Relationship between headspace and chasing the lands?

[TommyD11730]

Hey guys, hope you all got some shooting in this weekend. For me, it was a rainout.
So Im sitting at the reloading bench today. I thought I would try bumping the headspace just a touch on my current load. So, let's just say my headspace comparitor measures my case at 1.530". I decided Im going to push them back to 1.5285". By shortening my base to shoulder what does it do to my bullet to lands? Does it move fwd 1.5 tho? Backwards? No change?

Thanks guys Im trying to wrap my head around this relationship.

 

[WillyTP]

No change in relation to lands. It does decrease the amount of bullet base depth into the neck by .0015”. So less bullet to neck contact area.

 

[Straightshooter1]

Hey guys, hope you all got some shooting in this weekend. For me, it was a rainout.
So Im sitting at the reloading bench today. I thought I would try bumping the headspace just a touch on my current load. So, let's just say my headspace comparitor measures my case at 1.530". I decided Im going to push them back to 1.5285". By shortening my base to shoulder what does it do to my bullet to lands? Does it move fwd 1.5 tho? Backwards? No change?

Thanks guys Im trying to wrap my head around this relationship.

Your distance to the lands will remain the same, since it's your seating pin in the seating die that determine where the bullet is regardless of where your headspace.

What changing the headspace does do is change the case volume and the trim length of the case.

 

[Evan]

Depends how you seat your bullets. I have disks under my round in wilson inline seaters so the seater rides on the shoulder and doesn’t sit on the arbor press at all to provide a consistent bullet to shoulder distance. If you seat more traditionally, then the bullet to base of case is the controlled dimension and your shoulder to base, or headspace, becomes important to control.

 

[dellet]

Bullet jump or jam is directly related to the shoulder. In a rimless, shouldered cartridge.
A bullet set at touch, with zero headspace, will still be at touch if you bump back the shoulder .0015”, but you will have .0015” of space between shoulder and the chamber. Technically you will be headspacing off the bullet, the contact points will be the case head and the bullet instead of case head and shoulder. This is how you fire form short shouldered brass.

Moving the shoulder back, more headspace, allows the bullet to be closer to the lands, a longer distance from shoulder to bullet ogive. It also lengthens the neck, so the same overall case length, is also .0015” closer to the end of the chamber.

 

[searcher]

I was wondering why one might want to push the shoulder back any further than light contact, though perhaps using it as a trick to get out of the doughnut with a certain bullet is conceivable. The tradeoff being, of course, more case stretch. I may be the odd man out on this one, but I don't necessarily buy into the bullet remaining unaffected in relation to the bore when the shoulder is moved back, while the bullet is seated the same. The slop introduced between shoulder and chamber provides additional forward and rearward slop of the entire cartridge, bullet included, unless the bullet is jammed. That translates to minute differences in muzzle exit timing? In the end, the target says what is working best - but....

 

[Straightshooter1]

I was wondering why one might want to push the shoulder back any further than light contact, though perhaps using it as a trick to get out of the doughnut with a certain bullet is conceivable. The tradeoff being, of course, more case stretch. I may be the odd man out on this one, but I don't necessarily buy into the bullet remaining unaffected in relation to the bore when the shoulder is moved back, while the bullet is seated the same. The slop introduced between shoulder and chamber provides additional forward and rearward slop of the entire cartridge, bullet included, unless the bullet is jammed. That translates to minute differences in muzzle exit timing? In the end, the target says what is working best - but....

Ideally, yes . . . having the shoulder have light contact is good and not only helps with consistency by also helps with case life. But, there's other issues that need to keep in mind. . . like with a hunting rifle, dirt and grim and make it way into the chamber where getting a round fed from a mag could result in not being able to chamber the round, huh?

When a cartridge is chambered, isn't the ejector pin, like in most bolts, pushing the case forward to touch. . . assuming the case as been fire formed and shoulder only bumped a couple thousandths?

 

[searcher]

Ideally, yes . . . having the shoulder have light contact is good and not only helps with consistency by also helps with case life. But, there's other issues that need to keep in mind. . . like with a hunting rifle, dirt and grim and make it way into the chamber where getting a round fed from a mag could result in not being able to chamber the round, huh?

When a cartridge is chambered, isn't the ejector pin, like in most bolts, pushing the chase forward to touch. . . assuming the case as been fire formed and shoulder only bumped a couple thousandths?

