Shoulder bump inconsistency

[Max_The_Phoenix]

Hi everyone
Just started reloading 2 months ago
Running into a interesting question:
I was measuring all my brasses that fired once in my 6.5cm bolt gun and seeing different headspace vary from 1.555 to 1.560. Out of those 77 brasses, 26 of them are 1.558 and about 15 of them 1.557
My question is
1-which one should I select to adjust my die to push shoulder back by 0.002?

Should I select 1.557 so all the cases become 1.555?

I already measured the c.b.t.o based on sized brass that has 1.558

2- should i do another measurement based on the longest case or shortest case?

Thanks

 

[DeathBeforeDismount]

Could be alot of things.

1. First is you and or measuring device. If you don't have good tools ( calipers and gages, hornady is junk) and know how to use precision measuring devices you will get inconsistent readings. Google this and yoube some stuff, and get some SAC comparitors to eliminate this variable

2. Press stroke. If you aren't doing the exact same sizing stroke to either cam over or bottom out die, you will get inconsistent bump.

3. Annealing with a real machine that actually anneals not just hits with a flame. This will effect sizing and springback.

4. Lube. Getting rid of outdated shitty lube practices and going to lanolin/alch will solve this problem.

This is all assuming you have good, consistent brass and a bushing fl sizing die.

 

[FredHammer]

Pushing the shoulder back .002 is an arbitrary distance picked to allow for a clear chambering of the round. A clean chamber and case with a shoulder .005 from front of chamber will close smoothly, with a bit of touch. .001 away from chamber shoulder area is a free & clear chambering.

.002 adds space for dirty chamber, some slop in shoulder bumping, and insurance for reliability. Some people don’t do .002, but instead have the case shoulder contacting the chamber. Under the notion it’s more better. Also consider the spring back of the brass can be .0005-.001 so the brass shrinks a bit to release from the chamber walls. You’re .002 might really be .0025-.003 away in actuality.

Putting this into perspective, factory brass of loaded ammo, and new brass sold as components have shoulders that initially measure generally .015 from the chamber shoulder wall. That’s a big ole jump/stretch of the case and matches have been won, ragged hole groups been had. Federal Gold Medal Match, for example.

With all that said, just make sure the round chambers smoothly/freely. Go shorter than longer if you are on the fence. I try to stay .002-.003 from fired brass shoulder length. I recently switched to a cam over press, RCBS Summit after 25yrs of a non cam over press and the ease of hitting that .002 consistency drastically increased. However, I still need to apply same pressure/stroke style right at the cam over point.

 

[Max_The_Phoenix]

Pushing the shoulder back .002 is an arbitrary distance picked to allow for a clear chambering of the round. A clean chamber and case with a shoulder .005 from front of chamber will close smoothly, with a bit of touch. .001 away from chamber shoulder area is a free & clear chambering.

.002 adds space for dirty chamber, some slop in shoulder bumping, and insurance for reliability. Some people don’t do .002, but instead have the case shoulder contacting the chamber. Under the notion it’s more better. Also consider the spring back of the brass can be .0005-.001 so the brass shrinks a bit to release from the chamber walls. You’re .002 might really be .0025-.003 away in actuality.

Putting this into perspective, factory brass of loaded ammo, and new brass sold as components have shoulders that initially measure generally .015 from the chamber shoulder wall. That’s a big ole jump/stretch of the case and matches have been won, ragged hole groups been had. Federal Gold Medal Match, for example.

With all that said, just make sure the round chambers smoothly/freely. Go shorter than longer if you are on the fence. I try to stay .002-.003 from fired brass shoulder length. I recently switched to a cam over press, RCBS Summit after 25yrs of a non cam over press and the ease of hitting that .002 consistency drastically increased. However, I still need to apply same pressure/stroke style right at the cam over point.

I am using the co-ax press with hornady match grade bushings die and I can get exactly .002 shoulder bump
But tge thing is the cases came out the rifle with different shoulder sizes therefore if I size the one that came out of rifle as 1.558 will be 1.556 and the others equal or shorter than 1.556 won’t be bumped at all!

