Datums for Dummies

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mehavey said:
Okaaaayy.... You can close the bolt.

You haven't a clue as to how much excess space you now have.

.......... unless.... (drumroll please)

You know (a) the shoulder "datum" length at which the bolt juuuuust closes....
.and then (b) the shoulder length (pesky datum again) which the resized case now has.

That is all... ;)
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If you fire the case neck sizing until the bolt won't close on it and then set the die to where the bolt will close without rubbing the chamber, why do you need to know what the measurement is? You reach that point and even if you had excessive headspace, you have eliminated the problem! If I have excessive headspace in any rifle, I wouldn't know it. All my dies get set to FL size case's for one rifle chamber only! It is not necessary Knowing what that measurement is!
 
stagpanther said:
I'll bite--I bump shoulders back on cases all the time--what's false about that statement?:confused:
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I don't believe you can bump back a shoulder with out re-sizing the whole case the same amount. When the die push's on the shoulder at all, there has to be the whole case supported to keep the shoulder from buckling at the body joint some. What you actually do is FL the case just enough to move the shoulder far enough to let you again chamber the round. if you lock your die i at that point, you'll never have to neck size a case in that chamber again. It will always size that case in that die to what you have locked it into. You are FL sizing to the chamber in that individual rifle. I have 2 243's and bot are sized the way your saying. The case's from one set of die's will fit both chamber's. But the case's from the other dies fit only one chamber. Neither on has or had excessive head space I'm aware of and it one did, it would not matter at this point. Both set's of dies FL the case to fit the chamber of the rifle I dedicated them to.
 
Folks:
Many of the people in the machine and engineering trades are by necessity formally trained in the standards of Geometric Dimensioning and Tolerancing.

In USA,'The Book" is ANSI Y14.5
Its been several years,I'm a bit rusty but I was trained and certified.That was a requirement to be a machinist at a company that employed me.I understand there are ISO TC 10 and TC 213 that are used in Europe.
That does not make me so special. I would hope there are at least another million people in the USA who understand how to properly interpret an engineering drawing.

In terms of global manufacturing and trade,these are the "According to Hoyle" rules. When parts are contracted domestically or internationally, the drawing represents the terms of a contract.
Terms like "Datum" are clearly defined as they will be the terms that determine,in court if necessary,whether parts are good or not,whether suppliers get paid or not,and if a bad part made an aircraft fall from the sky.

It does not really matter what SAAMI,or Guffy,or Hornady,or Hatcher,or what I say a "Datum" is.

A "Datum" is what ANSI Y 14.5 says it is.

I suggest you look it up yourself. Then you know for sure my error or ego or agenda are not involved.

But for a real basic idea,a Datum is a theoretical line,point,plane,or even X,Y,Z co-ordinate system. You cannot hold it,touch it,make it,or buy a gunshow table of them.
You can disagree,you can make up anything you want,you can argue.

But a Datum is what ASME Y 14.5 says it is.

A drawing may designate the dimensions from a plane called Datum"A"

A calibrated granite surface plate may SIMULATE that theoretical plane,and we may set a part on that surface plate and inspect the part ,but the plate is not the datum. It represents the datum.

The circle that IS the SAAMI Datum to mearure headspace is SIMULATED by a headspace or bushing gauge. But those are not datums.



I'm not sure(Who can be sure what Mr Guffey is thinking) but I may have demystified Mr Guffey's riddle about how we do not move the case shoulder in the sizing die or in the rifle chamber.
Its a semantics argument.

In the sizing die set in the reloading press,with most presses,the die does not move. So,it does not set anything back.
The case shoulder comes against the shoulder in the die and stops. It does not move after that.
Perhaps that is the basis behind Mr Guffey's claim.
It may be argued that since the shellholder and ram continue to move,we are setting the case head forward,rather than the shoulder back.

OK.

If that s the point,(I don't know if it is) ,make the point and move on.
 
