Shoulder Bump?? I might be a bit "DIM"!

[Bitis Arietans]

So...I feel like an idiot!

When you "just" make contact with the shell holder and the FL Sizing Die

vs.

"tighten down" the die, say a 1/4 turn (Cam-Over"?) you get more "bump"

In other words, sort of, push back the shoulder (datum point)

The way I understand the "perfect" situation, for best accuracy...You need to screw down the die, to maybe just touching the shell holder...test the round in the rifle, if it's "snug", closing the bolt, screw it down "just a bit more", for it to chamber....

and that's the sizing that's perfect!!??

 

[bigedp51]

Chambers and dies vary in size so the best way is to measure a fired case with a Hornady cartridge case headspace gauge and adjust the die to bump the shoulder back the required amount.

Below on a bolt action you would bump the shoulder back .001 to .002 below the red dotted line. If you adjust the die as per the instructions you would push the shoulder back to the green dotted line. Bottom line you adjust the die for the minimum amount of sizing where the cartridge chambers and extracts reliably.

 

[Bitis Arietans]

I think I have it!

Can you actually measure the "new" bump?

Or just get a comparative, when using the Hornady Headspace tool.?

TY Ed.

 

[bigedp51]

I think I have it!

Can you actually measure the "new" bump?

Or just get a comparative, when using the Hornady Headspace tool.?

TY Ed.

Below is a fired .223/5.56 case in my Hornady gauge from my AR15 carbine. I adjusted the die to bump the shoulder .003 confirming the shoulder bump by measuring the case after sizing.

Many fired cases will not fit in a Wilson type case gauge so you do not have a starting point for adjusting your dies. The Hornady gauge fixes this problem by giving a before and after sizing measurement.

 

[Bitis Arietans]

So..Screw the die down/up in the press, and measure the before and after?

You say... I adjusted the die to bump the shoulder .003

How do you adjust the die to that specific measurement? ..or is it a trial and error by moving the die up/down in the press/ And measuring the result?

Thanks again.

 

[tbrice23]

I personally deprime a fired round ,measure with the comparator. Then screw the die down until I can measure a .002" bump. Sometimes a fired primer will have slight cratering (raised points around the firing pin impact ,that will throw off your initial measurement).

Hint,
The .002" bump will coincide with the point where your bolt will just close nice on your sized brass. so if you don't have the Hornady H.S. comparator your bolt close effort will tell you when you've sized just enough. Just keep sizing down an eighth of a turn at a time till the case chambers. And try a few other sized pieces to verify before locking your die ring.

 

[bigedp51]

So..Screw the die down/up in the press, and measure the before and after?

You say... I adjusted the die to bump the shoulder .003

How do you adjust the die to that specific measurement? ..or is it a trial and error by moving the die up/down in the press/ And measuring the result?

Thanks again.

I use Redding competition shell holders, once the die is setup it is never adjusted again and you change shell holders to adjust shoulder bump.

REDDING COMPETITION SHELLHOLDER SETS | Sinclair Intl

Redding's five piece shellholder set is designed so you can adjust your headspace by selecting the appropriate thickness Redding shellholder. The five shellholders are +.002", +.004", +.006", +.008", and +.010" thicker than normal shellholders (.125" from the bottom of the case head cut to the top of the shellholder). Each shellholder is clearly marked and has a black oxide finish to distinguish them from normal shellholders. Comes packaged in a 6 position storage box leaving an empty space for your regular shellholder.