So after first firing cycle which size should be my reference to adjust my die to begin with?
The caee with longer shoulder or the shortest one?
Please help me figure this part out cause I’m very confused

 

[nn8734]

I am using the co-ax press with hornady match grade bushings die and I can get exactly .002 shoulder bump
But tge thing is the cases came out the rifle with different shoulder sizes therefore if I size the one that came out of rifle as 1.558 will be 1.556 and the others equal or shorter than 1.556 won’t be bumped at all!

So after first firing cycle which size should be my reference to adjust my die to begin with?
The caee with longer shoulder or the shortest one?
Please help me figure this part out cause I’m very confused

Was this rifle built for you? If so, do you have a chamber diagram or reamer print for the reamer used to cut the rifle’s chamber? If so, that will give you the dimensions you need to set up your sizing die.

What tool are you using to measure case head-shoulder datum of your fired cases?

 

[spife7980]

Hi everyone
Just started reloading 2 months ago
Running into a interesting question:
I was measuring all my brasses that fired once in my 6.5cm bolt gun and seeing different headspace vary from 1.555 to 1.560. Out of those 77 brasses, 26 of them are 1.558 and about 15 of them 1.557
My question is
1-which one should I select to adjust my die to push shoulder back by 0.002?

Should I select 1.557 so all the cases become 1.555?

I already measured the c.b.t.o based on sized brass that has 1.558

2- should i do another measurement based on the longest case or shortest case?

Thanks

Watch the video called sizing brass. If you size the 1.560 back to 1.558 does the bolt stripped of firing pin and spring ejector chamber the case easily? What about when you size it to 1.557 etc.
Use your chamber to be the final determinator.

Videos | wheeleraccuracy

www.wheeleraccuracy.com

 

[Hickswr]

Are the brass all the same manufacturer?

 

[Mudflap621]

If those are your fired measurements I’m assuming they probably aren’t done growing yet. Strip your bolt of firing pin and ejector and if the bolt drops free without resistance than you don’t need to bump shoulders just yet.

 

[Max_The_Phoenix]

Was this rifle built for you? If so, do you have a chamber diagram or reamer print for the reamer used to cut the rifle’s chamber? If so, that will give you the dimensions you need to set up your sizing die.

What tool are you using to measure case head-shoulder datum of your fired cases?

Yes Altus shooting built this rifle for me.
Barrel is proof carbon, I think they told me they chambered it from from blank.
I think I can ask them to send me the digram.

So if i got it right, I have to measure my jam point based on the sized case that’s been bumped .002 from chamber’s shoulder measurement?

Using hornady headspace comparator
Placed an order for SAC yesterday.

Thanks for the idea

 

[Max_The_Phoenix]

Are the brass all the same manufacturer?

Yes

If those are your fired measurements I’m assuming they probably aren’t done growing yet. Strip your bolt of firing pin and ejector and if the bolt drops free without resistance than you don’t need to bump shoulders just yet.

Will try that one thanks

 

[nn8734]

Yes Altus shooting built this rifle for me.
Barrel is proof carbon, I think they told me they chambered it from from blank.
I think I can ask them to send me the digram.

Using hornady headspace comparator
Placed an order for SAC yesterday.

Thanks for the idea

The diagram will remove all the ambiguity associated with setting up your die. Always get a reamer print from your rifle builder for all rifles built for you.

 

[Max_The_Phoenix]

The diagram will remove all the ambiguity associated with setting up your die. Always get a reamer print from your rifle builder for all rifles built for you.

Just talked to them, they told me its saami spec, so if it’s saami, there is a big difference from my shortest fired shoulder which is 1.555 to saami 1.5438
unfortunately i have no time to go to range to test the accuracy again, cause they told me if it doesn’t shoot 3/8 with factory ammo you need to send it

 

[nn8734]

Just talked to them, they told me its saami spec, so if it’s saami, there is a big difference from my shortest fired shoulder which is 1.555 to saami 1.5438
unfortunately i have no time to go to range to test the accuracy again, cause they told me if it doesn’t shoot 3/8 with factory ammo you need to send it

Your measurements are all over the place. Something’s wrong with either your tool, how its set up or how you’re using it.

