Shoulder Bumping & Case Head Clearence

[GW Staar]

Maybe I misunderstood him at first. (Probably)

Let me try again. Make your tool. Put the case in it. From THE OUTSIDE (this time) measure from the datum tool to the BASE of the case.

Still don't think it will work any better than my little tool. I may just not be getting my measurement from the correct datum line on the shoulder. It may be up or down from it., but it still works for me. Get a reading. Size the case until the shoulder is pushed back .001 or .003 or whatever one desires. Done.

Your method works the same as long as the shoulder you cut is the same angle as the chamber's angle and not cut too wide (possible only if the smaller bore for the neck is bigger than the datum diameter...and you wouldn't do that). It creates a datum (starting point) at the same point on the case shoulder as the chamber does. His method requires a diameter measurement at that point in the chamber. Yours requires drilling an accurate angle. Same thing in my opinion, except that if you don't have the tools to cut that same angle, his method works. Seems to me the datum point you measure from is the key...however you get it. I would love to have tools like yours and a space to use them....other than my company shop.

BTW, elaborating, the word datum, comes from the word data, and a datum is the point from which you start taking data.

 

[USSR]

Is that not the same as I do with the Sinclair Hex tool?

Yep, that's exactly what the Sinclair Hex Nut does.

Don

 

[JimKirk]

datum is the point from which you start taking data

It would be "ideal" if that point is the "actual" point of contact(POC) between the brass and the chamber.
That POC determines headspace on a "shouldered" case. The POC may be the entire length of the shoulder or it may be a thin .001 or so. That all depends on how good your brass and chamber match and really your sizing die too. We all know that there are manufacturing tolerances... right?

I know that some probably laugh when I mention marking the brass or smutting the brass, but really, that is one simple way to find the POC of your brass.

Jimmy K

 

[Walkalong]

Your method works the same as long as the shoulder you cut is the same angle as the chamber's angle and not cut too wide

I cut them at the SAMMI angle for the caliber. Now what the chamber is cut at, we can only hope.

I still use the Sinclair nut for getting a distance from the base of the case to the ogive of the bullet, but I like my little home made gauge for checking shoulder position.

 

[fguffey]

Datum again, not datum line, just datum, it is not simple, if it was we would not be having this conversation, for me? I use the companion tool to the press tool (the feeler gage) to change and or adjust the datum (point measurements are made from) when sizing cases.

I could drill a hole into my set up table that would be .375 in diameter and use the hole to determine the length of a case from the datum (top of my set up table) to the head of the case to determine the effect the case would have on head space, If I knew the length of the chamber from the datum/shoulder to the face of the bolt, again, I determine head space first.

http://www.z-hat.com/Cylinder.htm 30/06 cases that are 2.650 long from the head of the case to the mouth of the case and without a shoulder, just straight wall cases. This allows for the wildcatter, reloader, case formers and the few that determine the length of the chamber first first before firing in thousands.

OR I could fire a case THEN determine the length of the case from the datum (top of my set up table) to the head of the case THEN size the case and measure the length of the case from the datum to the head of the case to determine the amount of sizing.

A shoulder has varying diameters, the two angles of the shoulder form a cone, the point of intersection is called an apex, this is the reason I do not care what diameter the hole is used as long as I use the same hole when measuring, even if the hole has a radius.

A hole in my set up table turns the top of the table into THE DATUM LINE, but why, with two lathes, a mill.

One .375 hole serves as a datum for the 30/06, 7.7 Japanease", 25/06, 280, 270, 8/06 and can be used on any case that will not fall through the hole or a case that will fit through the hole.

F. Guffey

 

[fguffey]

Walkalong, you ask if you understood 'him' correctly, I am going to assume you were referring to me as him, AGAIN I did not say you could build it better, I never refer to SAMMY, Nothing I have matches his specs, he does not size my cases to fit my chamber, I do.

There is an outside chance someone reading this thread can say O I C.

