Headspace query

[alzerh]

Hi there and Happy Holidays to you all

I started hand-loading for my 6BR and 260 Rem earlier this year and have had some great success at getting my groups down...ie. I'm not a total beginner but appreciate I still have a lot to learn. One query/issue that I have relates to headspace. When setting-up my sizing dies, I was told to 'bump the shoulder' back of my fire-formed cases by 1 thousandth of an inch. However, when I measured 25 of my new cases, the headspace ranged by 4.5 thousandths between the longest and shortest cases. After firing the cases, I was expecting them to all be the same headspace length since they would have formed to the chamber of my rifle on firing. However, when I measured 25 of my 1x fire-formed cases, the headspace still ranged by 4 thousandths between the longest and the shortest cases (albeit with a 1.5 thousandth longer average headspace than the new cases). So my question is this....when I set the die to bump-back the shoulder back by 1 thousandth, which headspace length am I measuring from? Do I bump-back 1 thousandth from the longest fire-formed case length I have measured (and if so, the majority of the cases won't be bumped at all since the shoulder won't reach the die), the shortest case length (which will form ALL the cases to the same length), or the average case length of my fire-formed data-set?

Also, separate but related question, is it possible to increase headspace length of a case when put in a sizing die (ie. can the case get stretched by a few thousandths)? The reason I ask is that I was told to calculate the headspace of my chamber by sizing a case and finding out what length of case made it hard for the bolt to close....if all of my cases are smaller than my chamber, I need to gradually increase the length of a case to figure-out when the bolt becomes difficult to close and this would represent the headspace length of my chamber.

All help greatly appreciated as I look to move up the learning curve!

Alzerh

 

[noload]

It seems a bit strange that your fired cases are still .004" different in bump shoulder length. I have to ask if you have the proper head space on you gun. If the head space is correct then you should have most of your fired cases blown out to proper head space length. If they are not all within .001". Something else is going on ??? You have to measure you Head space using a shoulder bump gage . The only way to increase your head space length is to blow it out in the chamber, its not made longer per say in the die, though the case may grow in length when sized, the shoulder will be bumped shorter. Your New cases should all blowout to the same head space length, if they don't, may be your load is too light. Your may have to give us more info to work with, like you load for instance, My first thing to do would be to confirm that you have proper head space in your chamber.

 

[RegionRat]

Don't give up yet. You should consider tracking those dimensions over several firing cycles before you make your estimate of the chamber shoulder datum based on fired case length. It takes more than one cycle on a new case to fire form to the chamber. There are many variables including the pressure of your load and the chamber heating.

It is worth the trouble to stay with it on those cases. There are also indications like taking the longest ones, empty and clean but not sized, and seeing if you can close the bolt on them. If it closes easy, don't expect them to give you that shoulder datum dimension yet. Does that make any sense, it isn't easy to explain....

Even sizing just the necks can move the shoulders depending on your dies and process. Check some samples before and after.

Don't bump the shoulders for several cycles and check the ability to close the bolt, when it starts to get tight, those numbers should start grouping and changing less.

 

['Freak]

It’ll take a couple or three full power loads to have the cases blown out enough to completely fill the chamber. Until then try to set the die so it will touch but necessarily setback the shoulder of your longest case.

Assuming you’re using a full length die and that it does size down the case body, in doing so it might also move the shoulder forward a bit on cases that were short of reaching the die’s shoulder to begin with.

When feeling out case length via closing the bolt on sized brass, it’s best done after you have removed the firing pin and ejector.

 

[LHSmith]

As mentioned, it takes several firings in the upper load region to fully fireform to your chamber. Also, applying case lube evenly to the case is critical. You'll even find a slight difference in measurement if other lubes are used .
Slight differences are the norm, as all cases will not "fireform" the same even though they saw the same number of firings using identical loads.
What tool are you using to measure H/S? Try several readings on the same case until you become proficient at it. Make sure the fired primers are removed.
Lastly, I prefer 0.002" H/S, even on Comp guns as I see no impact on accuracy and it gives less disturbance in the bags. I size just past the point where the bolt drops half way down, I prefer it to fall just before it bottoms out - done with the FP assembly removed.