Here’s saami spec headspace range for a 6.5 creedmoor


I use these gauges to set up my fl sizing dies for .308 and 6.5CM. For other cartridges, ill use the reamer diagram to start and adjust from there.

Ask for the drawing...

 

[Max_The_Phoenix]

Your measurements are all over the place. Something’s wrong with either your tool, how its set up or how you’re using it.

Here’s saami spec headspace range for a 6.5 creedmoor
View attachment 8107986

I use these gauges to set up my fl sizing dies for .308 and 6.5CM. For other cartridges, ill use the reamer diagram to start and adjust from there.

Thanks a lot man
I will order one if these now

 

[nn8734]

Thanks a lot man
I will order one if these now

Check ebay or amazon...to be honest, not sure how available they are as I have had them for years...otherwise, just get the reamer print.

Meanwhile, id figure out why your brass seems to vary so much; i can't believe its the brass itself if you seeing that much of a difference in your measurements...measure each case at two or three points by rotating it in the Hornady comparator bushing...I see one to two thou difference from time to time, especially if brass was brand new before I fired it.

 

[Max_The_Phoenix]

Check ebay or amazon...to be honest, not sure how available they are as I have had them for years...otherwise, just get the reamer print.

Meanwhile, id figure out why your brass seems to vary so much; i can't believe its the brass itself if you seeing that much of a difference in your measurements...measure each case at two or three points by rotating it in the Hornady comparator bushing...I see one to two thou difference from time to time, especially if brass was brand new before I fired it.

Yes I always rotate it in the bushing to measure. I hope it’s not a gunsmithing issue since I don’t have time to go check the accuracy
First time I went to range was trying yo break in the barrel and just fire form the brass. Let’s see
Thank you for helping me since it’s my first custom rifle and very new to reloading

 

[nn8734]

Yes I always rotate it in the bushing to measure. I hope it’s not a gunsmithing issue since I don’t have time to go check the accuracy
First time I went to range was trying yo break in the barrel and just fire form the brass. Let’s see
Thank you for helping me since it’s my first custom rifle and very new to reloading

You’re welcome and agree, hope it doesn’t have to go back as that’s always a pain in the ass.

 

[supercorndogs]

Chamber the brass you have, find some that are tight, bump those shoulders until they fit. It really doesn't have to be this complicated.

If none of them are tight, set up your FL die to only neck size them and shoot them again.

Lower pressure loads may not blow the brass out all the way in one firing.

 

[supercorndogs]

Your measurements are all over the place. Something’s wrong with either your tool, how its set up or how you’re using it.

Here’s saami spec headspace range for a 6.5 creedmoor
View attachment 8107986

I use these gauges to set up my fl sizing dies for .308 and 6.5CM. For other cartridges, ill use the reamer diagram to start and adjust from there.

Ask for the drawing...

Are you saying, you screw your die down on a headspace gauge to get a starting point?

How do use a reamer diagram to set up a die?

What does the drawing tell us measuring brass doesn't?

 

[nn8734]

Are you saying, you screw your die down on a headspace gauge to get a starting point?

How do use a reamer diagram to set up a die?

What does the drawing tell us measuring brass doesn't?

Lol, fuck no.

I start inserting gauges into the rifle until i get one that fits cleanly, starting with the longest. Then I set that gauge in the comparator, zero the indicator then stick a piece of brass in the press.

Size, measure, adjust until the indicator shows -.002.

Reamer print: i size a piece of brass until it matches the reamer print dimensions then adjust until i get -.002.

I then test fit to ensure bolt closes cleanly.

If i have neither reamer print nor headspace gauge, i rely on fired brass from factory ammo or a handload with a nominal charge weight. Most of the time, fired brass works (my measurements are all within .002 or so, not all over the map like the OPs).

Ill put pics using the gauge if the above explanation isn’t sufficient.

 

[supercorndogs]

I don't understand the advantage of using arbitrary measurements from headspace gauges and reamer prints, rather than measuring brass from the rifle. Neither a headspace gauge nor a reamer print can tell you what the brass can.

 

[nn8734]

Then don’t worry about it. You do what works for you and ill do what works for me.

