm happy with .001"-.002" off the shoulder - and my A/R's .002" to .003". That small amount of resistance on the target loads doesn't concern me in regard to bolt wear. I just keep that bolt clean by pulling the bolt and wiping it every so often and lightly grease the lugs. Maybe one way to view the difference in bolt resistance is using it as a gauge of sorts to let you know how consistent your ammo is. With no resistance, there is no feedback in that respect.

 

[searcher]

IMO an absolutely horrible way to attempt to solve a doughnut situation.

I agree - to knock the shoulders back only .001" surely isn't buying anyone much room to avoid a doughnut - and that would be a rarity that the actual bullet being used would be able to be manipulated successfully with that .001". I was really "stretching" it as to why someone might bump the shoulder more than needed - and as to what their logic or purpose was. My point was more "why would you do this?" One could conceivably push the shoulder back on certain bullets and avoid a doughnut, provided no more than .004 - .005" were involved. That, of course, would result in a lot of brass stretch, premature case life - and a host of other issues with flattened primers, expanded bases, possible case ruptures after several firings.... As you say - a VERY bad way to avoid a doughnut.

 

[ELR LVR]

To get that "perfect" slight resistance when the bolt is down around 75% on a round-to-round basis is not easy without some pretty meticulous brass prep. Inconsistently annealed brass alone will result in a slight variation in resistance when closing the bolt due to brass spring-back. I strive to get all that as good as I can on my target rounds. For varmint work, I'm happy with .001"-.002" off the shoulder - and my A/R's .002" to .003". That small amount of resistance on the target loads doesn't concern me in regard to bolt wear. I just keep that bolt clean by pulling the bolt and wiping it every so often and lightly grease the lugs. Maybe one way to view the difference in bolt resistance is using it as a gauge of sorts to let you know how consistent your ammo is. With no resistance, there is no feedback in that respect.

Except if you ever get a sticky bolt, warm load etc
That easily wiped on grease on the lugs, is pretty much gone
And I don't carry grease tubes out in the field
------------------------------------------------------
I like my bolt to close easily especially in a repeater action, with magazine
smoothly cycling the bolt, providing follow up shots
Not every bolt gun is a single shot only bench gun

 

[M-61]

The chamber has headspace, case has setback to cycle freely through the chamber
Just to put it into perspective .003 is slightly more than a human hair and hardly enough to cause overworking.

Just my experience.

Nope. Just keep adding that .003 up.
Key word in your reply is “hardly”

 

[Wild Bill IV]

The posts from the experts comp shooters (gold and silver) are the very definition of personal customized re!oading!!! Each has a personal preference from zero (no headspace) to 0.003 bump (- 3 thou headspace) for bolt action rifles!!! Semiautomatic are different!!! I used 0.002 bump (FL form die) for my 3 early series Ruger 223 Mini-14s and never had a problem!!!! And they were quite accurate from rabbits and yotes on the run!!!! Or prairie dogs out to 250!!!!

But none of these members have brought up the physical aspects of repeat shooting!!! That aspect is thermal expansion!!!! The old experimental demonstration of the ball and ring!!! Heat the ring to expand and the ball will not pass through the ring!!! Cool the ball in an ice bath, or liquid nitrogen, and have a hot ring, the ball will slip through the ring!!!! THE VERY BASICS FOR THE PROPERTIES OF THERMAL EXPANSION AND CONTRACTION!!!

The chamber (the RING) and cartridges (the BALL) will have the same effect!!! The 1st couple of rounds will have slight bolt drop heaviness with zero bump!!!! After that, the chamber has swollen due to the thermal absorption with the bolt falling easier with each fast repeated shots!!! How does this affect the accuracy????

This is a question that our experts can answer that have done this type of testing!!!
I'm only experienced in the cool barrel shooting and would like know since I can no longer shoot a high power (fear of retinal detachment from Macular Regeneration in scope eye)!!!

I would prefer posts from truly tested experts!!!!!!

