Measuring headspace

[yemtig]

Hi all.... I am a new reloader and want to reload for my rem700 cdl 30-06 for hunting rounds.... I have read tons of info on this site and others, have my reloading equipment, and have been saving my brass (mostly rem but some federal also) that has been fired from commercial ammo that I bought...

I am now in the process of brass workup and wanted to use my headspace guage which connects to my calipers to measure my headspace on my fire-formed brass....

Is it common to get a variance in measurements, because I am... The variance in measurements is not much, but is still there... Since my brass should match the dimensions of my rifles chamber, I would like to just bump the shoulder back .002-.003 with my fl die and load some rounds... How do I pick a headspace value to bump to with the variance? Maybe take a random sampling of 10-20 cases and go with the average and bump from there?? Just trying to do this right from the beginning and to get the most out of my reloads... Am I missing something??

Another thing that is confusing me is that my reloading manuals say that the headspace measurement should be 2.053 and on my fire-formed brass I'm getting values of 2.035-2.038

Why would my brass that is fire fitted to my chamber have a smaller headspace value than the published value in my reloading manual?

 

[Xcount]

Re: Measuring headspace

I don't have first hand knowledge of '.30 cal specifically but I think I can help.

First you mentioned different brands of brass and this will cause variations in brass after firing. even the same brand will give some variance, take the same brand and get an average, throw out the highest and lowest.

The SAAMII spec drawing I looked at showed 2.0587" as the max length and 2.0487 as the min. I could see your brass being 2.035 if your rifle was short chambered but factory brass would not have fit and closed the bolt. since the factory cartidge would have been around 2.0486 in order to fit inside the shortest chamber. I think you have mixed measurements or transposed a number because that is a dangerous difference between your fired brass and the SAAMII min. chamber spec. please double check.

To answer your questions:
1. take an average of a few of the same case and set back the shoulder .002 or if you want to guarantee feeding you can set back another thousand or so. if just works the brass more and reduces the life a little, your call. I set back semi auto brass around .005 and it lasts some 10 reloads. your call.


hope this helps.

 

[Fuzzball]

Re: Measuring headspace

Brass hardness varies within the same new box of 20, the springback will vary a tad when it's fired/expanded and again when it's squeeze/resized so there is no way we can get precisely the same head-to-shoulder lenght each time, nor is there any need to for most of us.

There is no point of setting the shoulder back at all in a bolt rifle, the fired case shoulders are ALL shorter than the chamber anyway.

It seems few guys realise it but the firing pin impact and primer explosion pushes most rimless cases a couple thou forward each time it's fired anyway so precise sizing is meaningless. And setting a shoulder back further than you need to simply accelerates case stretch for no good reason.

Forget about SAAMI specs, that's good for making guns but we have to live with what we git! For FL sizing all we really need to is <span style="text-decoration: underline">match the longest fired length to the longest resized case length</span>. Meaning forget averaging, all that would do is make about half your cases much shorter than they need to be.

 

[MitchAlsup]

Re: Measuring headspace

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: yemtig</div><div class="ubbcode-body">How do I pick a headspace value to bump to with the variance? </div></div>

If you are lucky, you will find a piece of brass that has just a bit of resistance as the bolt closes--this one is too long, but an accurate measurement of your chamber + bolt dimension. Measure it with your tool, write down the number.

Then set up your sizing die so that the brass comming out is 0.002 smaller than this number.

If you are unlucky, just continue to neck only size the cases until you run into a case that has expanded to the above criterion.

 

[SONIC SAAMI]

Re: Measuring headspace

You are over thinking all of this.
Find your longest piece of brass,set the die so it bumps the shoulder back .001.

Move on

 

[TexIndian]

Re: Measuring headspace

It's not unusual to get varying lengths. I'd find the longest one you have, make sure it will fit back into your chamber easily, and go with that as your chamber length. It usually takes several firings for a case to fully expand to fit the chamber. You might pick a couple of the longest cases, neck size only, and fire them again (trim if needed first). These should give you a better idea.

 

[Tripwire]

Re: Measuring headspace

Give the same dial caliper to 100 different reloaders and you'll likely get 100 different measurements. Dial calipers are NOT the end all precision instrument that common myth, and shooting forums, make them out to be. Which is why experienced reloaders pull their hair out when the newbies start posting questions like this.

That said, there is a common sense approach to getting consistent measurements with a dial caliper, and it involves developing a "knack" for using them. Woe to the new reloader who thinks a strong pressure put on the device will yield consistant results, he'll soon be making posts on a shooting forum asking why his brass varies in some dimension.

A high degree of finesse is required to just let the dial caliper stop "dead" for a "true" measurement that's conducive to the tolerance of the device, and even the best of the best dial calipers can be "forced" a few thousandths shorter. Especially extended out to the length of a .308 case.

Metal flexes under pressure, and dial calipers are made of metal.......

One trick to use when "measuring headspace" in the context here is to allow the caliper to stop dead, as I mentioned earlier, with only enough thumb pressure to keep it from backing up, and then slightly and carefully rotate the case just a little to work out any misalignment in the system. With only a slight thumb pressure, and if the case can be rotated just a little, and the dial will not read any shorter, then you have an "accurate" measurement. I bump an exact .001" with FL dies on precision loads, and I measure with a dedicated Starrett dial caliper, so it can be done.

At least some mechanical aptitude though, is required............

 

[gcoulsey]

Re: Measuring headspace

Welcome to the forum

+1 on what Tripwire just said,
Also, make sure you've deprimed the brass before using the headspace tool...
Sometimes the fired primers can be a little proud of the case which will throw your measurements off a few thou.

 

[Tripwire]

Re: Measuring headspace

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gfunkUK</div><div class="ubbcode-body">
Also, make sure you've deprimed the brass before using the headspace tool...
Sometimes the fired primers can be a little proud of the case which will throw your measurements off a few thou. </div></div>

Wow, can't believe that actually needs to be said.....no wait, yes I can believe it.

 

[yemtig]

Re: Measuring headspace

Thanks guys, guess I really am overthinking this whole process...

Here's what I'm gonna do....

Neck size my brass and focus on cranking out 20 rounds. Just focus on the basics and focus on being safe... I will refine this process as I work up my first load (180gr Sierra SBT) and then will see what works and what doesn't....

Baby steps.....