I assumed this shooter is target shooting regarding the tight case contact. I see the point about dirt and grime, but personally, I'd rather know there IS dirt or grime in my chamber. Slop will hide it and allow the round to fire with such dirt and grim in the chamber to a point? Two ways to look at it, I guess. Regarding the ejector pin pushing the cartridge forward, that is true to a degree, but the case gets pushed rearward before bullet exits when firing, so the bullet ends up further from the bore than one thinks - if seating to the same depth and pushing the shoulder back. Whether his pushing the shoulder back is good or bad depends on why he wants to do it, I suppose. For accuracy and case life - best to keep them tighter to the chamber as a rule. The difference in case life by pushing back .001" is very little - but that .001 deviation for the bullet at the lands could affect accuracy meaningfully, I think. Otherwise, we could be happy with .001" difference in seated bullet depth. And maybe some are O.K. with that too.

 

[Wild Bill IV]

Ideally, yes . . . having the shoulder have light contact is good and not only helps with consistency by also helps with case life. But, there's other issues that need to keep in mind. . . like with a hunting rifle, dirt and grim and make it way into the chamber where getting a round fed from a mag could result in not being able to chamber the round, huh?

When a cartridge is chambered, isn't the ejector pin, like in most bolts, pushing the chase forward to touch. . . assuming the case as been fire formed and shoulder only bumped a couple thousandths?

In most instances, yes the extractor pushes the cartridge in for nice chamber to cartridge geometry (case shoulder to chamber shoulder taper self centering)!! However, the case is lying in the bottom of the chamber as it moves forward!!! The extractor can, and will in a few instances, cause offset loading or force (since the extractor is located off center), and with enough bump and no bullet jam, can cause a slightly non concentric lock in from a chamber to shoulder hangup!!!! After 40 Years of drafting (35 years of CADD starting with the very crude MathCADD and Autodesk AutoCADD version 4 on the old 720KB floppies) of tooling and machine design, hang ups can occur!!! Especially with shoulder angles >30°!!!! The Morse Taper is a self locking, self centering, tool holder in itself with that really low incidental angle or taper!!!

I'm an old timer, long range hunter, that has used 0.000" bump most of my life with cartridges </= 30° with outstanding tight groups in the target (<0.1 to ~0.2 MOA with old high end factory hunting/target rifles)!!! I have experienced a few hang ups with the 6.5PRC and 280AI (shoulder angles >30°)!! The rifle exposes this defect in concentrics when checking each resized case in the rifles chamber during bolt locking!!! In the shooting sports, feel is important, even in the bolt drop and lift!!! The rifle feel is just as important as the target!!! When bolt drop increases, the case is not concentric to the chamber, or its time to anneal when minimal bump can not be achieved with verification using the bump comparitor!!!! With zero bump, there is slightly more resistances in final bolt drop than just extractor spring loading!!!!!!!!

My hunting loads are 0 bump sizing!!! IMHO (and tooling/machine design experiences), Zero bump eliminates minute brass movement in the stretch region in the case lower body, eliminates bolt hammering, reduces locking lug cam flattening, and vastly improves the lock in geometry!!! Headspace can change, very slightly, from continuous lose locking lug engagement and bolt slamming!!!! However, if I was shooting target competition, I would experiment with minimal (0.0005" to 0.0010") bump!!! The rifle, and the target will let you know if you have achieved the minimum bump required for your type of shooting!!!

I still use the old Bonanza COAX press with the high end Bonanza, Forster, and Redding dies!!! I have never had a FL die make contact with the jaws in minimal bump at full cam over!!! Plus, the floating die, moving jaws create concentric reloads where the sizing dies come to case, not the case to the dies in rigid die setting/ram presses!!!!

 

[mgunderson]

I typically jump bullets in my match rifles. Pushing the shoulder back 1.5 thousands may require you push the bullets back the same distance. Depends which side of the seating depth node you like to sit on. Best to let the rifle tell you what it wants. My arbor press and dies travel to the range with me when I make changes like this. It is easy to push the back 2 thou if needed.

