General case length and trimming questions

[F. Guffey]

last time I looked a measurement is a line, and measurements are what I use when I reload. Not 1940 gun shop slang

I suggest you push yourself away from the keyboard, after you figure how to do that try to come up with there different ways to measure the length of the chamber from the shoulder to the bolt face without a head space gage.

And I will guarantee you will not find gun slang that goes back to the 40s, there was an incident. there were smiths that did not understand what another smith was doing and they did not know how he was doing 'it'. So they bad mouthed him, it is no wonder he did not respect them.

F. Guffey

[hounddawg]

I suggest you push yourself away from the keyboard, after you figure how to do that try to come up with there different ways to measure the length of the chamber from the shoulder to the bolt face without a head space gage.

Why? I only need to know how one way to do it as long as that method is precise. All I care about is tracking barrel erosion and getting consistent ammo. My results are all I need to know that the method I use works. I am not a benchrest shooter either BTW

[cw308]

Guff
We all know what is ment when where talking yes headspace , datum and ogive settings . I enjoy reading your posts but this is getting old . You can correct me everytime and even though your way of thinking may be right , most know what I'm talking about . I try to keep things simple on a high school level. Sorry.

Chris

[Unclenick]

Datum is the singular form of data. A datum is a defined reference location from which other measurements are taken. The idea is that by taking all measurements directly from a datum rather than taking them in turn from other measurements taken from the datum, you avoid accumulating tolerance error.

An Example: When a millwright refigures a milling machine, he picks a point, usually on the vertical knee way, from which you can indicate and measure everything that needs to be parallel or square or perpendicular to it without incurring cumulative tolerance error. That point is a datum. But note here, the millwright figuring the machine gets to choose that datum where he finds it to be convenient to work from. So can you "make" a datum? Yes, by choosing the reference location for yourself. For a cartridge case, does it have to be the same datum SAAMI has chosen? No. Indeed, look at CIP drawings of the same cartridges and you see they assign no shoulder datum at all. Providing a specified shoulder datum is strictly a SAAMI convention for taking off other measurement values from it. For a handloader, as long as he is consistent, he can measure from wherever he chooses to place the shoulder datum on the case and chamber shoulders, just like the millwright can make a choice, and adjust his measurements accordingly.

To be able to find your own datum or SAAMI's on an actual case or in a chamber, you need a datum gauge or reference. You can drill and ream a cylinder of any material that won't warp or deform in use to serve as this datum locator for a case and turn a rod to the diameter of the chosen datum to locate it in the chamber. If the terms datum gauge or datum reference or datum finder are shortened to just the first word, I don't see the harm in that unless it confuses someone. The point is to find where measurements are to be taken from and it will do that.

Another example:

Originally Posted by hounddawg

What I was saying is regardless whether you are seating from from the metplat of the bullet or the ogive datum the measurement is based on the distance to the case head.

There is no official ogive datum value from SAAMI. The bullet comparators we use from Hornady and Sinclair do not have the same hold diameters for the same bullet calibers. Yet, we do take measurements from them so they serve as a datum, just one for which no official specification exists.

And yes, it is standard practice to measure from someplace on the bullet to the case head, but because the case shoulder determines when the case and bullet stop getting closer to the throat, that distance can only indicate how consistent bullet jump is within the limit of how consistently the shoulder datum to head distance has been resized and gives no number, it is not direct. So my gauge does not use the head at all, but rather rests on the case shoulder with a shoulder profile cut with a chamber reamer and measures to the bullet ogive where it contacts the actual throat profile as cut by that same reamer to make the controlling surface and distance measurement directly. I first use the Hornady Overall Length Gauge to find the throat of my actual chamber, then measure the gauge's "cartridge" with its bullet out at contact distance to zero my gauge. After that, it reads bullet jump directly as the number of thousandths away from the zero it is. In the photo below it is a jump of about 20 thousandths. If I had used a digital indicator I could zero, the jump would be a minus number.

[hounddawg]

I just don't see the need to over complicate what is nothing more than a simple straight line measurement.

if you goal is to make your ammo consistent it is not a had task. A few simple tools and straight forward measurements is all that is required.

