head space and accuracy

[gilmillan1]

hello,

I have been reloading for about 2 years now. I do some f class shooting too, and it seems there is always something new to learn in this business.

i always heard about shoulder bumping but i never paid that much attention. it seems that something clicked in my mind and now it seems it does matter.

the question is, how much does proper head space impact accuracy? and how much head space is ideal for accuracy? it seems every where I see that 2 thousands is good, but i dont know.

lastly, can you bump a shoulder with a redding neck bushing sizing die?

thanks

Gil

 

[jonbearman]

Yes you can bump it with the die you have by removing the bushing and carefully adjusting the die till you get the bump you want. You will need the hornady headspace kit to measure with to get it right. It will improve accuracy with a .002 thou bump if you need it.The rifle will tell you when it gets hard to chamber a round and the bolt closes stiffly. Disregard my input on using the neck die to bump the shoulder. Donavan is right. I appreciate you correcting me Donavan because we all need too from time to time.

 

[Tim Singleton]

This is how i size ppc brass. I learned this from reading Tony Boyer's book
Remove your firing pin and adjust head space on your brass until you have a slight resistance just as the bolt closes. If the bolt falls closed with no resistance your sizing to much. If you feel resistance at more than half way on closing it's not sized enough.

As someone posted on the other day as brass gets more and more firings it hardens at different rates. So when going to a competition I remove firing pin and sort through my brass to group as set together that all feel the same

Also a neck die is not designed to size the shoulder or body.

For what it's worth

Tim

 

[jonbearman]

There was a thread here saying you could but if I am wrong then I am wrong. I don't know why there wouldn't be a shoulder in a neck die to begin with either. I agree a bump die is the way to go. I must have misunderstood what was written.

 

[dixieppc]

There was a thread here saying you could but if I am wrong then I am wrong. I don't know why there wouldn't be a shoulder in a neck die to begin with either. I agree a bump die is the way to go. I must have misunderstood what was written.

For each new chambered barrel, I always send Harrell 3 fully fire formed cases so he can make me a minimum FL/Bump die that also uses neck bushings to size the neck at the same time. Each die also comes with a bump gauge for that specific fired case. I always keep my brass bumped to a point to where my bolt (with firing pin removed) will fall half way down before meeting light resistance. This way my case will always be pushed back against the bolt face but not offer enough resistance to upset the rifle on the rest when closing the bolt.

Harrell FL/Bump/Neck Die
http://harrellsprec.com/index.php/products/full-length-die

Regards.....

 

[22BRGUY]

Jon I believe Donovan is correct on this because in the process of bumping the shoulder, the body also needs to be resized at least somewhat or the brass would be pushed outward making the case difficult to chamber. I learned it the hard way.

 

[jonbearman]

I get that know and concede to be well informed now. I didn't even think that was the problem but now I see what you mean.

 

[bigedp51]

gilmillan1

If you full length resize by the die directions, meaning the die is making hard contact with the shell holder and the press cams over you can push the shoulder back too far and create excess head clearance.

Below is an animated image of a cartridge being fired, the firing pin pushes the case forward until the shoulder of the case contacts the shoulder area of the chamber and the cartridge goes bang. As pressure builds it pushes the primer out of the primer pocket and the cartridge case grips the chamber walls. As the pressure increases it reaches the elastic limits of the brass and the case stretches to meet the bolt face. If the shoulder is bumped back too far the case will stretch and thin in the base web area and this leads to case head separations. This where the .001 to .002 shoulder bump come into play, with this minimum of head clearance the brass will not stretch and thin and the brass will try to spring back to its original shape

With a Hornady cartridge case headspace gauge or the RCBS precision mic you measure your fired length and then bump the shoulder back .001 to .002 shorter than the cases fired length for maximum case life.

A full length resized case is supported by the bolt face in the rear and by the bullet the the chamber throat. This greatly reduces any cartridge case misalignment with the chamber and the bullet elignment with the bore.

On the flip side of this you have the shooters who prefer neck sizing only but this requires higher quality brass with more uniform case wall thicknesses. And I prefer to full length resize my cases.

 

[gilmillan1]

thank you guys for the replies. i know have a better understanding of headspace. thank you

 

[ptf18]

bigedp51: Thank you for the illustrations. We get a better understanding when things like this are shown to us.

