Measuring shoulder bump

[Posit]

How to measure the amount of shoulder bump when resizing brass? I've been measuring from base to datum line, because I have the tools to measure those points, but realized I don't know that is necessarily accurate. I've been assuming the die presses on the shoulder of the case, so pressing the shoulder moves the brass below below an equal amount... ?

 

[taxman]

Hi Posit,

Read through the following link. I was having issues with a 243 IMP cartridge.

http://www.websitetoolbox.com/tool/post/6mmbr/vpost?id=2770621
I am stumped and need help under realoading forum,All calibers)

The guys on this forum explained in detail headspace, bumping the shoulder and how to measure it.

Thanks,
Tony

 

[Posit]

That was a great thread, with a lot of good input... but at this point, I simply want to accurately measure the amount I am bumping the shoulder; .001 or .002 is pretty tiny to my uncalibrated eyeball. I did see the reference to "Stoney Point head and shoulders tool which Hornady now calls the Lock and Load Headspace gauge kit"; is that the only or best method of getting an accurate measurement??

 

[spclark]

The Stoney Pointe / Lock'n'Load tools are intended to measure to the shoulder datum line, if you're using the proper gauge insert for the cases you're measuring.

That being said, your method is what 98% of us do for bumping shoulder back,I won't comment on the other 2%) as long as you're doing it for a bolt gun. Gas guns tend to operate better / safer with more of a bump, as well as full-length resizing between firings, but you probably know that already....

 

[AckleymanII]

I use a Davidson ogive gage of a larger caliber available from WWW.sinclairintl.com

I may use a 30 cal on a 243
270 on 223
33 on 7mm
35 on 30 cal

good luck!

 

[tenring]

This is the same question I asked on BR Central few days ago. You may be interested in the responses:

http://benchrest.com/forums/showthread.php?t=55245

Its very frustrating to measure .001 bump with the tools out there today.

 

[Atomic_Cowboy]

Will the Hornady Lock-N-Load Headspace Gage work with 40-degree ackley shoulder?

Thanks,
DG

 

[tuck2]

Take a look at the Redding Competition Shellholder Set that they started selling this year. There are five shellholders that increase in .002" incrememts. You can use the shellhlders to set the case headspace to fit the rifle chamber.

 

[Posit]

tenring: I read the posts on benchrest.com; your Harrel's "thingy"... and your conclusion that there isn't a good tool out ther to accurately measure shoulder bump.

I don't know what/how the Harrel's "thingy" measures, but kind of sounds like measuring the length of the case from base to datum line is the most reliable, consistent method reasonably available. And that's probably OK, rifle by rifle; just won't give an actual/comparable measurement.

Thanks for the input--

 

[BoydAllen]

I have the Stoney Point tool, and the brass tool that Lynwood Harrell furnishes with his dies. The latter is somewhat caliber specific, being limited to the PPC and BR cases, 6mm and less, after fire forming,if made from .220 Russian brass), with the standard shoulder angle. The Stoney Point tool should work with any shoulder angle.

The key to getting good readings with either is to apply light pressure to the case being measured with the adjustment wheel of the caliper while shifting the base of the case around on the movable jaw of the caliper with the thumb and forefinger of your other hand. With a little practice, you should get the feel of it. Look for the smallest reading that you can get, without deflecting the jaws, for each case.

If cases are not from the same lot, fired and sized the same number of times, they will likely have different amounts of spring back, which will result in variations bump that a given die setting will produce. Uniform lube application and having a shell holder that gives a positive stop against the die will also help.

If one is talking about getting consistent repeated measurements of the same case, the "problem" is a mystery to me, since I have an easy time achieving consistent readings with either tool. If, on the other hand, the problem is getting consistent bump, from case too case, the factors mentioned above may dictate a slightly greater average bump, so that the hardest cases' shoulders are bumped.

In short range,1-200 yd.)Benchrest competition, where the same small batch of cases are usually used all weekend, it is common to have to readjust FL dies as brass work hardens from repeated sizings and firings. Because of this, I measure the bump of the first case sized, when reloading a particular set of cases, each time that I load them, to make sure that my die setting is producing the bump that I want. This measurement is done with a barrel stub that has the front of the chamber reamed in one end. I only use it with brass from chambers reamed with my reamer, since I have learned that chambers of the same nominal neck diameter,.262) man be slightly larger than mine, which can cause the stub to take a false reading off of the base of the neck,where the bushing doesn't size due to its chamfer), rather than the shoulder.

 

[AckleymanII]

Boyd, the Davidson Ogive gages works as well as a "neck checker" and is a whole lot easier to handle since it is attached to your dial caliper.

 

[tenring]

posit - Measuring from base to datum line within .001 is extremely difficult. You gotta hit exactly in center of datum line every time. The Harrel's "thingy" is a small brass cup with hole at the top and beveled 30 degree lip at the bottom, for 6ppc and 6br only. It sits upside down over the shoulder and with caliper, is used to measure shoulder set back. Problem is multiple measurements on the same fired case are seldom identical.

Keith - I have most the Davidson ogive guages. How are you using them to check bump???

 

[Posit]

After the comments/input received, believe my question has changed somewhat. I use the Stoney Point tool, and am, theoretically, at least measuring to the datum line,approximately). I get pretty consistent measurements on a given case. So, seems to me, that if I set my body die to a measurement at that point, all other cases will "bump" to that setting, and the shoulders of all cases will be the same. This does not give a precise measurement to the actual shoulder of the case, but will provide a consistent length,even if I can't measure it). Thus, if I have a tight case and "bump" .0002 based on whe measurement I get with the tool, I am also bumping the shoulder back the same amount and the case should chamber easily. Yes?

 

[rayjay]

Yes.

This is not rocket science. Practice with whatever tool you are using so you can be consistent. Adj your dies so that you are bumping back .0005 to .002. Check a case every now and then. Write the fired and sized dimensions down in your notebook every loading session.

Once you get used to measuring the shoulder you will have a hard time adjusting a sizing die without double checking the bump. It's peace of mind for a critical part of reloading. I make up Harrell's style bushings for any new cartridge I get [ actually it's any new shoulder angle, I just had to make up one for my 6mm Beggs ].

 

[AckleymanII]

tenring, bumping back the shoulders .001-.002 or less is no big deal. Most guys want to over think this.

I made a post earlier on page one on how I use the Davidson Ogive gages. I have been using these since the mid 80's.

I used to have Neck Checkers made with the reamer that cut the chamber on a barrel stub, but it is easier to use the over size ogive gages that only cost $12 each.