Hornady Headspace Comparator, questions

[Shadow9mm]

So I just got my Hornady Headspace Comparator tool in. Having some issues with 6mm arc and a possible oversized chamber. In any case I took my first set of measurements today. and had some questions. Mainly what is the acceptable variance in these measurements? Given good bullets, when using my bullet comparator, I generally get one number, say 1.156. and out of say 20 measured I might have 1 at 1.155 and one at 1.156, but the vast majority are all at 1.156. basically a small sampling at +/- 0.001.

Brass is Hornady and was factory loaded new and has just been resized for the first time. I was fortunate to have 10 unfired factory rounds left which I measured for comparison

Factory new ammunition
7 at 1.184
3 at 1.183

Once fired first resize
5 at 1.182
4 at 1.183
1 at 1.184

Out of curiosity I also measured my go/no-go gauges.

Go 1.184
No-go 1.190

Unfortunately I don't have any fireformed brass to measure, but I am hoping to next week.

But back to the main question. How much variance is normal and or acceptable when measuring sized brass from cartridge base to a point on the shoulder (headspace).

 

[scatterbrain]

Shadow, .001 isn't bad, unless you are trying for 0 SD, or .01 group size. The first thing I learned about measuring every case is that every case has to be prepared the same, including lube. I do the very best I can and except .0005 in length. If more, I lube again and retry. The same for run out, if more that .0005 I resize and try again. All my brass is pen cleaned, annealed and sorted by 1 grain increments, I do try for 0 SD and .001 group size, I am never going to achieve that, but it's been a learning experience trying to do so. My hunting rifles will give me .25" groups, sometimes.

 

[HiBC]

If I want to machine a part to .001 or .002 tolerance, I don't measure with calipers.
However,generally the number I would get using the Hornady type measurement is not a dimension on a print. It does not "qualify" your part good or bad. Its a semi-meaningless reference number. A starting place for a comparative measurement. What you need to know is how much the brass changes when you size it.
You will get some variation ,probably, if you measure the same case 5 times. Especially if you close your eyes, feel "Thats it" then open your eyes.

Don't drive yourself crazy with it. Its a tool that will help you set your dies so
A) You will be able to close the bolt and B) Head clearance will be controlled for case life.
Thats a good tool to have.

A tool that is a more costly way to go and slower to use is the RCBS Precision Mic. Its a micrometer head sort of gizmo you take apart,load your case in,then you are measuring with the micrometer head.

I may have bought one once, Its not the system I use. But it will give you nice numbers. You'll feel Precision!

 

[tangolima]

With calipers, even in trained hands, tolerance of +/-0.001" is expected. More if untrained.

You need to have some before sizing brass to measure. Looks like your sized brass is one the short side.

I don't have any fancy gauges. I take a fired brass. Remove the expander from the sizing die. Raise the die higher. Size and try chambering it in rifle. Lower the die by 0.002" and repeat, till it chambers without felt resistance. Then I lower the die further 0.002" for bolt gun and 0.004" for semi auto or lever action.

-TL

Sent from my SM-N960U using Tapatalk

 

[stagpanther]

You're firing a stepchild of the grendel, so as long as you're set-up conforms with the go/no-go guages then there is likely no headspace problem, what you want to aim for is minimize working of the brass between resizings--so you want to get a good idea of how much expansion there is in the brass--allow enough to work safely and reliably but not so much the brass is over-worked after resizing. Grendel brass is a bit prone to flow/growth in my experience. This means that simply dialing down the die to touch the shell holder may not be enough (never is for me with grendel brass fired several times). ARC brass in my experience behaves the same way. Grendel-based cartridges also "tempt" hot loads for max velocities, so that too is going to stress the brass, maybe even before you see any primer pressure signs. My primer pockets usually go first before anything else fails with a grendel based case.

 

[Shadow9mm]

You're firing a stepchild of the grendel, so as long as you're set-up conforms with the go/no-go guages then there is likely no headspace problem, what you want to aim for is minimize working of the brass between resizings--so you want to get a good idea of how much expansion there is in the brass--allow enough to work safely and reliably but not so much the brass is over-worked after resizing. Grendel brass is a bit prone to flow/growth in my experience. This means that simply dialing down the die to touch the shell holder may not be enough (never is for me with grendel brass fired several times). ARC brass in my experience behaves the same way. Grendel-based cartridges also "tempt" hot loads for max velocities, so that too is going to stress the brass, maybe even before you see any primer pressure signs. My primer pockets usually go first before anything else fails with a grendel based case.