The OP’s problem is he’s not getting consistent measurements so he needs to figure out why before going any further.

 

[spife7980]

Or he is and his brass just isnt all fully formed.

 

[nn8734]

Unless his numbers are mistated, i doubt it. but anything’s possible.

I use headspace gauges so I don’t have to worry about non fully formed brass preventing me from getting reliable reference measurements. I start with a gauge or blueprint and go from there.

But again, you and corn dog can take whichever approach you want and works for you.

 

[Mudflap621]

Unless his numbers are mistated, i doubt it. but anything’s possible.

I use headspace gauges so I don’t have to worry about non fully formed brass preventing me from getting reliable reference measurements. I start with a gauge or blueprint and go from there.

But again, you and corn dog can take whichever approach you want and works for you.

No offense but just because you have a blueprint doesn’t mean the chamber is exactly the same.

I typically see different measurements on virgin fired brass that hasn’t been fully formed to the chamber.

I just measured a bunch of fireformed BRA last night that’s got a spread of almost .002” and all but the longest drop free on a stripped bolt. Needless to say I won’t be setting any shoulders back u til the next firing.

Strip the bolt and test the brass in the chamber, no print or store bought chamber gauge is going to help.

 

[DeathBeforeDismount]

This is why alot of better shooters are doing more than a .002 bump. Closer to .003 or .0035. It works the brass harder but ensures feeding.

 

[nn8734]

No offense but just because you have a blueprint doesn’t mean the chamber is exactly the same.

I typically see different measurements on virgin fired brass that hasn’t been fully formed to the chamber.

I just measured a bunch of fireformed BRA last night that’s got a spread of almost .002” and all but the longest drop free on a stripped bolt. Needless to say I won’t be setting any shoulders back u til the next firing.

Strip the bolt and test the brass in the chamber, no print or store bought chamber gauge is going to help.

None taken.

If it varies, it’s not going to be more than a couple thou unless it was not cut to match the blueprint (which is always possible). Ive always received a blueprint and fired brass has always been within one or two thousandths. But in absence of consistent measurements on fired brass, the blueprint gives the loader another place to start while he figures out what’s goikg on with the measurements. The op’s problem is lack of consistency when measuring fired brass so having another reference point would help at least in the short term. Regardless of reason whether its due to brass not fully formed, (often takes a couple firings to fully fireform) or because his measurements, method or tools are off or some other reason, he needs to figure that out (as I’ve already said like three times now).

The Chamber gauges (store bought or otherwise) are machined to saami in .001 increments for the saami range for the carteidge so I don’t see why they wouldn’t be appropriate to use and have never had a problem using them to determine headspace and/or set up a die. Whether or not they’re worth the price is up to the individual.

 

[Marine52]

Unless his numbers are mistated, i doubt it. but anything’s possible.

I use headspace gauges so I don’t have to worry about non fully formed brass preventing me from getting reliable reference measurements. I start with a gauge or blueprint and go from there.

But again, you and corn dog can take whichever approach you want and works for you.

I like nn8734‘s approach and I have a similar method. The Forster HS gauge set is nice but Forster stopped making them. I use a go gauge and then use aluminum foil on end with a smidge of paste to find exact headspace (reg foil is about .0004 - .0006” and ” and heavy foil is right at .0008”). I do this on a newly chambered barrel and then I have a set target number for the rest of its life. If I want .002 bump, all I do is index off of the go gauge. I will confirm case fit in chamber for early sizing.

regarding the use of a reamer print, I believe all such prints just show the SAAMI HS range Min to max. This is because the gunsmith sets the actual HS with a go-gauge and normally does it at SAAMI min but the customer can specify.

 

[FLIGHT762]

Just talked to them, they told me its saami spec, so if it’s saami, there is a big difference from my shortest fired shoulder which is 1.555 to saami 1.5438
unfortunately i have no time to go to range to test the accuracy again, cause they told me if it doesn’t shoot 3/8 with factory ammo you need to send it

O/P, you are NOT going to get a SAAMI headspace reading off of your Hornady Comparator. It is a Comparator, NOT a headspace gauge. New reloaders think you'll get SAAMI numbers off of the comparator, you do not. Just use the numbers you get off of you fired brass and set the die to bump minus .002"-.003" off of that measurement reading. There's nothing wrong with your Comparator. You do need to decap primers before taking a measurement because primers can crater and give false readings.