If someone can drill and finish ream the hole to .375, they can make a datum, if they choose to cut an angle that matches the angle of a shoulder that works also BUT they have to understand there is no way to match SAM'S measurements as in from the DATUM (top of my set up table) to the head of the case, using the angle of the shoulder will be unique to the tool makers tool, but (as I tried to but failed) to explain if you could bore a hole to the correct diameter that would match SAM'S specifications on DATUMS you could measure the case from the datum to the head of the case and then look up SAM'S dimensions, again I do not have SAM'S chambers so all that information would be just NICE TO KNOW or something I could talk about but not something I use.

Again the effort on my part is made on the outside chance someone will come along that does not have their mind made up..

F. Guffey

 

[Walkalong]

True.

SAMMI only gives guidelines. "He" (Sam) does not know what your chambers actual measurements are.

Since I do not have the proper reamer, I can not make an exact .375 hole. I am sure I could get really close though.

Why .375, by the way?


"him".... Sorry, I should have said F Guffey

 

[GW Staar]

I Think .375 is arbitrary to a point. If you measure shoulder diameter at the exact center of the shoulder (between the smallest and largest diameters) according to SAMMI, it should measure .390. It appears he picked an appropriate number a little smaller than that...because he wanted too. Maybe smaller is insurance against a really loose chamber?
Like he said, it should work for any brass that won't fall through .375". .390" should work just as well in most cases....depends what bit you have that will bore bigger than the smallest shoulder meas. but smaller than the biggest shoulder meas.

What gets confusing to me is this: What if the shoulder angle in the chamber is a little bigger than the one on your tool? Then moving the shoulder of your brass back 2 thousands gauged on your tool, will move it back less in the chamber, and vica versa if the chamber angle is smaller....I think.

Is this why he's advocating two bores only, verses two bores and a angle reamer between? Oops, shoulda looked at your picture again, shoulda said, ....verses a bore and an angle reamer.

 

[Walkalong]

Not to mention the angle in the sizer die.

 

[fguffey]

Somewhere half way between here and there and in the center of the shoulder? That is the reason I believe most of this stuff is made up out of thin air, that would be a neat trick and every chamber mentioned, 30/06, 8/06, 280, 270, 25/06 7.7 would require it's own datum, as stated before all the chambers mentioned share the same datum (.375) plus many others.

.375 is the diameter of datum for the 30/06 because SAMMy says it is, I have no ambition to change it, as I have said before, I have 62 chamber reamers, cutting a shoulder for a case to sit against is not a problem, when cutting a chamber it is just as easy to take a few minutes to make a chamber gage out of a worn barrel, the only numbers to keep up with is case head protrusion AND the ability to measure protrusion from the barrel face and the face of the chamber gage to the case head,

Again, look at R. Lee's book on modern reloading by the same name, on each (most) of his case illustrations he took the time to list the diameter of the datum and the distance from it to the head of the case, I do it back wards, I determine the distance from the datum (shoulder) of the chamber to the face of the bolt first then adjust (transfer the measurement) the die to the shell holder in the press, after firing I can always determine the effect head space had on the case when fired, instead of firing first to determine the effect the chamber had on the case when fired.

My choice of cases: A case that is too long from the shoulder back to the head of the case to chamber, example 280 Remington, it's shoulder is forward of the 30/06, 8/06 338/06 35 Whelen, 270 Winchester etc. by .051 thousands. The 30/06 shoulder is head of the 8mm57, 7mm57, 275 Roberts, 308 Winchester etc. when forming cases there is no excuse for having head space in a chamber. When forming no one is required to fire the formed cases, when forming a reloader can determine head space by knowing when to quit moving the shoulder back.

Again we all know the shoulder is not moved back it is erased, part of the shoulder becomes part of the neck and part of the case body becomes part of the shoulder, I have never been able to get BUMP out of that description.