I shoot NRA High Power matches.

The OP asked and I would like to know also on the "average" how much accuracy is gained/lost with with "excssive" headspace?

Im always concerned about reliablity ie, not being able to chamber a cartridge when Im "on the line" especially after firing many rounds and not being able to clean the rifle between stages.

 

[gilmillan1]

I am with ptf18 on this one. anyone?

 

[dkhunt14]

Every 1000 yard benchrest and short range benchrest guy I know full length sizes. It doesn't hurt accuracy or they would be neck sizing. You have to be able to open the bolt and close without upsetting gun. You can only do that with brass that has been sized. They usually bump about .002. Matt

 

[Tim Singleton]

In short range benchrest and probably holds true in other competition as well
We load fairly hot There is really no choice but to full length size a small amount .001-.002. The cases simply won't re chamber if we neck sized only

 

[bigedp51]

bigedp51: Thank you for the illustrations. We get a better understanding when things like this are shown to us.

I shoot NRA High Power matches.

The OP asked and I would like to know also on the "average" how much accuracy is gained/lost with with "excssive" headspace?

Im always concerned about reliablity ie, not being able to chamber a cartridge when Im "on the line" especially after firing many rounds and not being able to clean the rifle between stages.

The biggest problem with "excess" headspace is the case stretching and warping on firing and then causing misalignment of the case with the bore when reloaded. Once the elastic limits of the brass is reached and the brass stretches excessively the case will be warped and banana shaped. This is why you see so many shooters recommending .001 to .002 shoulder bump because it does not over stress the brass.

The OP also said "accuracy" and "headspace" and the quality of your brass has more to do with this than "headspace" does. The cartridge case expands in two directions when fired, in diameter to meet the chamber walls and in length to meet the bolt face. Any cartridge with unequal case wall thicknesses can warp when fired and resizing makes this worse because the base of the case is no longer 90 degrees to the axis of the bore.

And this is where full length resizing comes into play by minimizing these case abnormalities and misalignment with the bore. Meaning if the case doesn't touch the chamber walls it can't steer the bullet off center with bore alignment.

And now a word from Team Lapua USA, and someone with far, far more experience than I have on the subject.

The .308 cases below were full length resized as per the die manufactures instructions meaning with the shell holder making hard contact with the base of the die and the press reaching cam over. Meaning far more shoulder bump than .001 to .002 and the cases stretching excessively leading to case head separations. The problem with the information below was a new Savage .308 rifle was used "but' the rifles actual headspace was not given nor was the total shoulder setback or shoulder bump given, so the information below is "ball park" and can vary between any firearm.

Also please note the stretch figures of the brass below the number of times the case was fired and when the case failed. So again this is why minimum shoulder bump helps prevent case stretching and "distortion" and extends case life.

Bottom line, the quality and uniformity of your cartridge cases equals accuracy, and "minimum" full length resizing can remove minor case flaws from the equation.

And over resizing brass with unequal case wall thickness gives new meaning to "getting bent". ;D

Below a warped banana shaped case with the base of the case no longer 90 degrees to the axis of the bore, The case stretching caused the case to warp and stretch and failing after two reloadings in a fat and long military chamber. (excessive shoulder bump)

 

[Joe R]

Tim Singleton said: This is how i size ppc brass. I learned this from reading Tony Boyer's book
Remove your firing pin and adjust head space on your brass until you have a slight resistance just as the bolt closes. If the bolt falls closed with no resistance your sizing to much. If you feel resistance at more than half way on closing it's not sized enough.

As someone posted on the other day as brass gets more and more firings it hardens at different rates. So when going to a competition I remove firing pin and sort through my brass to group as set together that all feel the same

Also a neck die is not designed to size the shoulder or body.

For what it's worth

Tim

Here's the page and picture that Tim is talking about.

 

[22BRGUY]

Tim Singleton said: This is how i size ppc brass. I learned this from reading Tony Boyer's book
Remove your firing pin and adjust head space on your brass until you have a slight resistance just as the bolt closes. If the bolt falls closed with no resistance your sizing to much. If you feel resistance at more than half way on closing it's not sized enough.