 

[Max_The_Phoenix]

O/P, you are NOT going to get a SAAMI headspace reading off of your Hornady Comparator. It is a Comparator, NOT a headspace gauge. New reloaders think you'll get SAAMI numbers off of the comparator, you do not. Just use the numbers you get off of you fired brass and set the die to bump minus .002"-.003" off of that measurement reading. There's nothing wrong with your Comparator. You do need to decap primers before taking a measurement because primers can crater and give false readings.

Yes I always deprime and tumble before any measurements

 

[Holliday]

I’m shooting 280 Ackley with 40° shoulder. I was having a heck of a time with inconsistent setback. It’s my opinion the 40° shoulder exacerbates the problem.

First I switched to the SAC comparators. The Hornady are crap. https://shortactioncustoms.com/product-category/headspace-comparators/

You need a decent caliper. I use Mitutoyo.

https://www.mscdirect.com/product/details/62529482

careful where you buy due to Chinese knockoffs

Then I switched to Alpha Brass’s case lube: https://alphamunitions.com/product/alpha-case-sizing-lube/

I anneal every 3rd firing.

 

[Max_The_Phoenix]

I’m shooting 280 Ackley with 40° shoulder. I was having a heck of a time with inconsistent setback. It’s my opinion the 40° shoulder exacerbates the problem.

First I switched to the SAC comparators. The Hornady are crap. https://shortactioncustoms.com/product-category/headspace-comparators/

You need a decent caliper. I use Mitutoyo.

https://www.mscdirect.com/product/details/62529482

careful where you buy due to Chinese knockoffs

Then I switched to Alpha Brass’s case lube: https://alphamunitions.com/product/alpha-case-sizing-lube/

I anneal every 3rd firing.

Thanks SAC will be in tomorrow
Will use Peterson brass for load development
Been using mitutoyo for years they are the best imo

 

[Holliday]

I personally only push back .001 to .0015”. I never have any issues with feeding. And my 280 AI is my hunting rifle.

 

[Wile_Coyote]

Measurements may be bouncing around because it is only once fired brass.

I just shot a couple boxes of new Norma in my 6.5 PRC, so new brass to form to my chamber (factory rifle so no drawing). Measuring as 1x fired resulted in the range 1.6450-1.6460.

I measured a lot of Norma that has been fired 4x from my rifle. All were consistently 1.6460.

I then checked some 1x fired Nosler brass from my rifle. Results were the same as the Norma 1x fired, 1.6450-1.6460.

I will use that 1.6460 to bump back 0.002.

I didnt see who manufacturer your brass was, but may be playing into things. 1x fired as stated hasn't finished fully forming. I dont know if that happens on the second, third... firings, but my 4x were all holding very consistent. Manufacturers use different alloys so it probably comes into play.

I have 100 new Peterson cases to move to when my factory brass is retired. It'll be interesting to see how that works in comparison to the Norma and Nosler.

 

[tho98027]

Sounds like a lube issue. The right amount on some brass and not enough on others. On a side note, OP, if you are using quality brass like lapua, alpha, or peterson, I would aim for 3-4 thousands shoulder bump. Its never affected the life of the brass with good brass. If hornady brass than just 2 thousands bump or eventually you could seperate a head. I've bumped shoulders from 0.5-1 thousands all the way to 4. Loosy goosy has always worked better for accuracy. .02 Flame on.

 

[bax]

OP said that his once-fired brass measured 1.555 to 1.560. He says that he can pick a number (for example 1.557) in that range and reliably resize to -.002 or 1.555. Since his once-fired brass is coming out different lengths, he is asking what number in that range to use.

People said ...

his once-fired brass is all the same size but he can't measure well.
he is using bad measurement tools.
he should use a chamber print to set up his sizing die
he should use a headspace gauge to set up his sizing die
Variation is real but caused by lube
He has poor quality brass and it comes out of the chamber different sizes
He can't use Hornady comparators and a print to set anything
uniform press stroke is important
He need to properly anneal his brass
OP is right, the brass measurements are really different and it is still growing

OP said that this is once-fired brass. The brass has not been sized yet so lube, press stroke, and annealing don't count - yet.