 

[Straightshooter1]

I assumed this shooter is target shooting regarding the tight case contact. I see the point about dirt and grime, but personally, I'd rather know there IS dirt or grime in my chamber. Slop will hide it and allow the round to fire with such dirt and grim in the chamber to a point? Two ways to look at it, I guess. Regarding the ejector pin pushing the cartridge forward, that is true to a degree, but the case gets pushed rearward before bullet exits when firing, so the bullet ends up further from the bore than one thinks - if seating to the same depth and pushing the shoulder back. Whether his pushing the shoulder back is good or bad depends on why he wants to do it, I suppose. For accuracy and case life - best to keep them tighter to the chamber as a rule. The difference in case life by pushing back .001" is very little - but that .001 deviation for the bullet at the lands could affect it meaningfully, I think. Otherwise, we could be happy with .001" difference in seated bullet depth. And maybe some are O.K. with that too.

In most instances, yes the extractor pushes the cartridge in for nice chamber to cartridge geometry (case shoulder to chamber shoulder taper self centering)!! However, the case is lying in the bottom of the chamber as it moves forward!!! The extractor can, and will in a few instances, cause offset loading or force (since the extractor is located off center), and with enough bump and no bullet jam, can cause a slightly non concentric lock in from a chamber to shoulder hangup!!!! After 40 Years of drafting (35 years of CADD starting with the very crude MathCADD and Autodesk AutoCADD version 4 on the old 720KB floppies) of tooling and machine design, hang ups can occur!!! Especially with shoulder angles >30°!!!! The Morse Taper is a self locking, self centering, tool holder in itself with that really low incidental angle or taper!!!

I'm an old timer, long range hunter, that has used 0.000" bump most of my life with cartridges </= 30° with outstanding tight groups in the target (<0.1 to ~0.2 MOA with old high end factory hunting/target rifles)!!! I have experienced a few hang ups with the 6.5PRC and 280AI (shoulder angles >30°)!! The rifle exposes this defect in concentrics when checking each resized case in the rifles chamber during bolt locking!!! In the shooting sports, feel is important, even in the bolt drop and lift!!! The rifle feel is just as important as the target!!! When bolt drop increases, the case is not concentric to the chamber, or its time to anneal when minimal bump can not be achieved with verification using the bump comparitor!!!! With zero bump, there is slightly more resistances in final bolt drop than just extractor spring loading!!!!!!!!

My hunting loads are 0 bump sizing!!! IMHO (and tooling/machine design experiences), Zero bump eliminates minute brass movement in the stretch region in the case lower body, eliminates bolt hammering, reduces locking lug cam flattening, and vastly improves the lock in geometry!!! Headspace can change, very slightly, from continuous lose locking lug engagement and bolt slamming!!!! However, if I was shooting target competition, I would experiment with minimal (0.0005" to 0.0010") bump!!! The rifle, and the target will let you know if you have achieved the minimum bump required for your type of shooting!!!

I still use the old Bonanza COAX press with the high end Bonanza, Forster, and Redding dies!!! I have never had a FL die make contact with the jaws in minimal bump at full cam over!!! Plus, the floating die, moving jaws create concentric reloads where the sizing dies come to case, not the case to the dies in rigid die setting/ram presses!!!!

I've been bumping ~.001 for a long time now and noted it's been a benefit in my shooting as well as it appears to have been contributing in giving me extended case life. I've even done some .000 bump, but wasn't sure what benefit I might be getting.

I don't have the old Bonanza, but I really do like my Forster Co-Ax!!!!!! For the hell of it, I got hold of a Nexus and while it does a pretty good job similar for concentricity, the Co-Ax is still, what I'd call, a better press. Love the moving jaws vs having to change out case holders!!!!!

 

[JFrank]

This may be unpopular but imho a zero set back might not be the best way to keep a rifle cycling after ignition, nothing good comes from fighting a bolt open during a relay or hunting when you need to send another round.
Additionally, .002 -.0025 is only the thickness of a human hair, that I can’t imagine being considered excess movement on brass causing shorten life span. I dont recall ever wearing out brass unless it’s primer pockets getting loose.