As someone posted on the other day as brass gets more and more firings it hardens at different rates. So when going to a competition I remove firing pin and sort through my brass to group as set together that all feel the same

Also a neck die is not designed to size the shoulder or body.

For what it's worth

Tim

Here's the page and picture that Tim is talking about.

Thanks for the excellent pic and info Joe as well as the other good posts also. One additional "fly in the ointment" that may come into play here that I have experienced, is that if you are resizing your cases and noticing shoulder bump with a bushing style FL die, I've discovered that a bushing style die will not size the case neck all the way down to the neck shoulder junction, but leaves a small portion of the neck just ahead of that point unsized. What can happen if you use this type of case that is not resized all the way down, is that when closing the bolt as mentioned to a point where you see or feel resistance, you may actually be seeing/feeling resistance from the unsized portion of the case neck fitting into the chamber neck of the rifle rather than from the case shoulder umping up against the chamber.. The best and only solution I can think of to solve this possibility, is to use a non-bushing type FL die at least to determine the correct amount of shoulder bump when closing the bolt as described. If others have had different experiences with this, I welcome hearing about it. Best Wishes all.

 

[Tim Singleton]

Tim Singleton said: This is how i size ppc brass. I learned this from reading Tony Boyer's book
Remove your firing pin and adjust head space on your brass until you have a slight resistance just as the bolt closes. If the bolt falls closed with no resistance your sizing to much. If you feel resistance at more than half way on closing it's not sized enough.

As someone posted on the other day as brass gets more and more firings it hardens at different rates. So when going to a competition I remove firing pin and sort through my brass to group as set together that all feel the same

Also a neck die is not designed to size the shoulder or body.

For what it's worth

Tim

Here's the page and picture that Tim is talking about.

Thanks for the excellent pic and info Joe as well as the other good posts also. One additional "fly in the ointment" that may come into play here that I have experienced, is that if you are resizing your cases and noticing shoulder bump with a bushing style FL die, I've discovered that a bushing style die will not size the case neck all the way down to the neck shoulder junction, but leaves a small portion of the neck just ahead of that point unsized. What can happen if you use this type of case that is not resized all the way down, is that when closing the bolt as mentioned to a point where you see or feel resistance, you may actually be seeing/feeling resistance from the unsized portion of the case neck fitting into the chamber neck of the rifle rather than from the case shoulder umping up against the chamber.. The best and only solution I can think of to solve this possibility, is to use a non-bushing type FL die at least to determine the correct amount of shoulder bump when closing the bolt as described. If others have had different experiences with this, I welcome hearing about it. Best Wishes all.

Your observation is correct as far as the bushings do not size the neck all the way down. What you have to remember is even an unsized fired case neck will mic smaller than the chamber neck dimension. Due to spring back. My ppc fired cases mic .2615 for my .262 neck chamber which very well could be .2625
The small section of un sized neck remains the same no matter how much you bump the shoulder. If you bump to much the bolt will fall closed offering no resistance. You can't feel the unsized portion of neck

 

[mikecr]

You can rechamber cases that have not been neck sized at all.
Partial neck sizing won't change this. So the feeling of unloaded bolt turn method works.
You can also measure fired shoulders and then bump back ~1thou as measured. cycle through chamber to confirm feel is good.

On bumping, I measure every single case, every time. This, because cases do not all take bumps the same(different springback), and even a slight difference in lube can affects results.
Also, brass counters last sizing action over time(everywhere sized).
So if you bump cases today and then let them sit for months before reloading -better check bump again. Given this, for hunting cartridges that I keep in safe-stock most of a year, I bump 1.5thou(extra half).