Comments about using a chamber print or headspace gauge may be useful after he picks a number but he still needs to set the die up using chamber size, not the print. If you have a headspace gauge and it fits the chamber, you can use it to get a starting point for the sizing die.

Based on reading OP's comments, I believe that he is using his existing tools correctly and that the tools are giving him consistent results. It remains to be seen how good the brass is. Based on that belief and my experience, I believe that the brass is still growing - once-fired doesn't always stretch it out.

The whole point of the minus two thou setting is to insure reliable feeding without heavy bolt close and to provide some room for crud. And the minus 2 thou number depends on the actual chamber size. It doesn't depend on the print. I find chamber size this way:

First find a case that is chamber size. Strip the firing pin and ejector from the bolt, take each piece of fired brass and try to chamber it. When chambering a too-short piece the bolt handle will drop all the way, just "clunk". A too long piece requires some pressure to close the bolt. If you find one where the bolt almost but not quite drops to full close, that piece of brass is the size of your chamber. Base your measurements on that piece of brass.

There are lots of suggestions about how to set up the die. I don't need to get into that furball.

A comment about chamber prints, reamers, and headspace gauges and comparators. According to SAAMI, the headspace datum for a 308 win is 0.400 and the length is 1.634 minus .007. So the minimum chamber length at datum is 1.627. I have a Forster GO gauge marked 1.630 and Hornady comparator. I "compared" my headspace gauge. The comparator measurement I get is 1.626. Since the gauge is marked 1.630 and the comparator says 1.626, the comparator is about four thou short of the Forster length. I don't care that the comparator is different that the gauge. I use the comparator to measure a fired case and then measure that case after sizing. For that it works perfectly.

When sizing brass, I adjust my die (using shims) until I am getting minus two thou or 1.624. I get measurements between 1.6245 and 1.6235 using the Hornady comparator and a Mitutoyo digital gauge. When I get five in a row in the range, I size everything without further checking unless I feel something strange in the press stroke. I have found that annealed brass sizes much more consistently than unannealed brass. I use one of those frightening flame types - it works perfectly for me. I anneal the neck and the shoulder. If annealing didn't help, I would not do it.

In the past, I used the RCBS precision mic tools. They are very good but slower to use than the comparator.

EDIT: I checked my 308 Forster GO gauge with my RCBS precision mic. The RCBS gauge has a zero mark and 1 thou tick marks longer and shorter. The RCBS gauge says that my GO gauge is 2 thou shorter than zero. So either RCBS thinks that the headspace gauge is 2 thou shorter than the correct headspace or my Forster gauge is not 1.630 or the tools are measuring different places on the gauge.

 

[Marine52]

My Forster 308 Go & No Go set makes a tight chamber. New Lapua brass comes out of box at 1.608. My chamber fires to 1.611. So I size back to 1.608. Every factory 308 I’ve own fired to 1.620-21.

So I guess the benefit is my first and subsequent firings of the brass results in no appreciable change. I’m loading 1-2gr less of powder to get typical velocities.

The numbers you are giving are obviously from a comparator. Not true base-to-datum numbers. New Lapua 308 win cases are all within SAAMI cartridge spec which is 1.627” min base to shoulder datum.

 

[CK1.0]

Just set your die to bump the longest ones by 2 thou, done. (1.560"- 2 thou = 1.558")

After a few cycles/firings... check it again, and it'll probably still be fine, except maybe you'll notice that most of the cases now measure the same and are in the same neighborhood as the longer ones you've got now.

 

[davere]

It was said above inside a couple posts - but I'm reposting it for clarity so it's easier to find:

The comparator WILL NOT give you the "base to shoulder datum" number that you see on a reamer print or a cartridge spec diagram. It also will not give you a number that you can compare in an "apples to apples" fashion to another comparator - even one of the same brand, but definitely not between brands. What it WILL do reliably is give you a relative number you can use to compare between cases, gauges, etc, for shoulder bump and the like for things measured with your comparator.