 

[D-4297]

In most instances, yes the extractor pushes the cartridge in for nice chamber to cartridge geometry (case shoulder to chamber shoulder taper self centering)!! However, the case is lying in the bottom of the chamber as it moves forward!!! The extractor can, and will in a few instances, cause offset loading or force (since the extractor is located off center), and with enough bump and no bullet jam, can cause a slightly non concentric lock in from a chamber to shoulder hangup!!!! After 40 Years of drafting (35 years of CADD starting with the very crude MathCADD and Autodesk AutoCADD version 4 on the old 720KB floppies) of tooling and machine design, hang ups can occur!!! Especially with shoulder angles >30°!!!! The Morse Taper is a self locking, self centering, tool holder in itself with that really low incidental angle or taper!!!

I'm an old timer, long range hunter, that has used 0.000" bump most of my life with cartridges </= 30° with outstanding tight groups in the target (<0.1 to ~0.2 MOA with old high end factory hunting/target rifles)!!! I have experienced a few hang ups with the 6.5PRC and 280AI (shoulder angles >30°)!! The rifle exposes this defect in concentrics when checking each resized case in the rifles chamber during bolt locking!!! In the shooting sports, feel is important, even in the bolt drop and lift!!! The rifle feel is just as important as the target!!! When bolt drop increases, the case is not concentric to the chamber, or its time to anneal when minimal bump can not be achieved with verification using the bump comparitor!!!! With zero bump, there is slightly more resistances in final bolt drop than just extractor spring loading!!!!!!!!

My hunting loads are 0 bump sizing!!! IMHO (and tooling/machine design experiences), Zero bump eliminates minute brass movement in the stretch region in the case lower body, eliminates bolt hammering, reduces locking lug cam flattening, and vastly improves the lock in geometry!!! Headspace can change, very slightly, from continuous lose locking lug engagement and bolt slamming!!!! However, if I was shooting target competition, I would experiment with minimal (0.0005" to 0.0010") bump!!! The rifle, and the target will let you know if you have achieved the minimum bump required for your type of shooting!!!

I still use the old Bonanza COAX press with the high end Bonanza, Forster, and Redding dies!!! I have never had a FL die make contact with the jaws in minimal bump at full cam over!!! Plus, the floating die, moving jaws create concentric reloads where the sizing dies come to case, not the case to the dies in rigid die setting/ram presses!!!!

I fully agree with much of what is stated here . Also a retired Tool & Die-maker , with a Mech Engineering Degree , ( Don't hold it against me ) and the closer and tighter the brass fits to your chamber , the more consistent and accurate your round will be . Case slop is NOT your friend ! I only bump .001 and consistently shoot 197 and better , averaging 9 to 12 X's per string . SD runs from 4.2 to 6.0 , so I think I'm doing something right .
Press is a RCBS , RS2 , with a Redding , Type "S" , FL Bushing Die , followed by a .3075 Carbide Expander .
There is a minimal amount of "float" in the Ram , and I have seen no negative response from this "float". Rounds are within .0005 - .001 of TIR .
Reamer is a 2017 FTR Reamer with a slight modification , for a .190 Freebore .
I rarely have to trim Cases , maybe after four or five firings , to get them back to the 2.010 dimension I use .

 

[Wild Bill IV]

This may be unpopular but imho a zero set back might not be the best way to keep a rifle cycling after ignition, nothing good comes from fighting a bolt open during a relay or hunting when you need to send another round.
Additionally, .002 -.0025 is only the thickness of a human hair, that I can’t imagine being considered excess movement on brass causing shorten life span. I dont recall ever wearing out brass unless it’s primer pockets getting loose.

You are so right in the issue of zero bump vs bolt cycling!!!
This applies to the typical hunter as well as the target competitors!!!
Whoever, there are a few of us that try for perfection and compete against ourselves!!
NEAR PERFECT CASE TO CHAMBER GEOMETRY HAS NEAR PERFECT BULLET ALIGNMENT!!!!
I'm talking about the guy that pulls one round out of his shirt pocket, and ask his friends/family which rock on the steep slope they would like to see a cloud of dust come off of!!!! Slightly heavy bolt lift is no big deal for the 1 shot cold barrel shooter!!!

I'm a once and let it cool down shooter!!! In hunting, plinking, single shot varmint blasting, steel, and misc other target!!! Just need to know the height of the target for ranging purposes!!! The scope will tell me the distance to the target!!! I don't need a rangefinder, it is built into the scope if you know how to use it!!! It's simple math and a knowledge of optics!!!! Plus, verification of scope reticles and turret adjustment graduations is a requirement!!!

