Shoulder bump ---***?

[chocdog]

Can some one please enlighten me on the following. I am new to reloading and have measured, sized, trimmed.... about 400 case of 30-06 cases.
Some were green but most were my own once fired brass.
I measured the base to shoulder 20 random once fired case with the LNL headspace kit and documented the length, took the average (2.040) and subtracted .002 and used that dimension (2.038) to set up my FL die. All the brass was sized and match the target length of 2.038". Casings chamber nicely.

Here's my problem. I load 50 of the above casings and headed out the range to for the first time this year. Everything went great.
Now I am getting ready to cycle them again. So I took more base to shoulder dimensions just to check everything out.
Now my measurements are 2.034 average vs 2.040 before That's 6 thou. How is that possible?
I even checked a few cases and they chamber as is.
My calipers are hardly use, never dropped and fresh batteries.
The Hornady bushing is aluminum, is it wearing out?
Should I still run the brass through the FL?
Totally lost and frustrated!:banghead:
Please explain?

 

[bigedp51]

Brass is soft and a GO feeler gauge is hard and doesn't change..............



Meaning you need a "base test" measurement that doesn't change to compare your readings.

Also the brass was fire formed to your chamber, so what moved your chamber or "how" you measured the case.

"97% of all errors are "human" errors and only 3% are actual mechanical failures"

 

[243winxb]

Now my measurements are 2.034

Before or after FL sizing??

 

[gamestalker]

Brass forms to the chamber. If the base to shoulder is measuring shorter than before, it is likely due to brass flow, being this brass is now taking on the characteristics of that chamber. It can very well, and likely will, shrink some where in it's dimensions, and grow longer in others during forming. It's when it has reached the point where it becomes difficult to chamber that shoulder bumping even comes into consideration. This is because new brass is sized to a one size fits all standard, and is smaller over all than most chambers of that cartridge. This is to ensure it will function in most all firearms chambered in that cartridge, this also means it is going to do quite a bit of stretching, and flowing, during the fire forming stage.

That brass will settle down, and your measurements will become far more consistent with what makes sense, and very likely within the next reloading or two.

And also considering the fact that some of that brass was new, and some was once fired of which you randomly sellected, your measurements are deffinitly going to be all over the place. Frankly I'm surprised your only seeing an unexplained variance of .006", in this respect.
GS

 

[Walkalong]

The simple answer is not only does the brass expand upon firing, trying to fill the chamber, it springs back some. After one firing your brass is not the size of your chamber. After three or four it is close. The brass gets springier upon multiple firings, but gets hammered clsoer to the chamber size as well. Kind of goes against each other.

Why do you think fguffey is always preaching about measuring chambers.

I use homemade gauges to measure where my brass's shoulder is after each firing and sizing. Do this for multiple firings in the same chamber and it will show you how much things can change. It will eventually give you a good idea of your chamber, and where you need to push the shoulder to.

Dead soft brass will size back easily, but as it work hardens, you will have to adjust the die down a little to keep the shoulder at the same place. If you have the sizer set for your brass with 15 firings on it, and then size a dead soft new case, you will push the shoulder back much farther than you want to.

 

[243winxb]

Annealing-Headspace

Very soft annealed brass can have the shoulder pushed back .010" to .014" from the strike of the firing pin. This i measured with a comparator. The overly soft brass was also below the lowest step of a L.E. Wilson case gage. If the primer fires, you would never know the head to datum line measurement has changed this much. Correctly annealed brass would not or should not, get the shoulder set back this much, when struck by the firing pin.

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[MEHavey]

First, relax... you're fine. No big deal.

The rest of this discussion referers to (what I assume is) a bolt gun.

2nd, I recommend you establish your case headspace dimension slightly differently. If your once-fired cases measuring 2.040" fits cleanly back into the chamber, that's your target dimension until you do step three.

3rd, Run the resizing die down until it meets the shellholder. Then back off a full turn. Size a case and see if it still chambers. (It's likely longer now because you squeezed its sizes in a bit.) If it still chambers, measure it and see if it is actually longer. If so, that's your new target headspace dimension pending step four.

4th, turn the sizing die in another 1/8 turn and resize. Check chambering... and headspace dimension again if it still fits. If longer, that's your new target headspace dimension pending step 5-10.

5th-whatever: Continue screwing the die down 1/8 turn at a time until either (a) the case quits chambering because the side squeeze finally lengthened it enough to where the shoulder is too long, or (b) the headspace actually starts getting shorter because the die is finally bumping it back. In either case, the longest headspace in all this that still chambered is your final target.

This reads longer than it is.... a few minutes at most, and you have established the headspace based against your rifle's actual chamber dimension regardless of firing springback.

 

[chocdog]

All set-up dimensions were taken from a random 20 from each lot of once fired brass, then averaged. Green brass was only measured after sizing.