Headspace and accuracy

[Brians356]

If your goal is to find out what they meant by excessive head space well .007 is on the right track.

If you mean "excessive headspace for best accuracy", few here would disagree.

"Excessive headspace" most commonly refers to dangerously excessive headspace. SAAMI specs typically allow for at least .010 headspace. Most factory ammo I've measured provides .008 headspace or more when chambered.
-

 

[M-61]

If you mean "excessive headspace" for best accuracy, few here would disagree.

"Excessive headspace" most commonly refers to dangerously excessive headspace. SAAMI specs typically allow for at least .010 headspace. Most factory ammo I've measured provides .008 headspace or more when chambered.
-

Yup. That's what I meant.
{as a side note my spell check changes headspace to two words for some reason}

 

[SheepDog]

The idea of having a cartridge that is substantially smaller than the chamber is foreign to me. Ideally I want a cartridge that has as close to a fit as I can get with reliable feeding. That means I would like to have the body of the case provide less than .001" (1/1000") difference in the diameter of the chamber. I would like less than .001" in case length to the shoulder than the chamber length to the shoulder, and I would like between .001 and .002" diameter difference in the neck of the case and the neck of the chamber. I want the free bore with less than .001" clearance for the bullet and a leade with a taper to the rifling of less than 2 degrees.

Since getting a die made to fit the case to the chamber with such close tolerances is impractical, if not impossible, I neck size only the front of the neck and let the cartridge spring back from the chamber to allow for the necessary clearances. I have tried full length sizing, partial full length sizing, and full neck sizing and partial neck sizing gives me the best results. I work my loads up with brass that has been partial neck sized and fired several times prior to the work up procedure. I choose my bullet for terminal ballistics on the game I hunt and my powder for the velocity necessary to drive the bullet fast enough to make the bullet perform at the ranges I shoot. I stay clear of maximum loads because they are not necessary for my use. I always start with the recommended overall length for bullet seating and rarely have to deviate from that to get sub MOA accuracy. In all the years of reloading this way I have never had to "bump" a shoulder back or had a round that grew too large in diameter to easily chamber.
I use all kinds of brass but most of it is Winchester brass purchased back in the 70s in bulk bags. I have a lot of military brass that is used in the 3006 and 358. The military brass has to have its own individual loads because of the smaller internal volume. Other than that, it is all treated the same.
I understand that other people have different techniques that work just as well for them and have no argument with that. Reloading is about trying different things to find what works for you. So, keep trying different things to find out what works for you in your guns and in the way you shoot.

 

[Shynloco]

My experience is that it can very from caliber to caliber, brass brand to brass brand, how many cycles on the brass, etc.. That said, and again in my experience, 0.007 is excessive that could havoc flyers (especially on older or non-annealed brass). Plus risks of "case head separation" and/or case fracture goes up when sizing that much.
Donovan

+1. Been there done that. The cure is simple, have the barrel take off, cut and re-chambered. With that excessive bump, I was experiencing indications of impending head separation at the second resizing of Lapua brass. Not wise at all to continue shooting that rifle in it's present form. Just my .02 worth.

Alex

 

[msinc]

The idea of having a cartridge that is substantially smaller than the chamber is foreign to me. Ideally I want a cartridge that has as close to a fit as I can get with reliable feeding..........

Amen, and why wouldn't you want/have this. I don't know where you guys are getting all this .008" under headspace length "factory" ammo or who is making it, but they must not sell it around here. Maybe it is something new they just started...admittedly, it's been years since I have purchased any factory ammo. But I have and it was always pretty spot on {it was always name brand stuff too}. I remember once having to load some new Remington brass cases for a rifle I had on a hunting trip to my brother-in-laws. I never sized any...just primed, charged and seated the bullet. They were dead on. Not saying they cant produce ammo that's way under size...just that I have been lucky enough to not see it, and that is unusual the way my luck runs!!!

 

[ireload2]

Dead on is not a quantifiable value unless you are claiming it is zero.
You should provide data to back up such statements.
You cannot provide data unless you measure the unfired cases.
Do you even have a way to measure unfired and fired cases?