F. Guffey

 

[fguffey]

Advocating a bore? the only way to measure the distance from the datum to the head of the case is with a bore, the bore is not the same for all chambers/cases, the only way to check a go, no and beyond gage is with a bore, the bore (diameter of the datum) on the 30/06 is .375.

When I form and or size cases for my chambers I can make up the numbers, when WE all measure to one standard we must us one standard, it is only for us to understand everything below .375 is below the datum (table top), that leaves us with measuring everything that protrudes above the table top again the table top is the datum because the shoulder is an angle, we can use an angle BUT we will not agree nor will our measurements agree with SAMMY, unless we have a go-gage, then we can us it to check the measurements then what I could do (but will not), and that is to use a but grinder to lower the face of the tool until it agreed

To the die and shell holder, size a case, do not lower the ram, rotate the shell holder and remove it from the ram and case at the same time then remove the die from the press with the case installed, measure the case head protrusion from the die to the head of the case, the protrusion should be .125, if you have a head space gage for the 30/06 and place it into the sizer die it should protrude .130 in the perfect world because the go-gage is .005 longer from the datum/shoulder than a minimum length store bought commercial case from it's shoulder to the head of the case,

To get the case out of the die install it in the press, install the shell holder onto the case and ram at the same time and rotate, then, lower the ram.

And before placing the go-gage into the sizer die remove the neck expander/sizer ball assembly, first.

F. Guffey

 

[MCMXI]

My gunsmith makes up a bunch of "dummy" chambers that he cuts using the same reamer that he uses for the barrel. He gave me one for my .260 Rem the other day. Surely, that's the most accurate gauge to measure shoulder "bump" since the gauge and the actual chamber should be the same. Thus far, I've been doing it all by comparing fired cases to a SAAMI standard using Redding's Instant Indicator Case Comparator and have no complaints, but as fguffey and others have pointed out, this only works if the chamber of the rifle is cut to SAAMI specs or at the very least, close to SAAMI specs ... which hopefully it is.

 

[Walkalong]

Hopefully.

Many Benchrest shooters use bushing dies cut with the finishing reamer that the smith cut their chamber with. I have two of them from different smiths. One matches the barrel on the gun right now. They are all pretty close though, assuming the smith did a good job, which smiths who specialize in Benchrest guns do.

 

[Walkalong]

I bought a .35 Remington, so I needed another "gauge" to help set up my sizer. This time I tried fguffy's advice. (If I understood it right)

After drilling and then boring a hole to fit the neck, I bored a small amount to a larger diameter so it would hit in the middle of the shoulder, instead of cutting an angle to lay on the shoulder as on my previous gauges.

 

[JimKirk]

Back on the lathe again?

I like what you've done. I think that the single edge contact point will give a better read than the whole angled shoulder. Using the smut/marker "tool" I refer to from time to time, you can find that contact point, sometimes it is the whole shoulder, sometimes just a thin point. I have rifles that do both. It may be at SAMMI called for point or other points never know until you use the "tool". I drill pressed a "larger than the Sinclair Hex nut" right after the first date in this thread, works well too. All that is needed is a before and after measurement to know how much the shoulder has moved.

Jimmy K

 

[JimKirk]

I know this is an old thread ... but I also know that there have been a lot of new folks that have joined THR since then ... thought that a refreshing would not be bad ...

Walkalong ... I like the idea of holding the neck close to straight when measuring the shoulder .... that is something the Sinclair Hex Nut does not do... you just have to make sure the nut is making contact all the way around the shoulder ... but your idea would make it easier and faster...

The same idea could be applied to a bullet comparator.... the neck sized hole with the "ring" to contact the bullet at rifling diameter...

 

[Walkalong]

I have the Sinclair hex nut as well. It is a little harder to hold square and get a reading with, but as you know, it works. While it was intended to get readings off bullet ogives for checking jump to the lands, it works with brass shoulders to see how far you are sizing them as well.

So yea, my little gauges are a bit easier to use than the hex nut.