[F. Guffey]

To be able to find your own datum or SAAMI's on an actual case or in a chamber, you need a datum gauge or reference. You can drill and ream a cylinder of any material that won't warp or deform in use to serve as this datum locator for a case and turn a rod to the diameter of the chosen datum to locate it in the chamber. If the terms datum gauge or datum reference or datum finder are shortened to just the first word, I don't see the harm in that unless it confuses someone. The point is to find where measurements are to be taken from and it will do that.

Or a reloader can make up a datum. after that? Use the 'personalized' datum with their own personalized comparator. L. Willis declared he made a digital head space gage, reloaders swooned over it. I recognized his tool as a dial indicator stand but to reloaders thought it was another way to make a head space gage but first someone had to get SAAMI to change their chamber drawings by adding the symbol for head space to the drawing. Anyhow; the case does not have head space.

Gun Smith Slang: In 1938 Wilson case gage starting selling the L.E. Wilson Case gage complete with instructions. Owning the gage allowed reloaders to use their thumb nail to check protrusion, most did not understand what it meant when the case protruded; ME? If it protrudes I can measure the protrusion thousandths. If it does not protrude still not a problem because I can measure depth also in thousandths.

And then there is the very few that understand the Wilson case gage is a datum based tool. The first Wilson case gage I owned risk giving its life for my education. In an effort to avoid that I took a lubed case and placed it into the Wilson case gage. I had no interest in the case being an 'innie' or an 'outtie' all I wanted to do was imprint the gage.

I placed the gage on a block of lead and then drove the case into the gage until the case head was .200" +/- below go-gage length, I then drove the case from the case gage.

All I wanted to know was; "What did the datum look like?" The datum on the Wilson case gage has a radius, I thought that was brilliant because Sinclair and or Hornady has not been able to make a gage that is more than a comparator. The Wilson case gage can be verified in more than one way.

I guess smiths in the 40 skipped the '30s and started all of that slang.

F. Guffey

[hounddawg]

All I wanted to know was; "What did the datum look like?"

Guffy I see you still think a datum as a physical object. You just can't get past your slang and learn that a datum is nothing more than a reference point used to take a measurement. This old dawg can learn new tricks, some can't

[F. Guffey]

This old dawg can learn new tricks, some can't

And then there are old dawgs that are widely indignant about everything. All Capp was surrounded by students, I am sure the students took pride in being hard headed and indignant. POINT? All Cap gave them a name, he called them 'SWIANE' and then they got more indignant.

They caught up with him during summer break in Florida, he was not difficult to find.

They surrounded him and wanted to know why he called them swiane.

And then there are shooters instead of students and as the man said in finance it is easy to change indigent to ignorant as in 'not knowing'.

If I want a datum I make a datum, again I was at a gun show when I looked at a box of tools and said 'DATUMS!".

The dealer said he did not have any datums, the shopper in front of me ask "WHERE?" and the shopper behind me ask "What does a datum look like?"

Back to the Wilson case gage, the radius on the datum was at .375" for the 30/06 case gage. The Sinclair and Hornady gage has a radius, it has taken years to get reloaders to understand they have to verify the comparator if the datum has a radius. And then there are those old dawgs that do not understand the datum is not a line.

I was not trying to win a popularity contest. but there were people treating people rather rudely, so I created a contest. One student ask me about restrictions like 'where can he go to get help?' No limits anywhere and everywhere, anybody or everybody. The student that had the most interest reminded me the riddle was never solved and those rude people are saying ugly thing about me. I solved the riddle in about one minute and handed it to him.

His feet hardly hit the floor before he reminded them they said it could not be done. He was rough on them.

F. Guffey

[hounddawg]

believe whatever you want Guffy and rest assured you are the only one who uses that term the way you do.

[F. Guffey]

believe whatever you want Guffy and rest assured you are the only one who uses that term the way you do.

I do not use 'the term' I use 'the datum' I make tools that include 'the datum' without the datum the tool is unless.

Reminds me of a reloader trying to bump the shoulder back, the reloader is convinced he is doing something, he just does not know what. ME? not a problem, I find it impossible to move the shoulder back with a die that case body support.

