Headspace and full length sizing questions

[grumpygunner]

I have a couple technical questions about headspace and how to determine the correct dimensions when resizing my brass. I've tried to find this information both online and in my reloading book, but obviously I am not looking in the right place or I am completely misunderstanding something.

For context, I am reloading for a Bergara B14-HMR in 6.5 Creedmoor.

From my understanding, headspace refers to the distance between my rifles bolt face and the datum line in the chamber. Where the datum line is a ring located on the shoulder of the chamber with a diameter of 0.400 inches (for 6.5 Creedmoor according to SAAMI). Can someone confirm that my understanding of this is correct?

Can the term "headspace" refer to both the rifles chamber dimensions and a cartridge dimensions using the same measurement standards? If not, what is the proper term for this measurement when referring to the cartridge.

I was using a Lyman case gauge to resize my brass, believing that if the case fit between the gauges minimums and maximums that meant the case was resized properly, but a number of users on this forum corrected me and suggested I buy a proper headspace comparator. I have since purchased a Hornady Headspace Comparator Kit.

Now that I have the above mentioned comparator I can get accurate measurements of the case, but I did not have a way to measure my rifles headspace. To do so, I used the method Erik Cortina explained in this video.

I removed the firing pin and ejector from my bolt in order to allow the bolt to close freely when a properly resized cartridge is loaded into the rifle, as demonstrated in the video linked above. I then started slowly resizing a case until my rifles bolt was able to freely close with very little/no resistance. In order to make sure the case was not too small I put a thin piece of tape, approximately 0.002 inches thick, on the base of the resized case and the bolt did not close freely. Can anyone confirm that this procedure is appropriate?

Once I measured my fired and resized cases (base to datum line) I compared it to the SAAMI specs and this is one of the parts I really don't get.

All measurements are in inches.

SAAMI spec for the chamber: minimum1.541 / maximum 1.551
SAAMI spec for the cartridge: minimum 1.537 / maximum 1.544

Resized case: 1.534 (Cases larger than this do not allow me to close the bolt without moderate to significant resistance.)
Fired case: 1.540 +-0.001 (Average of 5 fired cases.)

And just as a sanity check I measured a number of factory rounds I had on hand (5 each).

Format: minimum, average, maximum

Hornady Match 140grn ELD-M
1.529, 1.531, 1.532

Sellier & Bellot Tactical 140grm FMJ
1.530, 1.531, 1.532

Federal American Eagle 123grn OTM
1.531, 1.532, 1.533

Can someone explain the following?

1. Why is my rifles apparent headspace far smaller than the SAAMI minimum?

2. Why is the fired case so much larger than the largest resized case I was able to easily fit in the rifle? I assume this is because the brass expands when fired, hence the need to resize, but that much of an increase seems excessive.

3. Why is the factory ammunition so far below the SAAMI specs?

4. Is there some slop in the SAAMI specs?

5. Am I getting too hung up the SAAMI specs?

6. Should I take my rifle to my local gunsmith to have him confirm that my rifles headspace is safe? I have already shot hundreds of rounds through my rifle without any incident, signs of overpressure or damage to the spent brass, so I assume this isn't necessary. If the headspace I measured was much larger than the SAAMI spec, I assume that would be cause for concern.

If there is anything else I appear to be misunderstanding or completely out to lunch on, please let me know.

Thanks

 

[Kracken McGraw]

I don’t think the bolt resistance deal works in all actions like your doing. I tried this on one rifle and I had to keep screwing the die down more and more and knew I was getting way too much cam over on my press to get where I was going. My opinion is to listen to your fired brass and bump it back a couple of thousandants.

 

[KRP]

1. You're not using the correct tool to measure headspace in the rifle. Measure a go gauge with your comparator, I would bet it doesn't measure 1.541. You're likely not measuring at exactly the .400 point because the tool is oversized or has a chamfer at the edge. It doesn't matter though as it will still give you comparative measurements to work with.

2. Yes, the brass expands when fired. The shoulder is not the only part of the case that can cause resistance to chambering.

3. Again, wrong tool for measuring this.

4. Yes, that's why there is a minimum and maximum. SAAMI standards are also voluntary.

5. Yes, in my opinion.

6. If it makes you feel better, take it to a gunsmith or get a set of headspace gauges check it. Your cases are growing less than the .014 allowed by a minumum cartridge in a maximum chamber per SAAMI dimensions though.

 

[59FLH]

KRP, is spot on, you process and understanding is good. The only thing your missing is the Hornady tool does not measure chamber size, it compares brass before and after sizing. Go with the bolt drop method for sizing, and get a HS gauge for chamber measurement,

 

[Coyotefurharvester]

3. Factory ammo, new brass must fit in all saami chambers of same cartridge. So it is on minimum side.
If your fired brass will chamber with low effort, use the comparator to set the die so brass is the same measurement to -0.001 less after sizing. I remove spent primers BEFORE comparator measurement, universal decap die. If you are using the decap/expander make sure the necks are lubed in/out, as the expander can pull the shoulder after case body/shoulder was sized.
It would be pure luck if your comparator body, go no go, chamber, all matched up including what the error and accuracy of your calipers.