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For those who have posed variations on this reasonable response:
I've read through this thread a couple time's and hove absolutely no idea what this is about or how it would effect handloading. Your case either fit's the chamber properly or it doesn't. If it is to short you'll have a headspace problem if the case is resized to spec's and the chamber simply a bit to long. If the case is to long, the bolt won't close on the cartridge. If I have this measurement to the data line on the case fine, for what ever good it may be. But say I have it, how do you measure the chamber to find where it is in there without buying an extremely expensive tool of some kind to measure it.

It would seem to me that all I'm really interested in is hot the case fit's in the chamber and the datum line don't mean squat to me except for a discussion that seem's to be un-necessary for the average reloader. I don't care one bit about the datum line, I only case if my case fit's my chamber. So, where is this thread supposed to lead?
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Here is my attempt to give you an answer (since you asked)

Its a two part answer.

Part One) We all stand in a different pair of shoes. We have different experiences,and different pursuits . I have heard it said that reloading is slightly different than handloading. I don't want to take that to snobbery or elitism.
The guy with the Mallet and his Lee Classic reloader or the Lyman 310 tong tool is making ammunition that meets his needs.
He is happy. I have no will to rain on his parade. He might have no interest in any of this discussion because it has no application in his life.
That's fine. Lets leave him in peace.

And there are folks who only want to know "I put the key in the ignition,it goes. If not,I call AAA."

They aren't much interested in how "pinging" or detonation can cause a rod bearing shell to close in on the ends and scrape the oil off a journal.

But its not an offense that other folks discuss it.

Point: None of us will be at the top level of every discussion that comes around. I might not understand much about the Olympic sport of Curling.Thats OK. If you are into it,you might talk about it. I may not understand why its important. But,thats OK.

Please do not ask us to limit ourselves to discussions directly relate to your reloading needs. There is more.

Part two: (Of why we are discussing this)

A significant part of the discussions in reloading are around extending case life,head separations,stretch rings,setting dies,headspace,head clearance,bumping shouldes,etc.etc,etc.

Its like ringing the church bell. Soon we will be reading about "I buy gunshows of datums,I make datums,yadayada...and the water gets muddy,people get confused,etc. And no real useful information comes out. Just noise. If there is a point,it is not revealed in any useful way. Its just "I am the only reloader that...." The point is not to share or help,its to play an ego game.

The OP made an attempt to set things straight. I'm not sure it worked,but he tried.
 
What you actually do is FL the case just enough to move the shoulder far enough to let you
again chamber the round. if you lock your die i at that point, you'll never have to neck size a
case in that chamber again. It will always size that case in that die to what you have locked it into.
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No.

That setting will change with firings as the brass gets stiffer; And it will be different for different manufacturers.
If you don't know what the case is supposed to measure, you're flying by-guess and by golly blind each loading session.
Roll the dice.

Having been introduced to this fact on a hunting trip 25 years ago when the 243 began getting stiff to close, I learned fast.

But y'all do what you have to
 
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"Datum" is.

A "Datum" is what ANSI Y 14.5 says it is.
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Do not misunderstand, I am impressed with your ANSI Y 14.5, If I had a choice I would choose to be like me. reloaders claim the bolt will not close, I ask; "By how much?" You seem to be very desperate for attention, if you want attention and have all of that knowledge and experience of ANSI Y 14.5 why cant you use your skills to determine why the bolt will not close.

03 Experts claim Springfield never saw a 98 Mauser, I an not 03 expert, I have 5 of them, the first one I picked up I checked it out while someone was telling me how to check the head space/length of the chamber from the shoulder to the bolt face. I informed the smith I was interested in knowing the length of the chamber in thousandths; I was not interested in knowing if the bolt would close on a go-gage. He had no experience with ANSI Y 14.5. And then I informed him I could measure the length of the chamber 3 different ways without a head space gage. When the bolt closes the chamber gets dark inside for most smiths and reloaders, little things like the little light in the chamber going out does not lock me up.

And I am impressed with your granite stand, that makes me wonder where you were when L. Willis was selling his digital head space gage. I said his stand was a comparator, the case does not have head space and major manufacturers of gages and micrometers list the stand as a dial indicator holder. And then: There was his 3 point contact, that made reloaders giggly. He invented the three point contact and I wondered out loud; "was there a reloader that has ever milked a cow while setting on a 4 legged stool?"