 

[ELR LVR]

The posts from the experts comp shooters (gold and silver) are the very definition of personal customized re!oading!!! Each has a personal preference from zero (no headspace) to 0.003 bump (- 3 thou headspace) for bolt action rifles!!! Semiautomatic are different!!! I used 0.002 bump (FL form die) for my 3 early series Ruger 223 Mini-14s and never had a problem!!!! And they were quite accurate from rabbits and yotes on the run!!!! Or prairie dogs out to 250!!!!

But none of these members have brought up the physical aspects of repeat shooting!!! That aspect is thermal expansion!!!! The old experimental demonstration of the ball and ring!!! Heat the ring to expand and the ball will not pass through the ring!!! Cool the ball in an ice bath, or liquid nitrogen, and have a hot ring, the ball will slip through the ring!!!! THE VERY BASICS FOR THE PROPERTIES OF THERMAL EXPANSION AND CONTRACTION!!!

The chamber (the RING) and cartridges (the BALL) will have the same effect!!! The 1st couple of rounds will have slight bolt drop heaviness with zero bump!!!! After that, the chamber has swollen due to the thermal absorption with the bolt falling easier with each fast repeated shots!!! How does this affect the accuracy????

This is a question that our experts can answer that have done this type of testing!!!
I'm only experienced in the cool barrel shooting and would like know since I can no longer shoot a high power (fear of retinal detachment from Macular Regeneration in scope eye)!!!

I would prefer posts from truly tested experts!!!!!!

I did perform such a test to see how the POWDER and LOAD would react when it heated up pretty much as hot as it would reallisticaly get in real world use.
More to test the vertical dispersion since it was for a long range rifle
I did not test for ease or resistance to bolt closure,
I know I did not have to fight bolt closure as the gun heated up.
I was pleased with how the load acted... showing only minimal vertical climbing on a
95 F day, 2 shots fired quickly to heat the chamber
the third successive round left to sit in the chamber
with the rifle cooking in the sun sun for 10 minutes after the second round was fired.
(Supposedly you dont want to let a round sit and heat up in the chamber if you expect it to go where the previous shot landed)
With this powder i felt confident I could leave a round chambered and wait for the window of opportunity to present itself without fumbling with jacking a round in, and then going to glass.

 

[JFrank]

As long as you see a reason to work the brass. .003 + headspace back and forth.

That actually happened to me about ten years ago from listening to all the horse shit on the internet.

But no one with any experience would do that.

 

[searcher]

Except if you ever get a sticky bolt, warm load etc
That easily wiped on grease on the lugs, is pretty much gone
And I don't carry grease tubes out in the field
------------------------------------------------------
I like my bolt to close easily especially in a repeater action, with magazine
smoothly cycling the bolt, providing follow up shots
Not every bolt gun is a single shot only bench gun

What you say has a lot of merit. And, as I had said in the post prior to the one you noted, I also use different setbacks for various uses. In the statement I made that you addressed, my thoughts were meant more for target shooting. I assumed when speaking of only .001" movement of anything - the poster was involved in target shooting. In my big game hunting rifles, I don't worry about wanting to have bolt resistance on the close. I don't need the additional potential accuracy it might give, nor any extra brass life it might provide. Most of a batch is lost in the field over the course of hunts before I'd get to load it enough times to end a "natural" life. Regardless - I still keep the shoulder quite close.

 

[Wild Bill IV]

I did perform such a test to see how the POWDER and LOAD would react when it heated up pretty much as hot as it would reallisticaly get in real world use.
More to test the vertical dispersion since it was for a long range rifle
I did not test for ease or resistance to bolt closure,
I know I did not have to fight bolt closure as the gun heated up.
I was pleased with how the load acted... showing only minimal vertical climbing on a
95 F day, 2 shots fired quickly to heat the chamber
the third successive round left to sit in the chamber
with the rifle cooking in the sun sun for 10 minutes after the second round was fired.
(Supposedly you dont want to let a round sit and heat up in the chamber if you expect it to go where the previous shot landed)
With this powder i felt confident I could leave a round chambered and wait for the window of opportunity to present itself without fumbling with jacking a round in, and then going to glass.