 

[BoydAllen]

Generally speaking, with a known fit between chamber and FL die, setting dies by feel can work, but for many, less experienced reloaders, and for tight chambers there can be a problem. The die can be too large for the chamber, and by the time that the desired bolt feel is obtained, the shoulder has been pushed back too far.
For example:
Friends both had slow twist 6BR barrels chambered for well built custom varmint rifles. The work was done by reputable gunsmiths, using custom dimensioned reamers. While they were in the process of having the work done, I told both that because their chambers were likely to be smaller in the back than standard, that they would be better off ordering FL dies from Harrell's Presision, instead of ordering a similar die from Redding. (I had run into a situation where a Redding S type FL die did not size the back of cases from a tight necked .222 that had been chambered with a match dimensioned reamer that was smaller in the back than factory.) Both friends, being familiar with Redding dies, and not being familiar with Harrell's, ignored my warning, and after they had both their rifles and the dies in hand, discovered that the problem that I had cautioned them had come to pass. By the time that they had adjusted their dies down far enough to size the backs of their cases, the cases' shoulders had been pushed too far back. After that, they both sent in fired cases to Harrell's, and promptly recieved the dies that they have used ever since. This is why I tell people to get the proper tool(s) and always measure shoulder bump, because unlike Tony Boyer, who knows that his die is suitable for his chamber, we have no idea if that is the case when someone posts a question as to how to properly set a die.

Some years ago, a good friend that I had told he should be measuring, disagreed, saying that he had been setting by feel for years, so I challenged him to a test. I asked him to unset and reset his die several times, and bring the resultant sized cases over to my house to be measured using my recently acquired Stoney Point (now Hornady) caliper attachment. He did as I requested, and the measurements were all over the place, much less consistent than he would have imagined. At that point he went home and made some gauges for various calibers that were similar to the one that Harrell's furnishes with their dies.

 

[22BRGUY]

Tim Singleton said: This is how i size ppc brass. I learned this from reading Tony Boyer's book
Remove your firing pin and adjust head space on your brass until you have a slight resistance just as the bolt closes. If the bolt falls closed with no resistance your sizing to much. If you feel resistance at more than half way on closing it's not sized enough.

As someone posted on the other day as brass gets more and more firings it hardens at different rates. So when going to a competition I remove firing pin and sort through my brass to group as set together that all feel the same

Also a neck die is not designed to size the shoulder or body.

For what it's worth

Tim

Here's the page and picture that Tim is talking about.

Thanks for the excellent pic and info Joe as well as the other good posts also. One additional "fly in the ointment" that may come into play here that I have experienced, is that if you are resizing your cases and noticing shoulder bump with a bushing style FL die, I've discovered that a bushing style die will not size the case neck all the way down to the neck shoulder junction, but leaves a small portion of the neck just ahead of that point unsized. What can happen if you use this type of case that is not resized all the way down, is that when closing the bolt as mentioned to a point where you see or feel resistance, you may actually be seeing/feeling resistance from the unsized portion of the case neck fitting into the chamber neck of the rifle rather than from the case shoulder umping up against the chamber.. The best and only solution I can think of to solve this possibility, is to use a non-bushing type FL die at least to determine the correct amount of shoulder bump when closing the bolt as described. If others have had different experiences with this, I welcome hearing about it. Best Wishes all.

Your observation is correct as far as the bushings do not size the neck all the way down. What you have to remember is even an unsized fired case neck will mic smaller than the chamber neck dimension. Due to spring back. My ppc fired cases mic .2615 for my .262 neck chamber which very well could be .2625
The small section of un sized neck remains the same no matter how much you bump the shoulder. If you bump to much the bolt will fall closed offering no resistance. You can't feel the unsized portion of neck

Thanks Tim and I know what you are saying. The reason I posted what I did is because just yesterday and after reading this post, I thought just for the fun of it I'd make sure I was bumping correctly with a 22br of mine. I removed the firing pin from the bolt and proceeded to check headspace with one of my normally 1 thou bumped cases. I bump shoulders with a Redding FL type S with the bushing removed and the use a Lee modified collet die to partial size the necks almost all the way done. Lastly, I run a .223 expander inside the neck to end up with about 1 thou neck tension. These cases would not chamber much without resistance. I went back and further bumped back the shoulder another thou....same resistance., and another thou, same resistance. Thus my post on the subject. The chamber had also just been cleaned with JB for carbon as well. I trust your info and those of you that have much more experience than me in the competition game, but for whatever reason this is what I experienced yesterday. I also agree with Mike on checking each case individually. I just posted an article a couple of days ago about shoulder bumping and needing to adjust the die from time to time because some cases were needing slightly more or less sizing to get to the
same headspace dimension. I think it is because of the difference in "springback" as Mike said. Thanks all again.