Comparator gauge

[spife7980]

JBO, If you drink I suggest you stop, if you do not drink I do not suggest you start, I believe you are silly enough sober. And then I wonder; where is your pride, self respect and dignity.

F. Guffey

And likewise we all wonder where your pride, self respect and dignity are.

Sure people are incorrectly referring to the comparators as head space gauges which, yes, technically they are not. BUT that is the common vernacular and they do allow you to measure relatives. If my fired case shoulders measure 2.000 and after sizing they measure 1.998 then what do we have? Thats right, the shoulders are .002 shorter than a fired case. Also known as bumping them back .002. It really is that simple. Sure an absolute measurement to the .04 shoulder datum line may be a different measurement but what the hell difference does that matter? We interested in a before and after for our individual set ups.

 

[Alex Wheeler]

An exact measurement at the datum is no more useful than a measurement at any other point on the shoulder. Chamber shoulder angles do not match the die shoulder angle perfectly, even if they did the spring back after sizing will not be exactly the same across the whole shoulder. To find how much clearance you have between a sized case and YOUR chamber your shoulder comparator must be made with the reamer the chamber was cut with, or you size the case to get a "zero feel" on the stripped bolt and record the measurement, then sized more from there. You may need to see a reading of .004" setback with your particular tool to actually end up with .002" clearance in your chamber. We need not be concerned with the datum.

 

[Patch700]

An exact measurement at the datum is no more useful than a measurement at any other point on the shoulder. Chamber shoulder angles do not match the die shoulder angle perfectly, even if they did the spring back after sizing will not be exactly the same across the whole shoulder. To find how much clearance you have between a sized case and YOUR chamber your shoulder comparator must be made with the reamer the chamber was cut with, or you size the case to get a "zero feel" on the stripped bolt and record the measurement, then sized more from there. You may need to see a reading of .004" setback with your particular tool to actually end up with .002" clearance in your chamber. We need not be concerned with the datum.

All fine and dandy... But what if its a 30-06 case we are dealing with?? AND I would like a little air between the case and the chamber??? Preferably clean air but hey beggars can't be choosers..
To add to this conundrum, I am unable to cram enough feeler gauges (from harbour freight no less) in between the case and the shell holder to attain this said "air gap" .. It's almost as though my press is being "Wupped" be my brass?
The only reason I ask is because as of late I have been informed that "I" (me) cannot bump shoulders back and as if THAT wasn't bad enough , I have no clue why.. In closing, is this gap of clean air going to be a close match between my chamber and aforementioned brass by doing it in the way you've described?


Signed : The guy who formerly bumped shoulders but now is unsure.

 

[Alex Wheeler]

If you cant bump your shoulder, cut off the bottom of the die.

 

[Texas10]

If you cant bump your shoulder, cut off the bottom of the die.

Or...go back and put a little more headspace (oh God, I've said it again) in your chamber. I'd set my headspace a little tight on the go gage, and my dies could not size my brass short enough, so instead of grinding the die, I re-set the headspace.

And then I started thinking about how that effects case capacity, and.... oh well, that's an entirely different argument.

 

[WANTASHOOT]

Sorry I have not been more involved in my question. I have been busy at work.

What I found was that if I used a comparator with a small hole and measured at the top of the shoulder (near the neck) I had to bump the shoulder about .008 before my bolt would close the way Alex Wheeler describes in his video.

Now if I use a gauge that has a larger hole and measure right by the shoulder to case junction I am only moving that part of the shoulder .002 when the bolt closes per the Video

Alex this is a Redding die.

it seems the die/chamber have a slightly different angle which is causing this. Or maybe it's nothing to worry about?

 

[fguffey]

Or...go back and put a little more headspace (oh God, I've said it again) in your chamber. I'd set my headspace a little tight on the go gage, and my dies could not size my brass short enough, so instead of grinding the die, I re-set the headspace.

