February 11, 2018, 08:06 PM | #51 | |
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DATUM is (by definition) "Reference point" 2nd: It takes two points to establish your headspace dimension... be it Bolt face and/or case base as point #1 3rd: The DATUM -- for headspace purposes -- is usually the 2nd point: midway up/on the shoulder... be it chamber shoulder and/or case shoulder. The distance between those two points defines your Headspace Dimension. 4. WHY IT MATTERS: - If your case headspace dimension is longer than your chamber headspace dimension... you can't close the bolt. - If your case headspace dimension is much shorter than your chamber headspace dimension... you overstretch the case -- leading to early failure. |
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February 12, 2018, 10:06 AM | #52 | |
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And I suggest there has to be a lot of stuff going on the reloader does not understand. I have a M1917 with a chamber that is .011" longer than a minimum length/full length sized case. To save all the reloaders reading this I will save them time as in finding a pencil and paper. The chamber is .002" longer than a field reject head space gage. If what you claim about the long chamber the case would stretch .016" between the case head and case body. That is not what happens, if what you say is true the length of the neck would not change, if I fired a minimum length/full length sized cases in my long chambered M1917 the neck would get shorter meaning the firing pin did not drive the case forward; instead the case would get longer from the case head to the shoulder. The insults I get is the price I pay for disagreeing. If I did not have datums I could not verify a head space gage, I could not make a head space gage. When I started reloaders were using the Wilson Case gage as a drop in gage. The Wilson case gage is a datum based tool. The datum in the case gage has a radius, not a problem; Wilson understands datums, they start with the datum and then grind the case tool to length. Again, I have no ideal why reloaders are threaten by the datum. F. Guffey |
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February 14, 2018, 11:18 AM | #53 |
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Datum
noun, plural data [dey-tuh, dat-uh, dah-tuh] 1. a single piece of information, as a fact, statistic, or code; an item of data. http://www.dictionary.com/browse/datum I just ran across a whole herd of datums over at my bench when setting up for a load test using some new cases. I checked the Peterson cases for volume and found they average about 1.4 grains of water less than the volume of the Lapuas. A couple of datums right off the bat. This datum told me not to expect the same velocities and SD's using the same powder load, primer, and seating depth in the Petersons that I used in the test last week using the Lapua cases when setting up the sizing die I used my Hornady headspace comparator with to find a datum using a case that had been fired in that rifle but not sized. I took into account the brass springback but since that is minimal it really does not make enough differance to sweat. I could have also used my PTG Go gage to get that datum had I wanted to be super precise. Then I used the datum to set my sizing die to give a .003 shoulder bump when resizing the cases. Oops that .003 would be a datum also. When I calibrated and zeroed the chargemaster and my beam scale. 2 happy little datums scurried off to the land of data When I decided to start my load test, I used the datum of 38.2 grains of Varget for a a starting weight. Once I finished loading powder into the cases I needed to set my seating die so out came the rifle and my trusty Hornady OAL gage and the bullet comparator along with a .264 datum insert. I used 5 bullets to get an average of distance to the lands and then I had the datum needed datum to determine where I needed to set my die to get distance of .25 from the ogive to the lands. I adjusted my seating die to just barely get the bullet into the neck and measured it with the Hornady gage and there was another datum. This datum was used to determine how much I needed to adjust the die down to get a .025 distance from the ogive to the lands. Datums are everywhere in reloading and in everyday life as well
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February 14, 2018, 11:53 AM | #54 |
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Datums? Rumor control has it they taste like chicken. There are many ways to prepare them with deep fried with a light flour and beer batter being the most popular. Many forums invite members to share their recopies for datums.
Ron |
February 14, 2018, 12:01 PM | #55 | |
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Back to determine bolt closing: All I am looking for is the "BY HOW MUCH". A reloader, a smith does not need a head space gage, they do not need a datum, I believe they get lost when they start talking it to death. In the old days it would not have taken 20 seconds out of a soldiers life to measure the length of the chamber from the shoulder to the bolt face (in thousandths) ever day. And then there was Hatcher, same thing. F. Guffey |
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February 14, 2018, 12:13 PM | #56 | |
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February 14, 2018, 06:19 PM | #57 | |
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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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February 14, 2018, 07:49 PM | #58 |
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Hatcher's Notebook beginning on page 232 for the linked version has some interesting reading and reference material for the shooters, gunsmiths, ballisticians, hunters and collectors. Julian S. Hatcher shares his views and experimentation results on the subject of headspace. Some of the experiment results are interesting material, especially those involving excessive headspace intentionally created.
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February 15, 2018, 09:23 AM | #59 | |
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Reloaders assume they can move the shoulder back when sizing the case, I say it is impossible to move the shoulder back when sizing a case with a die that has case body support; and the very next day after saying it is impossible to move the shoulder back with a die with case body support all the reloaders on all reloading forums claim they bump the shoulder back and I ask, "How do you do that?". And then they claim they move the shoulder forward when they fire the round; I say the shoulder does not move forward when sized and the shoulder does not move forward when fired, I claim my shoulders do not move. And then there is the claim the case, powder and bullet takes off for the front of the chamber when the primer is hit with the firing pin; and I ask how would a reloader determine if there was any truth in that story. Hatcher did not get the results he anticipated, I chambered an 8mm57 round in an 8mm/06 chamber, I pulled the trigger, I ejected an 8mm06 with a very short neck. F. Guffey |
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February 15, 2018, 11:38 AM | #60 | ||||
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You seem to like going off about the term bumping or moving the shoulder back but never once explained your thoughts on the subject. Quote:
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Ron |
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February 15, 2018, 12:44 PM | #61 | |
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February 15, 2018, 12:48 PM | #62 |
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I'll bite--I bump shoulders back on cases all the time--what's false about that statement?
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February 15, 2018, 01:25 PM | #63 |
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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.
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February 15, 2018, 01:59 PM | #64 |
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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. Last edited by HiBC; February 15, 2018 at 08:50 PM. |
February 15, 2018, 03:42 PM | #65 | |
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For those who have posed variations on this reasonable response:
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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. |
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February 15, 2018, 06:22 PM | #66 | |
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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 Last edited by mehavey; February 15, 2018 at 06:31 PM. |
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February 15, 2018, 06:23 PM | #67 |
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Thank you, HiBC.
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February 16, 2018, 11:35 AM | #68 | |
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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 |
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February 16, 2018, 12:09 PM | #69 | |
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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 |
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February 16, 2018, 03:47 PM | #70 |
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I'll bet if he grinds his shell holder down he can bring yhat shoulder back.
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February 16, 2018, 04:26 PM | #71 | |
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1st:
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F. Guffey |
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February 16, 2018, 05:53 PM | #72 |
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The datum is a reference point.
It is not some kind of tool in search of it. |
February 16, 2018, 09:44 PM | #73 | ||
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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: Quote:
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: Quote:
Last edited by HiBC; February 16, 2018 at 10:12 PM. |
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February 16, 2018, 09:53 PM | #74 |
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Touche!
Last edited by Yosemite Steve; February 17, 2018 at 10:16 AM. |
February 16, 2018, 10:13 PM | #75 | |
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My review of his shop:https://www.google.com/search?client...61ba8397b,1,,, Last edited by Yosemite Steve; February 17, 2018 at 10:17 AM. |
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