Nice!!!
However, I had a hot hunting load (temperature sensitive IMR 4064) that I avoided shooting above 80° since deer season hardly gets that hot!!!
It was slightly above max Sierra Data!!!
I shot at a yote at 800 yards in tall grass in a low lying area on a really warm, early December day!!
I loaded another round in the chamber, set the safety, and waited!!!!
Nothing moved for about 15 minutes!!!
Me and two other brothers went into the bottom looking for that coyote!!!
No dead coyote!!!
Set the guns down with bipod legs out in a sandy clearing in the sun with no wind in the bottom!!!
Looked through the grass for blood for about half an hour!!!
Found no blood, but a shining sun reflection from the old dump on a hill about 1000 caught our eyes!!!
There we lots of 1 gallon, empty glass jars in that makes old illegal dump!!!
Got behind the rifle, adjusted for range, slight wind above the bottom, and target elevation (up hill shot)!!
I DIDN'T EVEN THINK ABOUT THAT RIFLE SETTING IN THE HOT SUN WITH NO AIR MOVEMENT COOKING THE CARTRIDGE IN ITS CHAMBER!!!!!!!!!!!!!!!!
Slowly squeezed the trigger, and then, ALL HE!! broke lose!!!!!
Extremely hard recoil followed by a dense blueish/dark grey gas plume spiralling out of the relieve port!!!
The fumes from that plume burnt the sinus and took my breathe away!!!
Three hard palm smacks to open the bolt!!!
The case ejected and I heard a slight clinging sound of something falling in the action!!!
The fired case had no primer and the primer pocket had considerable growth!!
The prime fell into the action!!!
The primer was pierced, and split on the cup after shaking it out of the action!!!!

BUT, THE SHINY GLARE WAS GONE!!!!

A LESSON LEARNED FROM THE SCHOOL OF HARD KNOCKS!!!!!!
No pierced primers since that day!!!!!!!

 

[searcher]

I did perform such a test to see how the POWDER and LOAD would react when it heated up pretty much as hot as it would reallisticaly get in real world use.
More to test the vertical dispersion since it was for a long range rifle
I did not test for ease or resistance to bolt closure,
I know I did not have to fight bolt closure as the gun heated up.
I was pleased with how the load acted... showing only minimal vertical climbing on a
95 F day, 2 shots fired quickly to heat the chamber
the third successive round left to sit in the chamber
with the rifle cooking in the sun sun for 10 minutes after the second round was fired.
(Supposedly you dont want to let a round sit and heat up in the chamber if you expect it to go where the previous shot landed)
With this powder i felt confident I could leave a round chambered and wait for the window of opportunity to present itself without fumbling with jacking a round in, and then going to glass.

If you had expanded that test to say, fire a quick string of ten or more rounds - then let one sit in the chamber - your results would surely have been a bit more pronounced. Of course, the diameter and length of the barrel will dictate how quickly it heats up too. I used to shoot long strings over a chrono (not for this purpose), but it taught me a valuable lesson early on to never slide another round into that hot chamber when shooting until I was ready to shoot where the chamber is always hot - especially if using a warm load. I also learned that to truly test a good varmint load that will be used when the barrel is really hot - one must test the load when the barrel is really hot too. I've had "great" loads worked up that fell apart after the barrel had about 30-40 rounds fired within 5 or 6 minutes on a hot squirrel field. I initially thought it was barrel stress, though changing/altering the load often cured the problem. Even when bench rest shooting, if conditions changed in the middle of a string, I'd not want a round in the chamber until I was ready to resume. Just paranoid? Maybe a little.

 

[Wild Bill IV]

If you had expanded that test to say, fire a quick string of ten or more rounds - then let one sit in the chamber - your results would surely have been a bit more pronounced. Of course, the diameter and length of the barrel will dictate how quickly it heats up too. I used to shoot long strings over a chrono (not for this purpose), but it taught me a valuable lesson early on to never slide another round into that hot chamber when shooting until I was ready to shoot where the chamber is always hot - especially if using a warm load. I also learned that to truly test a good varmint load that will be used when the barrel is really hot - one must test the load when the barrel is really hot too. I've had "great" loads worked up that fell apart after the barrel had about 30-40 rounds fired within 5 or 6 minutes on a hot squirrel field. I initially thought it was barrel stress, though changing/altering the load often cured the problem. Even when bench rest shooting, if conditions changed in the middle of a string, I'd not want a round in the chamber until I was ready to resume. Just paranoid? Maybe a little.