F. Guffey

[Unclenick]

Originally Posted by houndawg

I just don't see the need to over complicate what is nothing more than a simple straight line measurement.

Under-complicate. You may be missing that I am eliminating one source of cumulative tolerance error with a single reading, something that requires two separate measurements and a calculation to eliminate with current commercial tools. Maybe I've failed to communicate the object of the exercise adequately? It is to improve the precision with which I control bullet jump, keeping in mind the case-head-to-shoulder-datum dimension has some variation among cases coming out of the resizing die that becomes variation in bullet jump that is not accounted for with a single measurement by the current crop of commercial tools. I freely admit the error is typically small enough to be of unlikely significance to most loads. The error would only be a significant percent only of very tight jump values of a few thousandths.

Anyway, the datum argument has run its course, I think, and sides have been chosen. Probably time to think about closing this out. I'll leave it up for rebuttal for another day, then shut it down.

[hounddawg]

What's complicated about using a sized case with a split or lightly sized neck to get the datum to establish where my loaded round will be touching the lands. Benchresters been using this method for decades to get one hole groups

I think I answered the OPs question way back at the beginning of the thread. Trimmed case length has nothing at all to do with the rounds overall length when a bullet is seated

On datum argument I will always use the definition which every engineer in the world uses - A line which serves as a reference or base for the measurement of other quantities. You can't hold it , touch it or buy one at a gun show

[F. Guffey]

What's complicated about using a sized case with a split or lightly sized neck to get the datum to establish where my loaded round will be touching the lands.

I know what you are talking about, there were three of us that called those cases 'squid necks' because shredding the neck gave the case the appearance of being a squid, something like the Humboldt squid.

No one ever considered shredding the neck of the case because we used all of the bullet hold we could get. There was not one of us that practiced bad habits. With all of the bullet hold we could get we never had to start over the next day, we never had to worry about the bullet sticking into the lands.

AND we understood we were making transfers.

F. Guffey

[Metal god]

I understand completely and now am a bit sad . I never considered that aspect of measuring bullet jump . Thank god I use the Redding comp shell holders and my cases are pretty much sized all exactly the same from head to datum point on the shoulder . This should result in a rather consistent bullet jump to the lands for me .

How ever guys that allow there press/linkage to flex/deflect when sizing cases often have a head to datum point variance that can be as much as .004 to .007 from case to case . This means a 308 case that measures 1.629 from head to datum point will have the bullet ogive .005 closer to the lands when fired then a case measuring 1.624 head to datum if both cartridges bullets are seated the same length from head to bullet ogive .

Mind blown once again .

[RC20]

i

f you goal is to make your ammo consistent it is not a had task. A few simple tools and straight forward measurements is all that is required.

That is my take.

This is not like we are machining two separate surfaces and then hope they go together. Or an entire assembly, where stacking tolerance will cause problems at some point.

You measure the shoulder, you re-size, you check again. Did it move the desire amount? Yes: Into the keep bin. No, adjust and do again. Repeat until you are hitting in your range (mine is .002 to .,004)

With a bullet, the Ogive is already a wider tolerance than the tool that measures it.

You don't stack tolerances as you are measuring a single aspect of multiple items none of which fit together.

Each round is then "unique" . Its going to have a range of whatever the range of Ogive is (having found a few that were pretty wild outside the normal)

As nothing is solid, and its not like were are into diesel fuel injection system where tolerances are in the 10/thousandths, not an issue.

A too large a plunger bore and a too small plunger will indeed bite you there.

Or as we found out on a Volvo diesel, their solution to the tolerance issue between the sleeve and the piston was to sort them into relative groups.

So you had too large pistons and too large liners in one group

You had two small pistons and too small liners in another.

That is another way of making it non complicated. You could put a lot of money into more precision or you could just measure the end result and sort to suit.

Pretty practical solution.

And in the end, does .005 one way or the other make it not do what you want or does it not care because, gasp, we have another series of stacking issues with the barrel, the trigger, the shooters finger and the shooter and the sight and ........

[hounddawg]

RC20

I agree that there comes a point where we start to over think such things and any differences get lost in the noise of environment factors and shooter error.