Amen, and why wouldn't you want/have this. I don't know where you guys are getting all this .008" under headspace length "factory" ammo or who is making it, but they must not sell it around here. Maybe it is something new they just started...admittedly, it's been years since I have purchased any factory ammo. But I have and it was always pretty spot on {it was always name brand stuff too}. I remember once having to load some new Remington brass cases for a rifle I had on a hunting trip to my brother-in-laws. I never sized any...just primed, charged and seated the bullet. They were dead on. Not saying they cant produce ammo that's way under size...just that I have been lucky enough to not see it, and that is unusual the way my luck runs!!!

 

[T-shooter]

Amen, and why wouldn't you want/have this. I don't know where you guys are getting all this .008" under headspace length "factory" ammo or who is making it, but they must not sell it around here. Maybe it is something new they just started...admittedly, it's been years since I have purchased any factory ammo. But I have and it was always pretty spot on {it was always name brand stuff too}. I remember once having to load some new Remington brass cases for a rifle I had on a hunting trip to my brother-in-laws. I never sized any...just primed, charged and seated the bullet. They were dead on. Not saying they cant produce ammo that's way under size...just that I have been lucky enough to not see it, and that is unusual the way my luck runs!!!

I recently saw some Hornady A-Max factory loads for an AR that were .012" under a Forster headspace gauge which is about .002" shorter than my chamber. That's beyond loose!

 

[msinc]

Dead on is not a quantifiable value unless you are claiming it is zero.
You should provide data to back up such statements.
You cannot provide data unless you measure the unfired cases.
Do you even have a way to measure unfired and fired cases?

Hittin' the Bushmill's early today are we????? I took the empty new cases and with the bolt disassembled it just cammed over on the cases in my chamber...same as it did when I headspaced the rifle on the go-gauge.....best I could do at someone else's house...is that data "dead on" enough for you. Like it or not, it worked and it worked great for me. I did not fire them all, I did also check the ones I didn't fire when I got home with my gauge. I did not include this information on that particular post because I really didn't think someone would be petty enough to bawl about it. I should have known better, I will make certain I absolutely prove every word for your personal edification next time....wait, no...on second thought I could care less what you think!!!!

 

[Brians356]

I don't know where you guys are getting all this .008" under headspace length "factory" ammo or who is making it, but they must not sell it around here. Maybe it is something new they just started...admittedly, it's been years since I have purchased any factory ammo.

That may explain it, but I doubt factory ammo specs have changed. Where am I getting it? Every factory round I've measured has been at least .007" shorter than fired cases as measured using a Hornady headspace gauge. Not surprisingly since as I explained earlier, SAAMI specs allow for .010" and more headspace for every rifle cartridge spec I've checked. Manufacturers have tended toward the short (but still safe) side to assure rounds will chamber with room to spare. They simply must size shorter than SAAMI Min Chamber to achieve that.
-

 

[msinc]

That may explain it, but I doubt factory ammo specs have changed. Where am I getting it? Every factory round I've measured has been at least .007" shorter than fired cases as measured using a Hornady headspace gauge. Not surprisingly since as I explained earlier, SAAMI specs allow for .010" and more headspace for every rifle cartridge spec I've checked. Manufacturers have tended toward the short (but still safe) side to assure rounds will chamber with room to spare. They simply must size shorter than SAAMI Min Chamber to achieve that.
-

I get it, and I am not saying that new ammo cannot be under size. I just have not seen any with some of the under size specs I am reading about on this forum. In regards to headspace, there is "ideal" and then there is what I call "workable", it's kind of like the Army using a field gauge that is double what a "no-go" gauge is...they are not reloading, it is intended that their brass cases end up being left laying on the ground and forgotten about. Fire it once and forget about it. That is also the case with factory ammo...the factory ammo we buy in a store is not sold with any intent of ability to be reloaded implied. These same manufacturers are so afraid of liability that you almost cant buy a gun with a less than 8 pound trigger, but the ammo they make is way out of spec????
Also, undersized cases is one of the reasons why I believe "once fired" brass is not necessarily the great deal people think it is...it may be only fired once, but you don't know how far it had to stretch to get blown out to fit the chamber. Even if you do have the tools to measure a fired case you still don't know what the case measured before it was fired. You might be better off with cases that are on their third firing but were on size and not sized but a few thousandths each time.
What blows me away is that we, on this forum at least, are not operating like the Army...no, we have a rifle built and why would any gunsmith not headspace it so it did anything less than just cam over on a go-gauge??? Now, couple that with the fact that just about everyone on here is also reloading custom accuracy oriented ammo and sizing to just fit that chamber. Even if the chamber is not minimum SAAMI there is still a very high probability the ammo is sized to the chamber, yet guys get on here and talk about firing a rifle with ammo that is .012"-.015" under size??????? Has something happened I missed that rendered case head separations completely safe these days????? It has to be me, I have to be missing something because the gauges I build rifles to have a .004" range. Throw in some .015" short ammo in a maximum chamber and the comment is not "don't do it" it's "yeah, the firing pin should still set it off"??????? I am lost on this one guys.