I did buy and check the gun with headspace gauges, go went, no-go did not. That is one thing I ALWAYS check when putting a rifle together. I have yet to have a rifle fail gauges, but it gives me peace of mind.

Minimizing sizing and extending brass life is the goal. Getting brass has been difficult so far, as I am not ready to jump into forming my own just yet. I am working with 100pcs from factory ammo and have some starline on backorder, so i HAVE to take care of what I have.

My concern is that my chamber may be overly roomy. Seems that the brass grew a lot, and widened out in the body/shoulder a fair bit as near as I can tell. seeing as my other gauge would not work due to these issues I bought the Hornady Comparator kit so I can measure a find out a bit more.

On a side note L.E. Wilson got back to to me about their gauge and told me I could send in a few fire-formed pieces and they would give me a better idea of what is going on. I will be doing that once I can get to the range have some. But like you said this cartridge may just be prone to growth. a unforseen CON to the cartridge.

I will be curious to see how the primer pockets hold up. Especially between the Hornady brass and the Starline, once I get it. If anything I expected them to hold up better than 223 since they use small rifle primers and have a larger case head.

I do plan to test up to max, or as far as I get. I just want to know where the limit is and that I am safely below it. I am using Hornady's gas gun data as it is an AR, so hopefully I should not be overly stressful on the brass. I expect the bolt gun data would ruin brass fairly quickly.

 

[stagpanther]

At first I thought you were referring to growth in the shoulder datum as measured in a comparator, but it seems you are saying that the diameter of the chamber is too large (?). I guess I should clarify by what I meant about "prone to growth"--it's not a defect in the brass itself--just that it readily is going to flow if you have a pretty big size difference between the chamber's shoulder datum and that of your sized case.

All my ARC brass is made from grendel cases--it's very easy and straightforward with no need for extra turning in my experience; all the ARC brass is is grendel with the shoulder set slightly back and the neck sized down (possibly a slight angle in the shoulder change, not sure about that, but that will form upon firing) , but a bit of that brass from the shoulder will end up in needing the case length needing to be trimmed a bit--just a few turns on a trimmer; not a massive pile of shavings trim job. The only real downside is if you have grendel chambered rifles and then sorting brass can be a bit of a pain if you fire them around the same time.

 

[Nathan]

First, there is a cbtd drawing dimension on the SAMMI print, but these gages don’t really measure that for some reason. It has to do with the gage design.

If does give you a number to compare to…..so, you should be comparing fired in your rifle dimension to sized in your die dimension.

That difference is typically 0.001”-0.006”. In a bolt action rifle, 0.002-0.003” is a nice place to be generally. You are generally trying to size to the point where the action closes easily on each case. With just the bolt body, you can feel the point where the case is sized enough for the handle to just drop. That is about perfect.

Then you will want to measure cases you size and look at your variation. This is where you will go nuts with better dies, stiffer press, annealing, Lapua brass, etc chasing zero variation in cbtd and neck runout!

Welcome to the Hotel California!

 

[ocharry]

shadow...just curious here about your resizing

are you using a bushing die to set the shoulder back and then using a mandrel for neck tension....or... are you using a standard die with the expander ball???

if you are using the expander ball type and the inside of the neck is not lubed well enough you could be pulling the neck up...making it longer so you could be making the different size when you are sizing...just a thought

you know i get that you want to make this thing shoot as good as you can but i think if i was going to try and make a 1 holer i would not have picked a gas gun to do it with...bolt is where i would have went

not saying you cant get a gas gun to shoot well and some do really well

not trying to be a dick here but i think you are chasing a ghost....measure a fired case push the shoulder back .004-.005 and load them for groups

i bet when you start measuring the fired cases out of your gun you will have more of a spread of .001

in a perfect world i agree you should be able to put a brass in the press and into the die and every single one of them would measure the same....BUT in reality that just may be something that dont happen...the brass may not be the same, sprng back could be different from piece to piece....pressure on the ram could be different...lube inside the die could be different or on the case....lots of different things could be causing the .001 you are seeing

i hope i havent offened you or anyone else here...but i think you are chasing a rabbit down the proverbial hole ...maybe not...some people just like the chase...my boy is like that...lol...yep i have asked him many times is he had the rope tied off good and good knots

good luck on you quest...but i would set them cases back and start loading and shooting and not sweet the small stuff....well unless you are going to a match with eric and the boys...then you need you AAA+++ game...lol

good luck

ocharry

 

[Shadow9mm]

Ocharry

Using a standard sizing die. The ball could be a contributing factor, good though. After my next session when i can get some more measurements i will know more.