Oh and Guffy I don't use the split case myself any more. I prefer sizing only the first few thousandths of the neck with a bushing die or doing a very light neck sizing using a collet die

Too tight a neck will give errors because the lands will dig into the bullet jacket or even into the core throwing the reading completely off. After chambering if there is any sort of groove in the bullet where it contacted, toss it and start over

I don't do this but if you want to get real anal pull the extractor before chambering

[Metal god]

While all that is true might point was , just when I thought I knew exactly where my bullet was in relation to the lands . It turns out I didn’t.

As for will it matter , I think we all have seen just about any one thing does not seem to be all that noticeable.

[hounddawg]

I always freak people out when I say I don't care about whether my reloading scale is accurate as long as it is precise. The key is in recognizing what worked then duplicating the measurements and weights then repeating it as precisely as possible.

[Dufus]

The thought that I have always gone with is making good hand loads involves eliminating variables. Thus building consistency.

We all have our perks and peeves, so we decide that one variable is not detrimental to my cause and others are.

I have been rolling my own for so long that I have determined what makes a difference to me and what does not.

This does not mean that I didn't use to be anal about everything, because I did, to the point that it became laborious at one point.

So, I stepped back, re-evaluated, and picked apart my procedures. Now I am a happy hobbyist that enjoys a lot more than I once did.

As always: whatever floats your boat. If it works for me, then screw what everyone else is saying.

[cw308]

When ever your headspace is less then zero , let's say you sizing with a .002 space from base to shoulder datum and you know your base to ogive , and your seating that bullet to a zero jump , with that .002 headspace sized case , once that firing pin drives the case to the chamber shoulder it jams the bullet to a .002 jam . I set my cases to .0015 - .002 and my seated bullet to a .002 jump.

[RC20]

I don't do this but if you want to get real anal pull the extractor before chambering

Guilty. I hated the yank and some evidence it can distort, so I size sans and use an M die to set the neck opening.

Minimum sizing as evidenced by a 2 to 4 thousandth shoulder setback. I use Lee rings on the dies so I can touch it back and forth a bit to fine tune. Works good.

As for bullet seating, I start 10 thousand off the lands and see what looks best then run it on out from there. I havn't found one that wants to be any closer (or is more accurate closer)

[hounddawg]

I do the Berger test with minimum load before doing the powder workup these days. Find the a good rough depth then find the powder load. I seem to get dialed in faster using that method

[F. Guffey]

As for bullet seating, I start 10 thousand off the lands and see what looks best then run it on out from there

.

How do you do that? I want to know the length of the chamber from the beginning of the rifling at the end of the throat to the bolt face. I must be the only reloader that does it 'complicated' way. Proof? Too many excuses by reloaders to do it 'the easier way'.

F. Guffey

Remove the extractor? I can only guess that is a rule because a bench rester said, "DO IT".

[hounddawg]

I must be the only reloader that does it 'complicated' way. Proof? Too many excuses by reloaders to do it 'the easier way'.

As long as it works for us does it matter? When installing barrels I use quality GO/NO GO gages to ensure the headspace is set accurately. Accuracy is necessary to do the job correctly. When reloading the goal is precision not accuracy. If all 50 rounds in that box are all as close to being identical as I can make them I am happy

If you don't understand the difference between accuracy and precision, I suggest you educate yourself.

[F. Guffey]

As long as it works for us does it matter? When installing barrels I use quality GO/NO GO gages to ensure the headspace is set accurately. Accuracy is necessary to do the job correctly. When reloading the goal is precision not accuracy. If all 50 rounds in that box are all as close to being identical as I can make them I am happy

If you don't understand the difference between accuracy and precision, I suggest you educate yourself.

The question was about determining the length of the chamber from the rifling at the end of the throat to the bolt face. I understand you can not help yourself but it appears you almost talked it to death.

I was wondering if RC20 could determine the distance from the rifling to the bolt face, do not get me wrong, I was impressed with that tid-bit about removing the extractor, there are rationales and reasons for removing the extractor I do not believe the reason "cause" is good enough. I go not believe, "because I have a bench rester friend and he told me to do it is a good reason.

F. Guffey