A lot of good comments above around thoughts on why the variation, etc. I've seen the "new brass" variation bit myself, especially in cases where my new brass is a decent bit shorter than the chamber. In that case, I just pick the longest cases, and make sure those bump a couple thousandths, and then check them after the next firing.

If you have a full set of gauges, like nn8734 describes, you can determine relative chamber length (with your comparator), and determine what you need to bump to. If you had a GO gauge, you can kinda get close by progressively adding a "shim" to the base of the gauge until the bolt (without firing pin and ejector) won't just drop closed - typically, folks will use Scotch tape as the "shim". Measure each length, and bump to the last length that the bolt closes freely on - or thereabouts. It's not an absolute number, that way, but it gets you close enough. The whole idea is to bump the minimal amount that still reliably runs.

 

[CK1.0]

The comparator WILL NOT give you the "base to shoulder datum" number that you see on a reamer print or a cartridge spec diagram.

Explain this please..?

Because when I use a .375 bushing in my Hornady comparator with 6GT, and a .400 for 6CM, I see no reason why I shouldn't be measuring exactly what I think I'm measuring.

Here are the SAAMI drawings, notice the shoulder datums (.375 for 6GT, .400 for 6CM):

https://saami.org/wp-content/uploads/2022/01/Public-Introduction-6mm-GT-2022-01-28.pdf

https://saami.org/wp-content/uploads/2018/04/6mm-Creedmoor.pdf

 

[Max_The_Phoenix]

I had the hornady comparator set but today I remeasured the shoulder and cbto again with Short action custom set and wrote it in my reloading notebook. There is about .052 thou difference between the numbers I got with hornady but I don’t care since i am going to use the same comparators for next times and SAC has better build quality and the oring system is much easier to switch between heads and these are the numbers I can use as a reference.

 

[CK1.0]

The number really doesn't mean anything, it's just to generate a reference to use as a tool.

It doesn't matter what comparator one chooses to use.

But, if you're comparing against a spec, then yeah, you need to measure it as they measured it, thus you'd use the same datum (because that's what makes it a datum).

Some guys around here make water being wet seem hard to figure out.

 

[FLIGHT762]

Explain this please..?

Because when I use a .375 bushing in my Hornady comparator with 6GT, and a .400 for 6CM, I see no reason why I shouldn't be measuring exactly what I think I'm measuring.

Here are the SAAMI drawings, notice the shoulder datums (.375 for 6GT, .400 for 6CM):

https://saami.org/wp-content/uploads/2022/01/Public-Introduction-6mm-GT-2022-01-28.pdf

https://saami.org/wp-content/uploads/2018/04/6mm-Creedmoor.pdf

I'll explain it this way, I have two of the Hornady .400 inserts. One is very old, the other one was purchase a couple of years ago. I have a friend with a 1.630" GO gauge for 308 Win. and he let me borrow it. I measured the GO gauge with both of the .400 inserts.

The old insert measured 1.611" with the GO gauge. It's telling me that 1.611" equals 1.630 on the SAAMI GO gauge and it has a .019" chamfer on the edge of the insert. The newer insert measures 1.622" on the 1.630" GO gauge, indicating that .400 insert has a .008" chamfer on the edge of the insert.

Neither of the .400 inserts give me a measurement of 1.630". There's nothing wrong with either insert since they are a comparator. They both will give good, reliable measurements off of fired brass and can be used to set up F/L dies to bump case shoulders minimally.

Comparators don't give the same readings that you read off of a SAAMI case drawing. Don't expect them to.

 

[CK1.0]

I'll explain it this way, I have two of the Hornady .400 inserts. One is very old, the other one was purchase a couple of years ago. I have a friend with a 1.630" GO gauge for 308 Win. and he let me borrow it. I measured the GO gauge with both of the .400 inserts.

The old insert measured 1.611" with the GO gauge. It's telling me that 1.611" equals 1.630 on the SAAMI GO gauge and it has a .019" chamfer on the edge of the insert. The newer insert measures 1.622" on the 1.630" GO gauge, indicating that .400 insert has a .008" chamfer on the edge of the insert.

