300 win mag headspacing

Today, 06:34 AM #20
HiBC
Senior Member


Join Date: November 13, 2006
Posts: 2,942 Datums

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From ASME Y14.5 2009: "Geometric Dimensioning and Tolerancing"

Datum — A theoretically exact point, axis, or plane derived by contact a datum feature; it then becomes the origin from which geometric characteristics are measured.

You cannot buy a datum.Datums are theoretical geometric features,such as planes ,axis,etc..




I make datums, I purchase datums, I collect datums, I thought the reloading forums had moved beyond believing the datum is beyond their ability to understand and or comprehend. When I first started the holy grail was a drawing with an arrow pointing to a line labeled datum line, the total amount of information understood from the drawing? “It is measured from this line and that is how it is done”, no one understood the concept.

If someone choses to use a set-up table I will help them, and, at the same time discourage them for doing such a dumb think. I have a steel set-up/layout table, drilling through the table would be mindless, something like grinding the bottom of a die and or top of the shell holder, it is just not necessary.

The datum is a round hole/circle, anyone with a drill index set of drills and a means of drilling a straight hole is very capable of making datums, I am convinced they (reloaders/smiths) can do it, problem? It seems they are afraid if they take the time to understand the concept they will be required to ‘do it’.

Anyone that can not drill a 3/8” hole is very short on shop skills, the 3/8” hole is the .375” datum for the 30/06, 270 Winchester, 280 Remington, 25/06, 7.7 Japanese on and on etc..

“Datum — A theoretically exact point, axis, or plane derived by contact a datum feature; it then becomes the origin from which geometric characteristics are measured”

Measured from, measured from the datum, the length of the case is measured from the datum/shoulder to the head of the case. The case sets on the top of the hope, the hole for the 30/06 is .375” in diameter, when measuring from the surface the hole is drilled through the reloader is measuring from the datum, measuring the length of the case from the head of the case down to the surface of the plate the hole is drilled through will indicate the length of the case ‘from the datum to the head of the case’.

A plane!, a plane! The plane is the surface the hole is drilled through, the point measured from is located at the .375 intersection on the shoulder, again, the shoulder is tapered, the shoulder is round, the round tapered shoulder forms a cone, a cone has varying diameters, and that is what locks everyone up, the diameter ‘WE’ are looking for on the shoulder with varying diameter shoulder is .375. the only way to find the .375” diameter location on the shoulder is with a straight 3/8” hole drilled through a flat surface called a plane.

The 308 Winchester 243 Winchester etc., datum is .400”, for most that get driven to the curb that is it, not me, because of the tapered shoulder that forms a cone, I can use .375”, .340'” etc..My chamber, my dies, my cases,
my reamers and my gages. It has taken years to get reloaders pass the arrow pointing to a line labeled datum line,

The L. E. Wilson case gage has been around since the 50s. The shoulder of the case when placed in the gage is supported by’ THE DATUM’, the datum at the bottom of the L E. Wilson case gage for the 30/06 is .375”.

Back to HIBC
“
Datum — A theoretically exact point, axis, or plane derived by contact a datum feature; it then becomes the origin from which geometric characteristics are measured”

My opinion, HIBC you would not recognize a datumn if you were looking at one, again, again, the Wilson case gage has a datum.

If ‘you’ in your post was not referring to me, forgive.

F. Guffey
 
“Measured from, measured from the datum, the length of the case is measured from the datum/shoulder to the head of the case”

Not complicated, head space is measured from the datum to the bolt face, I know, I said length of the case, then there is SAAMI, SAAMI says etc.. SAMMI does not list head space for the case, SAAMI list head space for the chamber from the datum to the bolt face. Back to not complicated, I off set the length of the chamber from the shoulder/datum to the bolt face with the length of the case from the shoulder/datum to the head of the case.

F. Guffey
 
Guffey, SAMMI does list head space for the .300 Win Mag case. They do for all rifle cases. Check the following SAAMI info noting the red-circled dimensions for what's commonly called "case headspace." Note the .300's got two of them; one for the case belt headspace and one for the case shoulder headspace. Case shoulder headspace is the one most often meant by the term.