I find that much can be learned going down rabbit holes. In this case i am trying to determine if there is an issue with my chsmber. And with the new gauges stumbled upon other questions. How much variance is normal. Is it an issue.if it is an issue hiw much difference does it really make. The last step, if it is an issue, and makes enough difference to look for a fix, how to go about it. And possibly other questions i have not even come across yet.

 

[stagpanther]

I have occasionally seen excessive pressure on the case when seating or roll crimping with a seating die is enough to press down on the shoulder causing an "outside donut" on the shoulder/case body junction.

 

[Shadow9mm]

I have occasionally seen excessive pressure on the case when seating or roll crimping with a seating die is enough to press down on the shoulder causing an "outside donut" on the shoulder/case body junction.

Interesting. Perhaps they made the case walls too thin to increase case capacity to gain performance?

 

[stagpanther]

Interesting. Perhaps they made the case walls too thin to increase case capacity to gain performance?

Not likely--when done right they should last a long time through many repeated firings. I tend to find hornady brass is a bit more "elastic" than others (not to sound like I'm picking on them, just my experience).

 

[tangolima]

OP. You worry about the chamber size. A chamber cast is the base way.

If the chamber is indeed cut over sized, replacing it is of course the best option. If not, it is still not too bad. The sizing die will squeeze the fired brass back in. It certainly will over work the brass body. The solution is then in the sizing die. Some brands are roomier than the other. Some manufacturers even take custom orders to hone their sizing die bigger. It is ok if you load for this particular rifle.

You may not want to hear that after spending money on gauges of different sorts. You load for your rifle, not to sell your ammo to your customers. Meeting saami specs is not necessary.

-TL

Sent from my SM-N960U using Tapatalk

 

[Shadow9mm]

OP. You worry about the chamber size. A chamber cast is the base way.

If the chamber is indeed cut over sized, replacing it is of course the best option. If not, it is still not too bad. The sizing die will squeeze the fired brass back in. It certainly will over work the brass body. The solution is then in the sizing die. Some brands are roomier than the other. Some manufacturers even take custom orders to hone their sizing die bigger. It is ok if you load for this particular rifle.

You may not want to hear that after spending money on gauges of different sorts. You load for your rifle, not to sell your ammo to your customers. Meeting saami specs is not necessary.

-TL

Sent from my SM-N960U using Tapatalk

I agree, a chamber cast is the best way to get my chambers dimensions. However its a step and process i dont feel i need to take as of yet. I will measure, and send some brass off to wilson, and see what they say since they offered. If those results look excessive i will contact ballistic advantage and see what they reccomended.

With any luck the chamber will just be a bit roomy and i will be able to adjust my dies according and keep on shooting. But i need to measure and check for now.

 

[Shadow9mm]

So, just measured the brass i fired. Got a growth of 0.008 compared to factory loaded ammo and 0.009 compared to my currently resized brass.

Gonna adjust for a 0.003-0.004 bump.

 

[Unclenick]

That's reasonable. The SAAMI minimum chamber spec is 0.0071" bigger than the minimum cartridge. The SAAMI maximum chamber is 0.010" bigger. Most ammo makers are within 0.001" of the minimum or close to it, and most new chambers are 0.002-.004" above the minimum, especially in a self-loader's chamber. So, you're falling right in there somewhere.

 

[Shadow9mm]

That's reasonable. The SAAMI minimum chamber spec is 0.0071" bigger than the minimum cartridge. The SAAMI maximum chamber is 0.010" bigger. Most ammo makers are within 0.001" of the minimum or close to it, and most new chambers are 0.002-.004" above the minimum, especially in a self-loader's chamber. So, you're falling right in there somewhere.

That makes me feel much better, thank you unclenick! I will just adjust my dies for a bump to save some case life. Should give me a nice safety margin in presssure as well.

 

[HiBC]

I suggest you make a paper clip probe and monitor stretch ring.

 

[ocharry]

hey shadow...dont know if you are interested or not or you dont want anymore but

sixfiveoutfitters has starline 6arc brass right now for $68

saw that and thought of you...if its really hard to find things i like to get extra when i can

just thought i would pass it along

ocharry