Headspace Comparitor & Bumping

[Regis G]

On my new 6BR, I decided to use a neck sizing & bump die. I finally got to use My Honrnady headspace comparator and was a little surprised to find some differences in cases that I had fired. Most measured 3.130 with some at 3.129 and few more at 3.135. Is that a normal spread?
Would bumping back to 3.120 make sense or is that way too much?

Appreciate any help.
Regis

 

[John Russell]

On my new 6BR, I decided to use a neck sizing & bump die. I finally got to use My Honrnady headspace comparator and was a little surprised to find some differences in cases that I had fired. Most measured 3.130 with some at 3.129 and few more at 3.135. Is that a normal spread?
Would bumping back to 3.120 make sense or is that way too much?

Appreciate any help.
Regis

Don't bump them unless they are making the bolt hard(er) to close.

Everytime you bump a case shoulder, whether it is 1 thou or 20 thou, you can add that number to the amount that the case stretches on the next firing.

 

[madmixerman]

On my new 6BR, I decided to use a neck sizing & bump die. I finally got to use My Honrnady headspace comparator and was a little surprised to find some differences in cases that I had fired. Most measured 3.130 with some at 3.129 and few more at 3.135. Is that a normal spread?
Would bumping back to 3.120 make sense or is that way too much?

Appreciate any help.
Regis

Did you remove the primers first? A little crater on a primer will give you different measurements.

 

[RonAKA]

On my new 6BR, I decided to use a neck sizing & bump die. I finally got to use My Honrnady headspace comparator and was a little surprised to find some differences in cases that I had fired. Most measured 3.130 with some at 3.129 and few more at 3.135. Is that a normal spread?
Would bumping back to 3.120 make sense or is that way too much?

A poster in another thread made a good suggestion, which I have not tried, but will try in your situation. The suggestion was to pop the primer from a fired case (the one that measured 3.135 would be a good one), and then partially reseat the primer again so it is sticking out half way or so. Chamber it, and close the bolt carefully. Now when you extract it take another measurement to see how much of the primer is still sticking out. That is an indication of how far your shoulder on the case may be from the shoulder in the chamber. It is quite possible your brass if just once fired may be still short of full expansion. A more reasonable bumping target would be to get within 0.002" of the shoulder in the chamber. That may mean some or even all of the cases still do not require bumping.

No, bumping back to 3.120" does not make any sense at all.

 

[fguffey]

On my new 6BR, I decided to use a neck sizing & bump die.

And then you went to the Hornady head space gage? My cases do not have head space and I am not sure what 6mmBR you are measuring. And then then there is maximum overall length, case length and the length of the case from the shoulder to the case head.

All of the measurments you have listed are longer than my 8mm Remington mag cases. The length of the 8mm Remington case from the shoulder to the case head is less than 2.50" and the length of the case is 2.850"; meaning your 6mm bench rest has to be the gorilla of 6MM bench resaters.

F. Guffey

 

[fguffey]

I decided to use a neck sizing & bump die.

bump die? Does your bump die have case body support? I find it impossible to bump a shoulder back with a die that has case body support; most reloaders have no clue what that means because there believe they can move the shoulder back.

F. Guffey

 

[Regis G]

Did you remove the primers first? A little crater on a primer will give you different measurements.

No, I did not.
Thank you will do.
Regis

 

[Regis G]

And then you went to the Hornady head space gage? My cases do not have head space and I am not sure what 6mmBR you are measuring. And then then there is maximum overall length, case length and the length of the case from the shoulder to the case head.

All of the measurments you have listed are longer than my 8mm Remington mag cases. The length of the 8mm Remington case from the shoulder to the case head is less than 2.50" and the length of the case is 2.850"; meaning your 6mm bench rest has to be the gorilla of 6MM bench resaters.

F. Guffey

FUNNY....LOL I zeroed without the comparator on.... Just ran back and zeroed with it on. Measured 1.124". So much for the gorilla 6BR.
Thanks for cheering me up today,
Regis

 

[Regis G]

bump die? Does your bump die have case body support? I find it impossible to bump a shoulder back with a die that has case body support; most reloaders have no clue what that means because there believe they can move the shoulder back.