 

[Road_Clam]

Thanks for the detailed info, I was under the impression that you get a fire formed case after a single firing. I too was wondering why my fire formed shoulder #'s were varying about .003" using my LW headspace height gage.

 

[MagnumManiac]

The difference in your measurements is not caused by your methods, it is due to the properties of brass hardness and how it 'springs back' after the firing sequence. The annealing process is never the same between cases, due to differences in alloy distribution throughout the case and impurities.
I wouldn't stress it, but get into a habit of 'hovering' at the top of the sizing stroke and pausing a few seconds before lowering the ram.
Hope this helps.

Cheers.

 

[Patch700]

I would agree with the above with regards to differing brass hardness and it's affect on bump.

Before we had access to such neat tools as shell holders with varying deck heights I used to make my own by bedding if you will the specific die to a specific shell holder.. I've since switched to a PMA lock ring as it allows me to quickly and accurately adjust the amount of bump within a group of brass that may or may not have slight differences in brass hardness.

And you are correct in assuming that base to datum length can be increased if not closely monitored when using a FL die.

 

[alzerh]

Many thanks to all of you for your responses and helpful guidance. All of what you say is understood and makes sense - essentially I need to continue to measure headspace as I reload and fire-form multiple times and the cases will eventually move towards the datum of my chamber and at this point I can consistently 'bump back the shoulder' by 1 to 2 thousandths. Until that point, when resizing my cases I will focus on minimizing run-out and getting the right neck tension for consistent bullet seating.

I do have one follow-on question, which actually drove my original query. I have read articles by well respected handloaders such as German Salazar and Jacob Gottfredson (http://www.6mmbr.com/JGcaseprep.html) and they describe the case-prep methodology for new cases to maximize accuracy. The first step is to full-length size and 'make the headspace identical for all cases'.

Based on my own experience described above, helpfully explained in your responses, getting 'identical headspace' cannot be achieved for new cases, correct? Hence, re-sizing cases as the first-step of the new case prep methodology would appear to be redundant, since the headspace could still vary by 4 to 5 thousandths after the sizing?

My goal here is it make sure my understanding of headspace in the handloading process is correct and also determine what is important and what is not....there so much information out there and I'm trying to find the quickest way to move up the learning curve...which I know is a long way but also half the fun, right?! Thanks again for your help.

 

[BoydAllen]

This is what I do. On new brass, I may run an expander mandrel in the necks to round up and uniform the neck tension. Some cases are known to have excessive neck tension as then come, so using an expander mandrel deals with this issue, and gives superior runout to that obtained using sizing dies' expanders. If the cases are unchamfered, I will do that, so that bullet seating can be done without scarring bullets. If I am forced to reload once fired brass, I set my FL die to reproduce the head to shoulder (measured with primer removed) dimension of the longest (in this dimension) fired case. If I have the opportunity, I do my loading at the range, and start out by firing a single case, sizing the neck only enough to hold a bullet, until the head to shoulder dimension reaches its maximum. I do this with stout loads, as hot as I can be sure will not damage the case. When I have a stable, maximum dimension, I record it, for that rifle, or if I have multiple barrels for a rifle, for that barrel. It is this dimension that I bump back from. As far as being able to make the head to shoulder dimension increase by FL sizing goes, yes it can be done, with a die that reduces the diameter of the body, and the die set so that its shoulder does not make contact with that of the case being sized. If you are carefully adjusting a FL die, a little at a time, and checking "headspace" as you go, you will see this. At some point, the dimension will increase above the fired measurement, and as you continue to screw the die into the press, the die will start to move the shoulder down, as it makes contact at the top of the ram stroke.

 

[alzerh]

Many thanks BoydAllen...this is what I have been doing with the new brass and makes sense to me. Actually, the 260Rem Lapua brass I have is so tight at the neck that I could not even seat any bullets without damaging them, hence the expander mandrel step was critical in this 'case' (pun intended!). Do you also go through a neck-turning step to iron-out any kinks that have been moved to the outside of the neck after expanding on the mandrel?

 

[BoydAllen]

I have a rule against owning field rifles that require neck turning, and have not found it necessary for those applications, BUT for my bench rifles, with tight necked chambers, I do, speaking of which, I have been evaluating a PMA Tool turning tool, and expander die, with carbide everything, and it is really fine.