Again: I have no ideal why reloaders feel threatened by the datum, you claim there is no use for them in reloading, I use a datum to verify a head space gage, there was a time I believed reloaders thought head space gages came from mars; me? I was convinced people made head space gages, I have three grinders that are used to make pilots, grind angles and grind to length, for those that can keep up the grinder is all the reloader needs in the way of tools to make head space gages. And the reloader should be able to verity the gage, I know of no other way except a datum based tool, if someone can make a head space gage they can make a datum.

I was checking Craig's List for tools being sold by owners and found 2 grinders, it is no surprise the grinders have been listed for 8 day.

I am a little distracted, my wife is OK but she totaled my P/U. As usual I did not receive what I thought I should, I purchased the P/U for the salvager price and decide to rebuild it. I was thinking it would take me 4 days after I got all of the parts rounded up. It is going to take 5, my traveling air compressor quit and my Milwaukee band saw failed me and my floor jack quit.

F. Guffey
 
I'll bite--I bump shoulders back on cases all the time--what's false about that statement?
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There are two members of this forum that have instructions for reloading presses, both have instructions for the A2 RCBS Press, the instructions identify the A2 as a cam over press, at the same time the instructions identify the A2 as a bump press. And then they claim the cam over press is a bump press. The instructions are different for the bump press/cam over press than for the non cam over press. the instructions for the non cam over press say the non cam over press is not a bump press. But the reloading forums are infatuated with bump, I have thought about referring to reloaders as being 'bumpers', it would not be nice because they have no clue as to what bump means.

All of my Herter presses are cam over presses, when I raise and lower the ram to the top the shell holder hits the bottom of the die twice, once on the way up and once again when the ram is lowered. There was a reason for the bump in the old days but since all reloaders have become experts the rational has escaped them.

And then there is the claim the reloader makes about moving the shoulder back. I claim I find it impossible to move the shoulder back, I have claimed my shoulders do not move and I have said it is impossible to move the shoulder back with a die that has full body support. I have made claims I have rendered cases scrap by moving the shoulder back. I have claimed I have turned cases into bellows and I have made cases look like accordions by moving the shoulder back.

We have a member that is an ANSI Y 14.5 expert, I believe there has to be a way to get him away from the key board to start sizing cease. I am convinced an ANSI Y 14.5 expert can figure out why it is impossible to move the shoulder back when sizing a case with a die that has full body support.

F. Guffey
 
1st:
DATUM is (by definition) "Reference point"
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And when you have a little experience and learn to use the datum you will discover 'all by your self' the datum is used to find that point.

F. Guffey
 
For all of that,Mr Guffey,
What did you say that helped someone understand something they were having trouble with?
What did you say that helped someone solve a problem?
What did you say that offers a new skill?

Picture a guy who shows up at a pot luck supper without bringing anything.
No big deal. Plenty to go around.
But when he goes around telling the folks who DID bring something "I'm the only one who knows how to make a coleslaw,mayo,and julienne Spam green jello mold,and you Swedes! You all think you know how to make meatballs!!
Let me tell you,I make Swedish meatballs,Greek meatballs,Italian meatballs,Scottish meatballs

No one but me knows how to make meatballs....etc.

But he brings NOTHING to the table.

Oh,and Steve:

I'll bet if he grinds his shell holder down he can bring yhat shoulder back.
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That might be a way I could gain some head clearance,But I believe I have a responsibility to chamber a rifle properly when I build it.
I use headspace gauges and its just not hard to cut a chamber to proper length.
I don't have ground down shellholders,or sizing dies.

Oh Mr Guffey:
As usual I did not receive what I thought I should, I purchased the P/U for the salvager price and decide to rebuild it. I was thinking it would take me 4 days after I got all of the parts rounded up. It is going to take 5, my traveling air compressor quit and my Milwaukee band saw failed me and my floor jack quit.
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I think I don't need to add much to that.
 