8527082011_e879e17a5d_z.jpg


8527062675_9bfcb42ded_z.jpg


There are gauges made to measure case headspace by Hornady and RCBS.
 
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Bart B.

http://www.saami.org/PubResources/CC_Drawings/Rifle/30-06 Springfield.pdf


B=BASIC
Below the bottom line SAAMI has added notes referred to as ‘NOTE’, something like, Readers note we have measurements in thousandths of an inch and metric measurements.
Then there is HEADSPACE DIMENSIONS, as in: Readers we use the circle with an x in the center to bring your attention to ‘headspace’.

Omitted from your post of ‘Cartridge and Chamber’ is the chamber drawing, omitted from your cartridge drawing is a mention of headspace, and, NOTE they as in SAAMI made no reference to head space as in referring to a circle around an x referring to head space and the cartridge.

Can not be an a mistake, they were consistent, I do not assume ‘it’ is there. Again, it can not be that complicated, I want to know the length of the chamber from the shoulder/datum to the face of the bolt and I want to know the length of the case from the shoulder/datum of the case to the case head, A – B = C when C represents the difference in length between the chamber from the usual places and the length of the case from the usual places.

2.048” Minimum 2.058 Maximum as in note, we did not have enough room to etc.,etc., so we used a symbol to note head space, again, absent in cartridge drawings.

I want to know the length of the chamber from the shoulder/datum to the face of the bolt in thousandths, everything after that is about transfers, standards and verifying, the humble feeler gage can be used to transfer, it can be used as a standard and it can be used to verify.

F. Guffey
 
Guffey, your comments are exactly what I thought they would be.

All I was doing was referring to the case dimensions measured by gauges made to do so so one could compare the fired case dimension to a full length sized one. Since such case headspace gauges have been available for decades and the term's been used just as long or longer, I thought I would mention it. Your rhetoric doesn't change those facts. Most folks very well understand what I'm referring to and have no problem with it whatsoever.
 
40 years ago,as part of going to the trouble of smoking my case shoulders to see when the made contact in the sizer die,I used feeler gages,and included one in my die box,matched to that die and shell holder.

And,I understand how one can custom taylor ammunition to compensate for a worn gun with excessive headspace,or even one that a poor gunsmith made with excessive headspace .

Its OK if I prefer to use a Wilson case gage with a little granite comparator stand and indicator to do it my way.It works just fine.

I like to use my Starret multi-anvil mic ,with the anvil and clamp removed,to mic the protrusion of the headspace gage.No,I do not shoot headspace gages,but I use them.I strive for just feeling,but not crushing,the "Go" gage.

I have never had a chamber accept a "no go" that I chambered.If I did,I'd set the barrel back and start over.

I am quite sure I can read the drawing,and I am quite sure I understand headspace.

I am sure Mr Bart B,Clark,and AR-15 Barrels do ,too

Mr Guffey,I'm sure you have a great deal of experience,knowledge,and a lot to share.Thank you.

There is a bit of a style issue.It is unnecessary to set on the stool and lecture us about what we don't know.The fact is,you have no way of knowing what we know,therefore,when you talk about what we do not know,you do not know what you are talking about.

Some might find it useful if you would say:

"In my experience,you can use a feeler gage to....."

That would be sharing the gold.

The rant about how dumb everyone is,could be left out.

If I were to make a datum reference bushing to rest on a cartridge case shoulder,I might use a drill to rough the hole,but then I would bore the hole and use gage pins to measure it.

I suppose I could make up a set with tangs on them to mount on my Sylvac height gage,but,I probably wont.It would work good,though.



I do it a little different,but thats OK.
 
“If I were to make a datum reference bushing to rest on a cartridge case shoulder,I might use a drill to rough the hole,but then I would bore the hole and use gage pins to measure it”

March 3, 2013, 06:34 AM #20
HiBC
Senior Member


Join Date: November 13, 2006
Posts: 2,945 Datums

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From ASME Y14.5 2009: "Geometric Dimensioning and Tolerancing"

Datum — A theoretically exact point, axis, or plane derived by contact a datum feature; it then becomes the origin from which geometric characteristics are measured.

You cannot buy a datum.Datums are theoretical geometric features,such as planes ,axis,etc.