F. Guffey

Well, I have a Forester. I do know what you mean but, did not think of that when deciding. I'll have to check it.
Thanks,
Regis

 

[LHSmith]

Find the "Bump" distance (as determined by your comparitor) that just allows your bolt (without FP spring) to just fall on it's own......."Bump" an extra 0.002" for non-comp. shooting and use that as your default setting. Note- keep in mind that brass -even from the same lot, fired the same number of times-with the same exact load will work harden at different rates. To overcome this, measure each piece with the comparator and using die shims adjust the degree of bump accordingly on those that are out of the target bump dimension/ or start annealing your brass. Setting the brass back the "proper" amount each time is a lot easier on the brass than only setting it back at hard bolt closure ...hence the reason I have standardized on FL sizing dies only, and my Neck sizers are a distant memory.

 

[LHSmith]

bump die? Does your bump die have case body support? I find it impossible to bump a shoulder back with a die that has case body support; most reloaders have no clue what that means because there believe they can move the shoulder back.

F. Guffey

Bump does happen....I have verified this a gazillion times. Your intentions may be well meaning but your posts do a huge disservice to the readers. Redding claims their dies bump, likewise Forster, and "bump" has been part of the language for years.

 

[LHSmith]

My cases do not have head space and I am not sure what 6mmBR you are measuring.


F. Guffey

From RCBS catalog "Full Length Die sets-Group A".........."This two die set is intended for reloading bottleneck cases..... the full length die brings the case to minimum SAAMI cartridge dimensions. Headspace is held to minimum tolerances to avoid changing the case body length during full length sizing." Lets not rewrite reloading vernacular that has been well established.

 

[M-61]

On my new 6BR, I decided to use a neck sizing & bump die. I finally got to use My Honrnady headspace comparator and was a little surprised to find some differences in cases that I had fired. Most measured 3.130 with some at 3.129 and few more at 3.135. Is that a normal spread?
Would bumping back to 3.120 make sense or is that way too much?

Appreciate any help.
Regis

Take a look at the numbers below. I don't think the numbers you have written above can be measured on a 6BR or I am missing something big time?
Then again I just read fguffy's answer and I'm more than a bit confused.


http://www.accurateshooter.com/cartridge-guides/6mmbr/

 

[LHSmith]

To take the "bump" meaning further....the number derived from a comparator is an arbitrary number, it in itself offers no value to others (chambers and comparator tools all vary)....what you are determining is a delta L -a difference in measured length from case head to shoulder to precisely find the die setting where shoulder set-back just occurs and then fine tune it for the desired clearance within your rifles chamber.

 

[Regis G]

Take a look at the numbers below. I don't think the numbers you have written above can be measured on a 6BR or I am missing something big time?
Then again I just read fguffy's answer and I'm more than a bit confused.


http://www.accurateshooter.com/cartridge-guides/6mmbr/

You're right of course. Measurements I gave were zeroed before I attached gauge. Actual when I re-checked & re-zeroed is 1.123"
Thanks,
Regis

 

[TimB]

One thing I became aware of recently is that all resizing dies of the same type (but different manufacturers) are NOT the same. For example, a Hornady bushing neck die will perform a shoulder bump. My RCBS and Redding bushing neck dies will not touch the shoulder or body. Therefore we should always ask which die someone is using.

In regard to headspace comparators, I have also found a difference between different manufacturers. My Hornady headspace measurement tool gives me a length of 1.6205 for fireformed 308 cartridges, whereas, my RCBS headspace tool gives me 1.629 for the same cartridges. The RCBS is designed to read at SAAMI minimum (1.630) when zeroed. I don't know which tool is giving me the most accurate measurement, but because I mainly use them for relative measurements, it really doesn't matter.

Tim

 

[TimP]

On my new 6BR, I decided to use a neck sizing & bump die. I finally got to use My Honrnady headspace comparator and was a little surprised to find some differences in cases that I had fired. Most measured 3.130 with some at 3.129 and few more at 3.135. Is that a normal spread?
Would bumping back to 3.120 make sense or is that way too much?

Appreciate any help.
Regis

How many times have you fired these cases. Once properly formed to your chamber they should all measure the same. There is no need to bump your shoulders until you have determined that dimension.
What works best for me is to take two or three cases to the range and neck size them with a standard neck sizing die until they have expanded to your chamber's dimensions. Measure them after each firing primer removed. This can be done during load development and checking for pressure signs. You can then set your bump die accordingly.