 

[Brians356]

These same manufacturers are so afraid of liability that you almost cant buy a gun with a less than 8 pound trigger, but the ammo they make is way out of spec????

I've been trying, but not hard enough I guess.

Factory ammo is not "out of spec". Trot out a modern factory round that measures shorter than SAAMI Min Cartridge length at the datum. Just one.

I haven't encountered a new centerfire rifle in many years sporting an 8-lb trigger, or even close, but I've doubtless just been very lucky.
-

 

[T-shooter]

I've been trying, but not hard enough I guess.

Factory ammo is not "out of spec". Trot out a modern factory round that measures shorter than SAAMI Min Cartridge length at the datum. Just one.

I haven't encountered a new centerfire rifle in many years sporting an 8-lb trigger, or even close, but I've doubtless just been very lucky.
-

I haven't used factory ammo in years. I never did and started with new cases and reloaded when I built my AR. I was helping a friend set up his press for .223's. He was using a factory Hornady A-Max round as the specs to set the resizing die. Way off. My Forster headspace gauge fit his chamber and with a .002" piece of tape on the rear, took a lot of pressure to push the bolt closed with my thumb. (I'm sure the tape gave a little). Checking the die (without the tape) in the Hornady comparator, the factory round was .012" shorter. After getting him set up and allowing .003 (for a semi-auto) under the headspace gauge, the rounds chambered easily.

Factory ammo is made to fit .223 and 5.56 chambers. It has to fit rifles from every manufacturer and probably is sized to run in a fully automatic too with looser chambers.

Factory triggers are another thing. I always rework them. My .308 has a 1-3/4 lb trigger. My AR is at 4 lbs. Pistols are the worst offenders. I did a couple triggers on a pair of S&W Sigma 9mm's. They were in the 14+ lb range. Took them down to 6 lbs which is enough and still maintains a reasonably amount of safety.

 

[Brians356]

I have to be missing something because the gauges I build rifles to have a .004" range. Throw in some .015" short ammo in a maximum chamber and the comment is not "don't do it" it's "yeah, the firing pin should still set it off"??????? I am lost on this one guys.

As long as the cartridge is at least SAAMI Min length at the datum, it will fire safely in that SAAMI Max chamber. If it doesn't, likely either the charge or primer has gone bad, or there's something amiss with the firing pin or spring.
-

 

[rain164845]

To Anbar the question, it did not get rid of my flyers and accuracy was about the same. 200 yard targets. More headspace on the left.
Also, No sign of case head seperation

 

[Brians356]

it did not get rid of my flyers and accuracy was about the same. 200 yard targets. More headspace on the left.
Also, No sign of case head seperation

I don't see any flyers.

With the headspace you reported, well within SAAMI spec, and not yet a large number of FL resizings, I would not even have been looking for incipient head separations.
-

 

[bsekf]

Some BR guys FL every time. I have never understood that. I would not want to change the case dimension, so I would just neck or collet resize. Now, I would understand if they indexed, like the single shot guys, but that is hard to do in a bolt gun. Maybe, FL is the bolt gun answer to indexing, making every case the same???????? HUMMM

Bill

 

[T-shooter]

Some BR guys FL every time. I have never understood that. I would not want to change the case dimension, so I would just neck or collet resize. Now, I would understand if they indexed, like the single shot guys, but that is hard to do in a bolt gun. Maybe, FL is the bolt gun answer to indexing, making every case the same???????? HUMMM

Bill

I do now but can't say if it's better or worse. Sounds like another test to me. I set the necks back no more that .001". I measured how much the dies compressed the case over a fired case. This measurement was with stock dies. I polished the inside of the Forster mostly at the top which should have taken a couple 10/1000's off. I haven't remeasured but probably about .0005" on a side compression at the top under the shoulder using Lapua brass.