 

[6BRA]

Calipers are inconsistent, spend the money on a instant indicator dial guage. Redding.

 

[DocCarbon]

I'll only add some Dies do a better job resizing than others do . Meaning brand new case gauge in a particular brand and their Dies Brand New ,DIDN'T jive as FL sized wouldn't go in their gauge .

As anyone who reloads knows or should know ,a precise ( Not some Harbor Junk ) Vernier caliper and even a Micrometer is a Must have . I own a Mahr and a Mitutoyo and they jive with each other . Brown & Sharpe USA made Mic set , their OLD .

As was previously posted New Ammo is slightly undersized ,so as too fit in any chamber . Ever hear of Small Based Dies for Semi Auto ,there's a REASON why they make them as not all chambers are equal .

 

[Dusty Stevens]

I'll only add some Dies do a better job resizing than others do . Meaning brand new case gauge in a particular brand and their Dies Brand New ,DIDN'T jive as FL sized wouldn't go in their gauge .

As anyone who reloads knows or should know ,a precise ( Not some Harbor Junk ) Vernier caliper and even a Micrometer is a Must have . I own a Mahr and a Mitutoyo and they jive with each other . Brown & Sharpe USA made Mic set , their OLD .

As was previously posted New Ammo is slightly undersized ,so as too fit in any chamber . Ever hear of Small Based Dies for Semi Auto ,there's a REASON why they make them as not all chambers are equal .

I dont agree with the vernier caliper. Theres a reason we dont use slide rules anymore. I do agree with the brand names in a dial caliper and a mic that reads tenths (along with a mid range certified standard to check the calibration

 

[miningshawn]

Am I the only fella using Hornady Lock-N-Load Headspace Comparators?

Hornady Lock-N-Load Headspace Ga 5 Bushing Set Comparator

The Hornady Lock-N-Load Headspace Gauge is a great tool for increasing the accuracy of your loaded ammunition. The Headspace gauge measures from the...

www.midwayusa.com

LOCK-N-LOAD™ HEADSPACE GAUGE TOOL | Brownells

The Lock-N-Load® Headspace Comparator extends brass life, improves accuracy, and enhances safety. The gauge measures variations in brass before and after firing or re-sizing. It allows for headspace comparison between fire-formed brass and re-size...

www.brownells.com

I even use a (GASP!) digital caliper. Measure fired cases, average headspace fired, set die to consistent -0.002" size, pull handle many times.

 

[DocCarbon]

Am I the only fella using Hornady Lock-N-Load Headspace Comparators?

Hornady Lock-N-Load Headspace Ga 5 Bushing Set Comparator

The Hornady Lock-N-Load Headspace Gauge is a great tool for increasing the accuracy of your loaded ammunition. The Headspace gauge measures from the...

www.midwayusa.com

LOCK-N-LOAD™ HEADSPACE GAUGE TOOL | Brownells

The Lock-N-Load® Headspace Comparator extends brass life, improves accuracy, and enhances safety. The gauge measures variations in brass before and after firing or re-sizing. It allows for headspace comparison between fire-formed brass and re-size...

www.brownells.com

I even use a (GASP!) digital caliper. Measure fired cases, average headspace fired, set die to consistent -0.002" size, pull handle many times.

NO you're not the only one as I also use one . MY mistake I should have stated Dial and Digital calipers ,as that's what I use . Correct tools wrong terminology MY bad .

Kind of like digital scales ,yes I've got extreme ones but DON'T use them other than to check manual scales .
MY powder anvils are very precise ,once set they don't vary a 1/10 Th. Gr. ,which is close enough for ME .

 

[LCazador]

I have a couple technical questions about headspace and how to determine the correct dimensions when resizing my brass. I've tried to find this information both online and in my reloading book, but obviously I am not looking in the right place or I am completely misunderstanding something.

For context, I am reloading for a Bergara B14-HMR in 6.5 Creedmoor.

From my understanding, headspace refers to the distance between my rifles bolt face and the datum line in the chamber. Where the datum line is a ring located on the shoulder of the chamber with a diameter of 0.400 inches (for 6.5 Creedmoor according to SAAMI). Can someone confirm that my understanding of this is correct?

Can the term "headspace" refer to both the rifles chamber dimensions and a cartridge dimensions using the same measurement standards? If not, what is the proper term for this measurement when referring to the cartridge.

I was using a Lyman case gauge to resize my brass, believing that if the case fit between the gauges minimums and maximums that meant the case was resized properly, but a number of users on this forum corrected me and suggested I buy a proper headspace comparator. I have since purchased a Hornady Headspace Comparator Kit.

Now that I have the above mentioned comparator I can get accurate measurements of the case, but I did not have a way to measure my rifles headspace. To do so, I used the method Erik Cortina explained in this video.

I removed the firing pin and ejector from my bolt in order to allow the bolt to close freely when a properly resized cartridge is loaded into the rifle, as demonstrated in the video linked above. I then started slowly resizing a case until my rifles bolt was able to freely close with very little/no resistance. In order to make sure the case was not too small I put a thin piece of tape, approximately 0.002 inches thick, on the base of the resized case and the bolt did not close freely. Can anyone confirm that this procedure is appropriate?