I hate to brag, but my hunting success is one round for every single tag!!! You take the shot if you are confident!!! You pass if the environment is unfavorable!!! I've past on huge Muley bucks at 500 with 25 mph winds 35 mph gusts!!! But a 10point whitetail in a very gentle morning breeze at near 600 (574 yards on 6° upward slope is ~ 600 aimpoint) dropped straight down with a double lung, semi high heart shot with a custom 25-06!!! I knew it was a heart shot!!! In the follow through, I seen the dust/hair ring and the red mist cloud inside the ring through the corner of the scope!! That was maximum effective range for that bullet type and animal and I hit around one inch higher than the aim point!!! A nice antelope buck was rolled at 450 (about an 8° uphill shot) in a terraced winter wheat section with a Remington 700 BDL Varmint Special in 7-08!!!!! With the tuned 7-08 rifle using the 160 SBT SGK, I could get under .1MOA with seven shots!! That was an easy tag to sign!! The secret to the cool and cold fall/wintet hunts is: keep 3 rounds in the shirt pocket with a heavy jacket or coat holding in the body heat!!! Load the round and fire it within 15 to 20 seconds!!! You range, find the firing solution, load and shoot!!! Cold rifles with cold rounds makes 500 yards shots tough and require backup up shots most of the time!!!!

This forum is mainly for the competitive shooter!!!
However, some of us members are hunter-shooters that utilize some aspects of the comp shooter!!! And sometimes, you have to customize a certain procedure or process for a specific different purpose!!!! Then test to see if it works!!!

 

[209jones]

Pretty simple stuff really, if you increase the shoulder bump, the firing pin will push the case forward that much extra, til it hits the shoulder on case and chamber, can affect ignition and cause misfires too, if the distance is too much, firing pins only extend so far. It will affect seating length on a rimless case that uses the shoulder to headspace, can also affect a belted case to a point, belts aren't all the same width.

 

[Wild Bill IV]

Pretty simple stuff really, if you increase the shoulder bump, the firing pin will push the case forward that much extra, til it hits the shoulder on case and chamber, can affect ignition and cause misfires too, if the distance is too much, firing pins only extend so far. It will affect seating length on a rimless case that uses the shoulder to headspace, can also affect a belted case to a point, belts aren't all the same width.

That's a very good point!!! Reducing the distance that the extractor pushes the case forward, increase the force, and area of primer pin strike!!
Another positive factor when looking at the geometry for reducing bump and getting more consistency and uniformity for primer ignition!!
Says the person (me) that files bases flat before uniforming primer pockets on virgin brass!!!
MANY MINDS AT WORK CAN LEAD TO POSITIVE RESULTS!!!
THAT'S THE POWER OF THE FORUM!!!!!!!!!!!!!!!!!!
THANK YOU 209jones!!!!!!!!

 

[dellet]

something else for the engineers to consider is bolt thrust. When you have clearance between the chamber and the case, two things happen. The case base to expand to the size of the chamber, out diameter and length. Diameter first, so before the bolt face has to absorb any pressure, the case has to stretch. Basically acting like a shock absorber. Without that dampening, the bolt face and locking mechanism takes full pressure. Maybe this concerns you, maybe not. But certain actions tolerate this better than others.

Below is the same load, one a fire forming with zero headspace, the other with .003”. The results show clearly on the primer and it’s probably not what most people think.

 

[JFrank]

I don’t have a see though chamber but I picture the ejector spring pushing the case rim against the extractor claw that’s holding the case from moving forward until the body stretches to allow the shoulder to make initial contact before moving back against the bolt face.

Am I wrong in this scenario ?

 

[lawebb21]

my opinion is that if the shoulder is bumped further and bullet seating die is unchanged then it will result in the bullet being closer to the lands (or jammed further if jamming) when the round is chambered.

 

[Evan]

I don’t have a see though chamber but I picture the ejector spring pushing the case rim against the extractor claw that’s holding the case from moving forward until the body stretches to allow the shoulder to make initial contact before moving back against the bolt face.

Am I wrong in this scenario ?

I’m pretty sure most rifles have more than a few thousandths of clearance on the extractor given the potential rim thickness variations that are possible. This would mean that the ejector would push the brass shoulder tight into the chamber (assuming the bullet is seated out of the lands and doesn’t stop the forward movement first, as compared to how you might for a hard-jam fireform).