 

[Canadian bushman]

In my personal experience headspace has a significant effect on a cartridges performance. This is especially true when the headspace becomes a very close or a interference fit.

A load that is in tune at .002 bump may perform unpredictably when the case becomes tight in the chamber. This is also true in reverse.

Ive also noticed that once you have significant clearance .002-.003, the changes in the load become less noticeable with small variations in headspace.

This same idea seems to apply to the head of a cartridge as well. These clearances need to remain consistent as well or you may watch your load jump around earlier than you may expect as you work through your first 4-5 firings.

As far as factory chambers and ammo go. Factory rifles seem to usually be cut toward the middle or high of the saami tolerance and ammo seems to usually favor the low of the tolerance. Typically this creates about .005-.015 of clearance. By no means is this unsafe. Its the same conditions as tested by saami. Its just not the best scenario for brass life.

 

[BoydAllen]

The idea of having a cartridge that is substantially smaller than the chamber is foreign to me. Ideally I want a cartridge that has as close to a fit as I can get with reliable feeding. That means I would like to have the body of the case provide less than .001" (1/1000") difference in the diameter of the chamber. I would like less than .001" in case length to the shoulder than the chamber length to the shoulder, and I would like between .001 and .002" diameter difference in the neck of the case and the neck of the chamber. I want the free bore with less than .001" clearance for the bullet and a leade with a taper to the rifling of less than 2 degrees.

Since getting a die made to fit the case to the chamber with such close tolerances is impractical, if not impossible, I neck size only the front of the neck and let the cartridge spring back from the chamber to allow for the necessary clearances. I have tried full length sizing, partial full length sizing, and full neck sizing and partial neck sizing gives me the best results. I work my loads up with brass that has been partial neck sized and fired several times prior to the work up procedure. I choose my bullet for terminal ballistics on the game I hunt and my powder for the velocity necessary to drive the bullet fast enough to make the bullet perform at the ranges I shoot. I stay clear of maximum loads because they are not necessary for my use. I always start with the recommended overall length for bullet seating and rarely have to deviate from that to get sub MOA accuracy. In all the years of reloading this way I have never had to "bump" a shoulder back or had a round that grew too large in diameter to easily chamber.
I use all kinds of brass but most of it is Winchester brass purchased back in the 70s in bulk bags. I have a lot of military brass that is used in the 3006 and 358. The military brass has to have its own individual loads because of the smaller internal volume. Other than that, it is all treated the same.
I understand that other people have different techniques that work just as well for them and have no argument with that. Reloading is about trying different things to find what works for you. So, keep trying different things to find out what works for you in your guns and in the way you shoot.

While your statement about what has worked best for you cannot be challenged, some of the rest of what you have written might bear examination. let us consider first what we may best use as a reference for what works best for accuracy. For this I will specify sanctioned short range group benchrest. The current thought by some of the best in this sport favors neck to chamber clearance in the range of between .002 and .003. With regard to case body to chamber fit at the shoulder I would refer you one (I forget which) of the Jack Neary instructional videos on Youtube. There are six. As far as your assertion as to the difficulty of matching FL dies to chambers goes, competitors in this sport do it all the time. All it takes is a little money, and in many cases not that much. Beyond that sport I have helped to design several tight neck reamers using sized cases from one piece FL dies as a reference. Using that method I have been able to easily control loaded round to chamber clearances, since I know the dimensions of the sized brass. Similarly, neck diameter, thickness, clearance and tension are easy to calculate. In any case, I am favor of experimentation and letting ones targets be the final determining factor. Beyond that, I have seen more than one approach work, so this is not to contradict what you wrote, but simply to add additional information.

 

[Webster]

I have a control group of 10 cases at .007 and 10 at .0015. I hope to test them this weekend. I am hoping this fixes my flyers.

If you know 0.007" is improper why are you wasting you time testing it?