 

[Brians356]

The difference in your measurements is not caused by your methods, it is due to the properties of brass hardness and how it 'springs back' after the firing sequence. The annealing process is never the same between cases, due to differences in alloy distribution throughout the case and impurities.

I believe the construction of the action and bolt are possible contributing variables, but not likely to be relevant in this context. But more than just the brass can deflect (however slightly) and spring back.

 

[fguffey]

[quot

Also, separate but related question, is it possible to increase headspace length of a case when put in a sizing die (ie. can the case get stretched by a few thousandths)? The reason I ask is that I was told to calculate the headspace of my chamber by sizing a case and finding out what length of case made it hard for the bolt to close....if all of my cases are smaller than my chamber, I need to gradually increase the length of a case to figure-out when the bolt becomes difficult to close and this would represent the headspace length of my chamber][/quote]
'
Yes there is a way, become a case forming reloader. Stretching a case is the method used by reloaders, to stretch a case a reloader fires it. When firing and stretching there is a problem reloaders have trouble keeping up with. Fire forming: I am not a fire former, to fire form a reloader chambers a round then pulls the trigger and immediately gets promoted 'FIRE FORMING STATUS'.

Longer cases: My favorite is the 280 Remington, it is .041" longer than the 30/06 case and its shoulder is .051" ahead of the 30/06. The 30/06 is longer than the 8mmm57, 308W, 7,7 Japanese etc.. meaning for the case former there is no shortage of longer cases.

Then there are fired cases from other chambers that you do not own, The long cases fired in other chambers is my second favorite. I have purchased fired cases from firing ranges, when picking through the brass I measure the length of the cases from the shoulder/datum to the head of the case. My best money is spent of long cases.

Long cases: My cases do not have head space and I do not own head space case gages, I own case length gages, I make comparators, when determining the length of a case I use a comparator. Seems complicated? Measure from zero or use a transfer or a standard, the head space gage is a standard and a transfer. Most of the cases I have purchased from a firing range will not chamber because they are too large in diameter and too long from the shoulder/datum to the head of the case.

Sizing a case to a chamber: For a reloader that knows nothing about forming can start by adjusting the die off the shell holder a known amount, there is nothing that beats the feeler gage when adjusting the die off the shell holder.
I would suggest .005" to start with. After sizing attempt chambering the sized case, if the case does not allow the bolt to close start with another case and reduce the gap to .003", if the .003" case will not chamber reduce the gap to .000", size another case then attempt chambering the case. If the case sized with no gap chambers with slight resistance to bolt closing measure the length of the case from the datum to the head of the case,

A case that will chamber with slight resistance to closing is being sized when the bolt is closed, a case that chambers without felt to resistance is shorter than the chamber from the shoulder of the chamber to the bolt face.

I measure the length of the chamber from the datum/shoulder to the bolt face, I start by forming cases that that allow the bolt to close, when adjusting the gap between the bottom of the die and top of the shell holder I use the chamber length from the shoulder/datum to the bolt face measurement when adjusting the die. For many rifles I can not miss it more than .004" if I do nothing but adjust the die to the shell holder, then there are those chambers that have excessive head space/length from the datum/shoulder to the bolt face.

 

[Terry O]

I've found it necessary to remove the primer with a separate die that doesn't change case size before determining actual shoulder length. This can also be done by running the depriming stem down on your FL die to get the primer out without changing the case. Slight primer set back and or cratering will impact your readings.

 

[rap36case]

I don't know what the concern is for headspace. I check with 2 headspace gauges and the meet spec. This weekend I was getting 2" 10 shot groups at 300yards with this process:

WW brass sorted first by weight, then by flyers (marked and discard)
de cap with pin and holder
clean with RCBS brush (uniform pocket and flash if new)
lube with wax
full length resize
expand with mandrel
trim to .001" of spec
expand again if needed (used cases get hard and springy)
turn to 0.012"
chamfer
clean with tissue to get out the wax lube
clean with corn cob
adjust neck to 0.331 (0.308 + 0.024 =0.332)
hand primer BR2
39.5g of IMR 4064
210SMK moly coated and corn cob polished
Seat to 2.220 base to ogive
check concentricity (less than 0.5 thousadths)

Rife: CZ550 varmint 'out of the box' with 6 to 24 50mm FFP PST