 

[RonAKA]

For what it is worth, I have the Forster Bushing Bump Die in 6BR, and recently bought the Hornady "headspace" gauge. I just used it to check some 1X fired and unsized cases, as well as some sized and reloaded 1X fired cases. I was setting the bump by using the Forster Bump die itself as a gauge, as I did not have the Hornady gauge when I reloaded these guys. I used the 0.350 bushing, and the offset from zero is 2.000". After subtracting the offset here is what I got when I just measured these cases:

1X fired unsized cases - 1.163" to 1.164"
1X Bumped and reloaded - 1.162"
5X fired and unsized cases 1.164" to 1.165"

Looking at your numbers, it would appear my chamber is about 0.040" longer than yours. The absolute number is not really a concern, unless you are loading for multiple guns. What you want to do is bump so the case is about 0.002" short of the chamber. The primer method is worth trying to see where you stand with respect to the chamber, and I have not done that. However the 5X fired case measurements would suggest they are not getting any bigger. Perhaps 0.001" off full growth.

Today was the first time I used the Horandy gauge. From what I can see, I will probably set the die next time to give me a shoulder of 1.164", which probably means that most of those 1X fired cases will not be bumped at all. Those 5X fired cases are waiting to be annealed, and will be bumped to 1.164" as well after annealing.

 

['Freak]

The feel (and visuals) of closing the bolt, stripped of its firing pin and ejector, on a fire formed and/or otherwise length manipulated case inside the chamber in question, is the best and only reliable way to find what reference number will be returned by whatever your favorite case measuring gadget once the said case’s head to shoulder datum length has reached the point of being right at completely filling the bolt face to shoulder datum length of that particular receiver, bolt, and chamber (barrel) assembly.

Record for all prosperity “the number”, what gadgets/instruments were used in arriving at “the number”, and never need to manipulate case head to shoulder datum length to test for fit only after stripping the bolt, just to find what’s representative of that chamber’s bolt face to chamber shoulder datum length all over again.

If new unfired brass checks on your gadget .006” shorter than “the number” then you’ll know it has .006” more lengthening to go before it’ll need any shoulder bump. If a case fired once or a couple or three or however many times and when using your gadget, etc., it measures a thousandth or so still shorter than “the number” which is same as the chamber’s length, then there’s still no need to bump back the case shoulder.

Once lengthened to the point that it does need a shoulder bump, I try to maintain ~ .001” to .002” less than the chamber’s length, same as ~ .001” to .002” less than “the number”, all from using my favored gadget.

 

[fguffey]

In regard to headspace comparators, I have also found a difference between different manufacturers. My Hornady headspace measurement tool gives me a length of 1.6205 for fireformed 308 cartridges, whereas, my RCBS headspace tool gives me 1.629 for the same cartridges. The RCBS is designed to read at SAAMI minimum (1.630) when zeroed. I don't know which tool is giving me the most accurate measurement, but because I mainly use them for relative measurements, it really doesn't matter.

Hornady/Sinclair does not have a head space gage that measures head space because the case does not have head space. And then from the beginning the Hornady/Sinclair tool has and has an inherent problem and the reloader has a problem. Both problems involve 'the datum'. Hornady datums have a radius, in the real world the datum does not have a radius. A radius on a datum turns the tool into a comparator. Problem: Forget using the Hornady tool for anything other than a comparator and it does not do well when comparing other measurements made with other tools. A reloader with shop skills and or a smith should be able to make tools to verify a gage, if a smith/reloader can make a tool to verify a tool they should be able to make the tool; that is what I once believed but now? Not so much.

Wilson makes a case gage; Wilson's case gage datum has a radius. Reloaders tried to sell other reloaders on the ideal the Wilson case gage was a drop-in gage for two reasons; they did not know how it was designed or they there trying to sell other rleoaders a different tool.

A real head space gage can be used to check the Horandy comparator. After verifying the tool the user can use the error for adjustment. I am the fan of measuring before, during and after. I am also the fan of being able to measure the length of the chamber from the shoulder to the bolt face; if a reloader/smith could measure the length of the chamber from the shoulder to the bolt face there would be no use for a tool that has error built into it.

I know, many reloaders purchase bushing from hardware stores for nickels and dimes; the bushings work if the reloader knows how to make them work.

F. Guffey

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