We can use tools to represent datums ,for example,a granite surface plate may be used to represent a datum plane.Or,as in the Hornady case length caliper gage,the ring privided will rest on the case shoulder to give a useful approximation of the datum .

ASME Y14.5 is THE standard for what terms and definitions apply to engineering drawings.

I am quite comfortable working with it.

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Last edited by HiBC; March 3, 2013 at 06:44 AM.



“You cannot buy a datum.Datums are theoretical geometric features,such as planes ,axis,etc..

Progress? You start with “YOU ( I ) can not buy a datum”: A round hole used to locate a diameter on a tapered cone. Now you are using a pin gage to measure the diameter of the hole through a plate that uses the surface as a plane. “You can not buy a datum” again, there is a datum in the bottom of the L. E. Wilson case gage.

I said I make datums, I collect datums, ‘collecting’ If I am unable to buy them ‘datums’ how can I collect them? Hole gages, wire gages, bolt gages, that would be plates with lots of holes, a datum is “measured from” the plate surface would become ‘THE PLANE’, just a reminder, the holes will have a radius, the radius will lower the plane below the surface.

HIBC,

“The rant about how dumb everyone is,could be left out.

If I were to make a datum reference bushing to rest on a cartridge case shoulder,I might use a drill to rough the hole,but then I would bore the hole and use gage pins to measure it.

I suppose I could make up a set with tangs on them to mount on my Sylvac height gage,but,I probably wont.It would work good,though”

It would be dumb to drill a hole through a set-up table. I did not ask you how you would do it, most owners/users of pin gages also have a pile of reamers as in +.001” or –.001”.

If you thought the bolt nose was hitting the barrel you should have explained to the proud owner of all those parts how to determine if the bolt face was hitting the barrel, I did, I suggested removing the bolt, then screw the three parts together ( receiver, lug and barrel) first then install the bolt, I went on to suggest backing the barrel out until the bolt closed. After the bolt closed when the barrel was baked out the distance the barrel was backed out could be measured with a feeler gage when measuring the gap between the receiver and recoil lug. You choose to insist I agree with you. I was addressing the OP’s problem, I was not addressing.

AR15Barrels insist I open the link he provided, “That works great IF you know where your boltface datum is and you have a way to take accurate measurements on the barrel” Over and over, the ‘measure from’ is the datum, the datum is on the shoulder of the chamber. The datum/round hole for the 300 Win Mag is .420”, again the bolt face is the measured to from the measure from (datum) .


“Mr Guffey,a problem with using cartridge cases for gages is the cartridge cases vary,and the cartridge case makes a poor gage” “The rant about how dumb everyone is,could be left out” :rolleyes:

“using a cartridge” “the cartridge cases vary” Back to standards, transfers and verifying. Depends on who is measuring, practice, practice, practice. When screwing two pieces together felt resistance is critical, I have no problem verifying the length of a case from the head of the case to its shoulder, because I can, and I still have the instructions from the barrel manufacturer with Plan A and Plan B. Again, I did not ask you what you thought of using a case. I did consider that I are surrounded with with equipment and tools, I did consider the OP and his tool situation. He did say he was doing his first belted magnum.

F. Guffey
 
Yesterday, 08:45 AM #24
Bart B.
Senior Member


Join Date: February 15, 2009
Posts: 1,752 Guffey, SAMMI does list head space for the .300 Win Mag case. They do for all rifle cases. Check the following SAAMI info noting the red-circled dimensions for what's commonly called "case headspace." Note the .300's got two of them; one for the case belt headspace and one for the case shoulder headspace. Case shoulder headspace is the one most often meant by the term.




#26
Bart B.
Senior Member


Join Date: February 15, 2009
Posts: 1,752 Guffey, your comments are exactly what I thought they would be.

All I was doing was referring to the case dimensions measured by gauges made to do so so one could compare the fired case dimension to a full length sized one. Since such case headspace gauges have been available for decades and the term's been used just as long or longer, I thought I would mention it. Your rhetoric doesn't change those facts. Most folks very well understand what I'm referring to and have no problem with it whatsoever.
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“All I was doing was referring to the case dimensions measured by gauges made to do so so one could compare the fired case dimension to a full length sized one....”