Once I measured my fired and resized cases (base to datum line) I compared it to the SAAMI specs and this is one of the parts I really don't get.

All measurements are in inches.

SAAMI spec for the chamber: minimum1.541 / maximum 1.551
SAAMI spec for the cartridge: minimum 1.537 / maximum 1.544

Resized case: 1.534 (Cases larger than this do not allow me to close the bolt without moderate to significant resistance.)
Fired case: 1.540 +-0.001 (Average of 5 fired cases.)

And just as a sanity check I measured a number of factory rounds I had on hand (5 each).

Format: minimum, average, maximum

Hornady Match 140grn ELD-M
1.529, 1.531, 1.532

Sellier & Bellot Tactical 140grm FMJ
1.530, 1.531, 1.532

Federal American Eagle 123grn OTM
1.531, 1.532, 1.533

Can someone explain the following?

1. Why is my rifles apparent headspace far smaller than the SAAMI minimum?

2. Why is the fired case so much larger than the largest resized case I was able to easily fit in the rifle? I assume this is because the brass expands when fired, hence the need to resize, but that much of an increase seems excessive.

3. Why is the factory ammunition so far below the SAAMI specs?

4. Is there some slop in the SAAMI specs?

5. Am I getting too hung up the SAAMI specs?

6. Should I take my rifle to my local gunsmith to have him confirm that my rifles headspace is safe? I have already shot hundreds of rounds through my rifle without any incident, signs of overpressure or damage to the spent brass, so I assume this isn't necessary. If the headspace I measured was much larger than the SAAMI spec, I assume that would be cause for concern.

If there is anything else I appear to be misunderstanding or completely out to lunch on, please let me know.

Thanks

Headspace is exactly what the word indicates. It is the space between the bolt face and cartridge head. Your cartridge measures 1.540 after firing and Sammi min. measure is 1.541. One thousand shorter is not significant in a world of factory rifles and who knows how accurately the Hornady guage is measureing. Bump your shoulders .002" and be done with it. Factory ammo is made smaller so it will fit in all rifles and so is virgin brass and yes it's possible to see as much as .010" less! This is why you should do any fireforming with a moderate load and jam the bullet into the rifleing so it will hold the cartridge to the bolt face for a good fireform. If you're using factory empties it's always a good idea to do a second fireform.

 

[Gargoyle]

.

 

[Titan]

Regarding question #2 are you measuring fired cases without removing the primer? This will lead to false measurements a fired primer can sit proud of the case.

 

[Laurie]

One thousand shorter is not significant in a world of factory rifles and who knows how accurately the Hornady guage is measureing.

Just to add to that, many of the problems and issues like those that arise on this thread are due to the tool being misleadingly / inaccurately named as a 'Headspace Gauge'. It is NOT a headspace gauge as several people have pointed out in their posts - it's a case shoulder position comparator - no more, no less. A very useful device, but purely for determining sizer die settings to obtain the correct amount of shoulder bump purely for one rifle's chamber. It can have a secondary use in measuring new brass out of the box to allow comparison with fired examples - that's how I discovered that Lapua 6.5mm Grendel brass shoulders are 0.009-0.010" 'short' of an ideal setting for my rifle, which starts to be a 'headspace issue', and sees me treat first use as a 'fireform job' loaded to put the bullet in the lands.

 

[LCazador]

Just to add to that, many of the problems and issues like those that arise on this thread are due to the tool being misleadingly / inaccurately named as a 'Headspace Gauge'. It is NOT a headspace gauge as several people have pointed out in their posts - it's a case shoulder position comparator - no more, no less. A very useful device, but purely for determining sizer die settings to obtain the correct amount of shoulder bump purely for one rifle's chamber. It can have a secondary use in measuring new brass out of the box to allow comparison with fired examples - that's how I discovered that Lapua 6.5mm Grendel brass shoulders are 0.009-0.010" 'short' of an ideal setting for my rifle, which starts to be a 'headspace issue', and sees me treat first use as a 'fireform job' loaded to put the bullet in the lands.

To add to what Laurie says. I use a barrel stub for measuring bump as well as bullet seating depth made with my reamer. A true representation of my chamber. If you shoot a custom barrel just one of the advantages!

 

[Ray123]

Nope...the chamber gauge is not perfect but close. The go gauge is what I cut all my chambers to...so the area or "line" half way between go and no go ..will not fit, any rifle I chamber for. It has to be on the low ledgeof the chamber gauge, which may not be accurate.
So I use the go gauge I chambered the rifle with...drop the go gauge into the Wilson case gauge. On a surface plate with a drop indicator, I check the min of what the gauges says with the actual go gauge used to chamber the rifle. With the go-gauge inserted into the chamber gauge, the dial indicator on the surface plate will so how far off your gauge is with respect to your chamber. Your bolt should close on the go-gauge, for your specific cartridge. But wildcats and my 6 dasher are a combination of Alpha dasher brass and a dasher go gauge, for a very close fit. So half way up the case gauge, would be .003 too long for my chamber.