Neither of the .400 inserts give me a measurement of 1.630". There's nothing wrong with either insert since they are a comparator. They both will give good, reliable measurements off of fired brass and can be used to set up F/L dies to bump case shoulders minimally.

Comparators don't give the same readings that you read off of a SAAMI case drawing. Don't expect them to.

Ok cool, thanks. Fuck SAAMI and comparators!

 

[davere]

Explain this please..?

Because when I use a .375 bushing in my Hornady comparator with 6GT, and a .400 for 6CM, I see no reason why I shouldn't be measuring exactly what I think I'm measuring.

Here are the SAAMI drawings, notice the shoulder datums (.375 for 6GT, .400 for 6CM):

At one point, I had three different Hornady .400 comparators together in one spot. Using the same comparator body and calipers, and "zero"ing the calipers out (it was a dial, so basically, just noting what measurement each showed with the caliper totally closed, and then subtracting that number from each measurement), they differed by a couple thou when measuring the same case (I don't have the numbers saved - that was six years ago or so, now - I'm recalling that the spread was .003-.004?)

In theory, what you're saying should be right, but manufacturing tolerances get in the way. The one Hornady .400 comparator I still have on hand measures .399 ID. There's a radius on the corner, so at some point it's .400, but where is that relative to the bottom of the comparator (ie, "zero"). And, if the case is at all tilted, you get a different measurement with this style, too.

Other comparators (Sinclair, SAC, as examples) use shoulder angle to mitigate the "tilted case" problem - they are definitely *not* giving you anything like a measurement exactly at the datum point, but they tend to make it easier to get a repeatable measurement.

 

[ma smith]

I have found that annealed brass sizes much more consistently than unannealed brass.

Things that are not obvious to double check in your process: annealing state (level of work hardening) and the lubrication quantity.

Also there is measurement error inherent in the design of all calipers, hence they are only rated to ±.001.

 

[kthomas]

I had similar shoulder bump consistency issues, and it ended up being the Redding FL sizer I was using. Once I changed it out for a Whidden FL sizer, my sizing consistency issues went away. Every other part of my process stayed the same - how I lubed, how I worked the press, how I annealed, etc. What exactly was wrong with that Redding I don't know.

To achieve the most consistent results as possible, you need your process to be as consistently repeatable as process. Make sure you are doing things the same way each time. But sometimes our equipment can be the limiting factor, resulting in inconsistencies even when our process is as consistent as possible.

 

[DeathBeforeDismount]

I also trashed a Redding die and replaced it with a Wilson, which is heads and shoulders above every other $100 die. It solved my sizing issues as well. Have had bad luck with redding and just use Wilson and RCBS matchmasters (Cant beat $75 for a FL bushing set with micrometer sizer).

 

[Max_The_Phoenix]

Update:
Once fired Peterson brass:
Came out between 1.4845 to 1.486 which is about 0.0015 variance.
Measured using SAC headspace comparator.
Picked one of the cases with longest shoulder and Adjusted the die without bushing using wheeler method and bolt drops easy at 1.4845
Tighten the lock ring
Lubed all the brass on a tray using hornady one shot lube and sized all 45 cases using COAx single stage press
After resizing %85 of them came out at 1.483-14835 just a few at 1.4845

I think I should wait for second cycle of fire forming for more consistent shoulder bump after resizing, right?

 

[Max_The_Phoenix]

I went out yesterday with brass sized .0000-.005 from fired length. 600yds 308 20” 168 VLD. I wrote the numbers on the brass and mixed them in the mag. Had a 1/4 value variable wind 3-10mph 70F. (Beautiful range day)

I couldn’t leave the range with any difference in performance of note between the case sizes. Making matters worse I was shooting 243 brass in my 243AI with brass stretching all over hell and it was a laser beam. 12rnds under MOA. View attachment 8117947

Best thing of note was the ability to see the trace of all the rounds fired! I’ve never seen my own trace through the scope before. So it was a fucken riot and gave me a really good view of bullet flight.

My rifle is shooting 0.6 moa already with new brass but I have to resize the once fired brass to adequate number, looks like I still have brass spring back and all the cases are not formed the same amount and need to fire them again