I have never found it necessary to grind the top of the shell holder or bottom of the die. I form cases for short chambers, when forming cases for short chambers I raise the case off of the deck of the shell holder with a feeler gage. The RCBS shell holder is my favorite because it does not fit, correction; the RCBS shell holder fits like a hand-me-down shirt, it fits where it touches.

Another advantage to raising the case off of the deck of the shell holder; there are many times a reloader allows the case to whip their press meaning the case has more resistance to sizing than the press can overcome. When that happens I raise the case head off of the deck of the shell holder with a feeler gage. I believe I am the only reloader that checks to determine the winner; the case or my press. When determining the winner I check the gap between the bottom of the die and top of the shell holder, if the case won there will be a gap. Anyhow; that is the reason I have never found it necessary to grind the top of the shell holder or bottom of the die.

F. Guffey

 

[fguffey]

it seems the die/chamber have a slightly different angle which is causing this. Or maybe it's nothing to worry about?

Weatherby chambers are like that, Weatherby was the fan of the radius. And then there was the big inning. In the big inning and that would be before SAAMI the length of the chamber was not listed from the datum to the case head; it was listed from the case body/shoulder juncture to the case head.

I am the only reloader that is not infatuated with 'the datum', I make datums, I collect datums etc. but when using a comparator I am not particulate about the diameter of the datum. I know, reloaders have been trying to match SAAMI to Hornady/Sinclair measurements, I don't, They have made an attempt to make their comparators case friendly and reloaders have never learned the value of verifying.

When determining if the chamber has a radius at the case body shoulder/shoulder juncture or the shoulder/neck juncture I make a visual check.

F. Guffey

 

[ireload2]

Weatherby chambers are like that, Weatherby was the fan of the radius. And then there was the big inning. In the big inning and that would be before SAAMI the length of the chamber was not listed from the datum to the case head; it was listed from the case body/shoulder juncture to the case head.

I am the only reloader that is not infatuated with 'the datum', I make datums, I collect datums etc. but when using a comparator I am not particulate about the diameter of the datum. I know, reloaders have been trying to match SAAMI to Hornady/Sinclair measurements, I don't, They have made an attempt to make their comparators case friendly and reloaders have never learned the value of verifying.

When determining if the chamber has a radius at the case body shoulder/shoulder juncture or the shoulder/neck juncture I make a visual check.

F. Guffey

 

[Alex Wheeler]

Sorry I have not been more involved in my question. I have been busy at work.

What I found was that if I used a comparator with a small hole and measured at the top of the shoulder (near the neck) I had to bump the shoulder about .008 before my bolt would close the way Alex Wheeler describes in his video.

Now if I use a gauge that has a larger hole and measure right by the shoulder to case junction I am only moving that part of the shoulder .002 when the bolt closes per the Video

Alex this is a Redding die.

it seems the die/chamber have a slightly different angle which is causing this. Or maybe it's nothing to worry about?

How is accuracy and brass life? These are the kind of things we deal with because of different manufacturers and production tolerances. Is it ideal? No, but I think you'll be just fine.

 

[Northridge]

Datum not at all important to bump cases. Tom Mousel you have two left hands how could you ever figure a datum point Lol...

 

[BoydAllen]

Just for one more data point, on a PPC when I bump case shoulders .001 using the brass gauge that Harrell's furnishes my bolt closes just fine. I like that style of gauge, simple and reliable.

The other shoe on this subject is that you should always measure the diameters of the bodies of fired and sized cases to make sure that your die is small enough for your chamber. I prefer just above the extractor groove where you can see the end of the sizing die contact, and at the shoulder. I have run into a couple of cases where a match chamber and a factory die did not work properly. Setting a die by any feel method alone in this situation will have the shoulder too far back when the bolt feel is right, and that will eventually lead to a case separation. Measure the case before and after, use a gauge/comparitor, and if it takes too much bump to get the feel you want, you need another die. Here is the link to another of Alex's excellent videos that explains about measuring cases.