Those rounds will start COOKING!!!!

My dad taught field artillery while in the NG as an officer!!!!

A gunner/trainer officer came down with a bug (probably a hangover being away from the wife an all in a different state) and the NG camp commander asked dad (an expert marksman) to fill in since Dad's big gun squads (155mm) where training on field maintenance exercise!! His fill in duty was training with the a Quad 50 mounted on a duce!!!!
The green horn college kid had never fired a quad!!! Dad gave him quick instructions on the operation of the Quad and barrel cycling with short bursts!!! He grabbed the handles and started firing, locked up on the triggers with his thumbs frozen under the high/low barrel selectors, freaking out and started swinging the barrels away from the down range targets!!! Dad had to knock him off the gun and tackled him to the bed of the duce!!! A couple of Guardsmen jumped up and over the side away from the barrels and aided in restraining him!!! He ordered one of the Guardsmen to clear the weapon of the cooking rounds in the chambers!!! Meanwhile, an old timer on brass clean up detail, took his helmet off, in discuss, and was climbing up on the wrong side of the duce (down range/barrel muzzle side) before the "All Clear" command to use the helmet to scoop up the spent brass!!

One round COOKED OFF, leaving a 1/2" hole in the helmet just before the Guardsmen could clear the 2 HOT upper chambers and unfired lowers and give the "All Clear" command!

The base commander put the kid on a bus back home, had the old timer wear that helmet with hole till his two week duty was up, gave him a new lid and hung the helmet with hole on the Quad 50!!! This was after the Military Observer's Report to the General!!!

Dad's finally military duty as an Army Reserve Officer (Lt. Col.) was teaching Military tactics at Leavenworth Officers School (Later named Leavenworth War College).

 

[searcher]

Those rounds will start COOKING!!!!

My dad taught field artillery while in the NG as an officer!!!!

A gunner/trainer officer came down with a bug (probably a hangover being away from the wife an all in a different state) and the NG camp commander asked dad (an expert marksman) to fill in since Dad's big gun squads (155mm) where training on field maintenance exercise!! His fill in duty was training with the a Quad 50 mounted on a duce!!!!
The green horn college kid had never fired a quad!!! Dad gave him quick instructions on the operation of the Quad and barrel cycling with short bursts!!! He grabbed the handles and started firing, locked up on the triggers with his thumbs frozen under the high/low barrel selectors, freaking out and started swinging the barrels away from the down range targets!!! Dad had to knock him off the gun and tackled him to the bed of the duce!!! A couple of Guardsmen jumped up and over the side away from the barrels and aided in restraining him!!! He ordered one of the Guardsmen to clear the weapon of the cooking rounds in the chambers!!! Meanwhile, an old timer on brass clean up detail, took his helmet off, in discuss, and was climbing up on the wrong side of the duce (down range/barrel muzzle side) before the "All Clear" command to use the helmet to scoop up the spent brass!!

One round COOKED OFF, leaving a 1/2" hole in the helmet just before the Guardsmen could clear the 2 HOT upper chambers and unfired lowers and give the "All Clear" command!

The base commander put the kid on a bus back home, had the old timer wear that helmet with hole till his two week duty was up, gave him a new lid and hung the helmet with hole on the Quad 50!!! This was after the Military Observer's Report to the General!!!

Dad's finally military duty as an Army Reserve Officer (Lt. Col.) was teaching Military tactics at Leavenworth Officers School (Later named Leavenworth War College).

Yep - I was on an 81 MM mortar crew in the Marines and when "firing for effect", we'd get those tubes way too hot to touch. I recall a "dud" and the protocol was to wait a specified period of time, then one guy would tip the tube and another guy would take the round and carry it away from the perimeter of the mortar pits while everyone else stayed clear. Not my favorite job. One would never know if it did go off.