A question about bumping the shoulder?

[Scottf]

Check out Dave Manson's cartridge comparitor, come with 4 gage blocks to cover the majority common cases. Very easy to set up and use.
https://mansonreamers.files.wordpress.com/2019/08/january-2019-catalog-1.pdf

 

[MagnumManiac]

This is only important when comparing measurements from other folks. As long as you're internally consistent, and are somewhere near the middle of the shoulder, you can compare fired and sized brass with a variety of methods. The only important measurement is the difference in length from the cartridge base to the midpoint of the shoulder of a fired brass, before and after sizing. This is why the "pistol brass trick" mentioned above is viable. I have the Hornady bullet comparator set, and just use whichever insert is appropriate for the caliber I'm measuring

First off, what's important to you is NOT important to everyone.

The datum IS important, it is the ONLY dimension to use for HEADSPACE.

Whether you are comparing to others or not is moot.

If you want to use a cartridge case to measure from, that's fine, but you must understand that that is not the Datum it is measuring from.
When you measure from a different point to compare bump, do you REALLY know what actual headspace you have?
Have you ever compared the 2 measurements side by side?
I know I have and you would be surprised by the difference.

Which really is head clearance we are measuring, not headspace.

Cheers.

 

[ShtrRdy]

You are a clever fellow. I'm feeling a bit like a doofus for not thinking of this nifty trick myself. Have you devised a means to attach it to you caliper blade, or do you just hold it in places with your fingers while taking a measurement ?

Thank you Sir. I just hold it vertically and "eye ball" it to see that it's basically centered.

There's a lot of talk here about this not being the datum. That may very well be for the cartridge being discussed. However there are many cartridges which have the datum on the shoulder where the diameter is 0.4". That's the same as a .40 S&W case.

 

[nicholasjohn]

First off, what's important to you is NOT important to everyone.

The datum IS important, it is the ONLY dimension to use for HEADSPACE.

Whether you are comparing to others or not is moot.

If you want to use a cartridge case to measure from, that's fine, but you must understand that that is not the Datum it is measuring from.
When you measure from a different point to compare bump, do you REALLY know what actual headspace you have?
Have you ever compared the 2 measurements side by side?
I know I have and you would be surprised by the difference.

Which really is head clearance we are measuring, not headspace.

Cheers.

If a guy wants some numbers to compare to SAAMI specs, he would have to measure at the correct place along the slope of the case shoulder. There is only one spot where the measurement can be correctly made, and the comparator tool will measure at the correct spot. On the other hand, If all the guy is looking for is to have a measurement of how far his resizing die has pushed the shoulder back relative to its location on his fire-formed brass, the pistol cartridge case method would provide that. He will know that his die has bumped the shoulder back "X" number of thousandths, but that's about all he will know. If he wants before & after numbers, these numbers will not mean anything relative to SAAMI headspace specs. Only the numbers derived from using the tool that measures at the correct spot along the shoulder will do that.

I don't feel a need to know absolute numbers in this situation. Some people do. That's why they make these special tools, and some people have developed handy tricks to improvise. I think we're talking personal preference here, and everybody get to pick which way he likes it. The only disadvantage I can see to using the pistol case method is that it would be easily damaged if it got dropped on the floor and had a flat spot along the case mouth. This wouldn't happen with the comparator tool. Since I already have the comparator, I plan to keep using it and have all the bases covered.

 

[Remmy700]

This is getting way to complicated right now

 

[nicholasjohn]

This is getting way to complicated right now

Yes, Sir - it is. It really doesn't need to b, either.

 

[entoptics]

This is getting way to complicated right now

Yes, Sir - it is. It really doesn't need to b, either.

Come on guys. It's just as complicated as the OP is willing to go.

For all practical purposes, "shoulder bump", is the difference between where your brass fire forms to the chamber's shoulder, and where your dies mash the brass back.

...The datum IS important, it is the ONLY dimension to use for HEADSPACE...When you measure from a different point to compare bump, do you REALLY know what actual headspace you have?

It absolutely IS headspace, at least as commonly defined in the reloading community.

"Proper Headspace", for all intents and purposes, is the distance a piece of brass can expand safely upon firing, without rupturing/weakening due to stretching and thinning.

A once fired piece of brass approximates the chamber dimensions (with OAL fixed at the bolt face). When you mash that piece of brass through a sizing die, it shrinks a certain amount. The difference is the "head space". The same can be said for factory ammo. If the factory ammo is shorter than the chamber by 0.010", then for all practical purposes, the headspace is 0.010".

Go, No-Go, and Field gauges are simply a way to conveniently test reference values for this distance for various cartridges. If it was some rule, defined by a datum, then there would be no such thing as wildcats. There'd be no threads on forums discussing how to go about setting a proper shoulder bump.

Each chamber is different by a few thousandths.

Comparators can't be much more accurate than that?

If you want to check all the boxes as a reloader, measure your rifle with tools you have, then do your best to make brass that fits that rifle.

 

[WildBillG]

So if I use a socket or 40 S&W case I can find out if I bumped shoulder .002 of an inch. FOR THIS MEASUREMENT DO i really need to be on the shoulder or just some where between the neck and shoulder? I ask this because our die should be similar in shape to our brass correct.

 

[Orange Dust]

Correct. Sammi is irrelevant unless you are loading commercial, or more than one gun then you would full length size with small base dies. You want your brass to fit closely as possible to minimize working the brass and for max case life. Folks are trying to overcomplicate. When setting the sie only size a case once. If you miss try another fired case. After you are happy with the setting, run the test ones back through. Only reason for this is to get ammo that will always function and max case life and accuracy.

 

[WildBillG]

Thank you Orange Dust that helps I understand what others are trying to say and in some cases may be needed but not for only one gun aand a slight bump.

 

[Orange Dust]

Thank you Orange Dust that helps I understand what others are trying to say and in some cases may be needed but not for only one gun aand a slight bump.

Exactly. Dont overthink.

 

[entoptics]

Thank you Orange Dust that helps I understand what others are trying to say and in some cases may be needed but not for only one gun aand a slight bump.

I will add, that getting a consistent bump can be harder than it seems. You may need to take some material off the top of your shell holder, as the cam-over on your press may be tight enough to give inconsistent results.

I had this problem, and was getting variation of over 0.004". For 270 and 30-06 I sanded my shell holder down about 0.005". It still bumps the die when it's properly set, but not nearly as much. This improved my sizing precision to about 0.001".

I used a lathe at work to do the same for my 300WM, which also improved consistency.

It's also important to consistently lube your cases of course.

 

[robert l]

I think im missing some thing here. If you use a fl sizing die for bumping the shoulder back Then the case would have to go pretty much to full length to push the shoulder back? Or are we saying to 90 percent the way down the case and then check? Now i know every chamber is different. So you are pretty much resizing the whole case?

 

[Orange Dust]

Yes unless you are doing it with a bump die.