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That might be a way I could gain some head clearance,But I believe I have a responsibility to chamber a rifle properly when I build it.
I use headspace gauges and its just not hard to cut a chamber to proper length.
I don't have ground down shellholders,or sizing dies.
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I agree completely. When I was trying to go along with him wanting to leave me with a short chamber I did not want to buy the small based die and reduce the diameter of the case. The shell holder was cheaper to replace. Ultimately he tried to blame me for using a short shell holder and that it was MY alternative method that was to blame for what ended up being an issue of the lugs being set back during firing on top of the chamber being too short. I would like very much for him to try and sell his BS on this forum.

My review of his shop:https://www.google.com/search?clien...rd=0x535dcdecc337bf85:0xc7bf6df61ba8397b,1,,,
 
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I don't have ground down shell holders, or sizing dies.
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Good for you, I have said it is not necessary to grind the top of the shell holders down, I have said it is not necessary to grind the bottom of the die, I have said the Redding competition shell holders are not necessary.

I have said I have a 30/06 chamber that requires the die to be raised off of the shell holder .014" to obtain .02" clearance. Meaning? The chamber is .016" longer than a minimum length/full length sized case. Manufacturers do not make cases for reloaders that know what they are doing, To form/size cases for that chamber I use 280 Remington cases.

I could chamber 30/06 cases and pull the trigger.

F. Guffey
 
A "Datum" is what ANSI Y 14.5 says it is.
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I think I don't need to add much to that.
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You are the ANSI 14.5 expert. The first part I started looking for was the frame, There must be something different about my P/U, there is one available, it is stripped and over 1,000 miles away for $1,500 + shipping. So I crawled under my p/u with string and plump bobs and a gage I made that is 160"+ long, the frame is not bent. I am happy.

a gage I made that is 160"+ long
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I made a smaller one for measuring cases, can't talk about it because of snarky reloaders. The longest gage I have made was over 244" long.

F. Guffey
 
I made a smaller one for measuring cases, can't talk about it because of snarky reloaders.
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People are getting snarky towards you because you butt in to say how you are the only one... Instead why don't you explain how what you know would help whatever the thread is about. You come off like you think you are the master of the universe and nobody else can be as smart as you. Instead of proclaiming yourself as the only one who knows, why don't you explain how what you know can help whoever the OP is? You run people out of threads with your know it all comments that teach us little to nothing about how to solve the problems we are having. I appreciate that you obviously have some great experience and knowledge but it doesn't do me any good when I hear the canned answer from you which is, "I am the only reloader who measures from the head of the case to the shoulder in thousandths of an inch". Please say something helpful instead of gloating about being the only one who knows.

I am broke from learning a hard lesson with my gun or I would own the RCBS precision mic that is sitting on a shelf waiting for me. It does both of the things you tout. It measures chamber length and it measures case head to shoulder and it measures case head to ogive.

So.... Guffey, tell us how you make your"datums", how you use them and how it applies to the threads that you post in so that we might learn something useful besides the fact that you are the one who knows.
 
People are getting snarky towards you because you butt in to say how you are the only one... Instead why don't you explain how what you know would help whatever the thread is about. You come off like you think you are the master of the universe and nobody else can be as smart as you.
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https://www.theravive.com/therapedia/narcissistic-personality-disorder-dsm--5-301.81-(f60.81)

Symptoms of Narcissistic Personality Disorder

The definition of NPD states that it comprises of a persistent manner of grandiosity, a continuous desire for admiration, along with a lack of empathy. It starts by early adulthood and occurs in a range of situations, as signified by the existence of any 5 of the next 9 standards (American Psychiatric Association, 2013):

• A grandiose logic of self-importance
• A fixation with fantasies of infinite success, control, brilliance, beauty, or idyllic love
• A credence that he or she is extraordinary and exceptional and can only be understood by, or should connect with, other extraordinary or important people or institutions
• A desire for unwarranted admiration
• A sense of entitlement
• Interpersonally oppressive behavior
• No form of empathy
• Resentment of others or a conviction that others are resentful of him or her
• A display of egotistical and conceited behaviors or attitudes

Someone scores an eight out of nine in this thread!
 
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