If that is all your were doing the second post would not have been necessary, Sinclair/Hornady and L, Willis took took liberties when they labeled comparators as head space gages, again, L E. Wilson calls their case gage a case gage.

“Exactly what you thought” You remembered, this is not the first time you have referred to the case as having head space, my cases have a length that is most useful, the length from the shoulder/datum to the head of the case. My chambers have a measurement called head space, SAAMI makes reference to head space in their chamber drawings, they do not use the reference (note) “head space’ in the case drawings. There are chamber gages and there are case gages.

A side note: A manufacturer of reloading tools ask me to agree with him, his rational? He believed the reloading industry would be better off if I agreed with him. I have the luxury of disagreeing, if I am not given the luxury, I take it.

F. Guffey
 
F. Guffey said:
AR15Barrels insist I open the link he provided, “That works great IF you know where your boltface datum is and you have a way to take accurate measurements on the barrel”
Click to expand...

A machinist (gunsmith) is only as good as his tools.
If you don't have a depth gauge, you probably should not be chambering barrels.
 
Today, 02:27 AM #30
AR15barrels
Member


Join Date: August 23, 2006
Location: Los Angeles, CA
Posts: 48 300 win mag headspacing

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Quote:
Originally Posted by F. Guffey
AR15Barrels insist I open the link he provided, “That works great IF you know where your boltface datum is and you have a way to take accurate measurements on the barrel”

A machinist (gunsmith) is only as good as his tools.
If you don't have a depth gauge, you probably should not be chambering barrels.



AR15BARRELS. I honestly believe you can do better than that, I know a few proud owners of some very fine tools that have absolutely no ideal how they are used. I get the most out of the least amount of tools. I am the one that can check the length of the chamber from the bolt face to the shoulder/datum with the bolt closed. Again, the bolt face is not a datum, it is a plane without the datum, the datum is used to find a location/diameter on the shoulder of the case, shoulder of the go, no and beyond-gage and chamber. The datum is the ‘measured from’ the bolt face is the ‘measured to’.

Height gage, depth gage, then there are those old transfer calipers, and the dial caliper, it is inside, outside and a depth micrometer. I have no infatuation with head space gages, there are only three between .000 and .016”+, there are no chamber length gages on the .000-(negitive) side. I make chamber length gages from .012 shorter than minimum length/full length to .016+, that is 28 different length. Tools? I also have an in-line, angle and butt grinder. I am not the one that thinks head space gages come from mars, people make gages, I am a people.

“A machinist (gunsmith) is only as good as his tools.

If you don't have a depth gauge, you probably should not be chambering barrels”

AR15BARRELS, my opinion, you should make an attempt to work with the OP, do the best you can do to serve him, that is the reason he asked the question, again, I believe you can do better.

http://www.realguns.com/articles/314.htm

F. Guffey

Then there is my quote: That no one quotes, if they did they would have to ask “HOW?” Not an attempt to drive any anyone into the curb but I modify go-gages into go to infinity gages, something like a variable length head space gage. “A machinist (gunsmith) is only as good as his tools”, I believe it is more about what the operator of the machine does with the the tools.
 
F. Guffey said:
I have no infatuation with head space gages, there are only three between .000 and .016”+, there are no chamber length gages on the .000-(negitive) side. I make chamber length gages from .012 shorter than minimum length/full length to .016+, that is 28 different length.
Click to expand...

I have no infatuation with gauges either, but I do have them in 0.001" steps from the typical 1.630" "go" to the 1.638" "field" gauge for the 308 family of cartridges that I do more chambering for than almost any other family.
I made a "gauge protrusion" micrometer with a micrometer head.
It is zeroed on a granite plate and then allows you to measure how far a headspace gauge protrudes from the barrels torque shoulder,
This same exact measurement can be achieved by measuring to the bolt face from the receiver front ring and adding the thickness of the lug.

It is a very reliable way to work, and combined with a Ptg micrometer adjustable reamer stop, also a very easy and accurate way to work.
I can reliably work under 0.001" levels of chamber depth precision when chambering a barrel.
I would not trust using the depth feature of a set of 6" dial calipers to be as accurate/repeatable as my setup.
 
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