Shoulder bump FL sizing and measurements

[Tac-O]

I've been using a FL sizing die on my 30 06 cases to just bump the shoulder back by 0.002 or so. I never did this by measurement initially, but did it by information I found that says if I compare a fired/unsized case to a FL sized case when chambering, there will be noticeablely more resistance when closing the bolt with the unsized case. Use this gauge for setting the sizing die to just bump the shoulders back. The instructions were to back the die out of the press until when sizing the case and then chambering that case, there would be slightly more resistance in the last 2/3 the way closing the bolt than the regular FL sized case.

I recently bought the Hornady bullet comparator kit for my calipers and added on the headspace gauge so that I could accurately measure the amount of sizing I'm doing.

So here's my conundrum. I took some fired cases and measured them with the headpsace gauge. From base of the case head to what I think is the datum line, a fired and unsized case measures 2.038 for my gun. After sizing it the way have been doing to bump the shoulders back, I measured again and got 2.040. So then I set up the die to the manufacturer's instructions to do a FL sizing, and once again the sized case measured 0.002 or 0.003 longer! On the next case, I set the die to where it only sized part of the neck and this time the sized case measured 0.0015 or 0.002 longer.


Why are my sized cases measuring longer from the base to the datum line? Am I misunderstanding shoulder bumping?

 

[Mram10us]

Are they deprimed?

 

[Tac-O]

Are they deprimed?

Yes. I used a depriming die before doing measurements and sizing

 

[MNbogboy]

In order to "bump" the shoulder in a FL die the shoulder of the case has to reach the corresponding shoulder in the die. That means you will be sizing all of the neck just as in regular FL sizing. The case normally always gets longer as you "squeeze" it in a die. Only once the shoulder is reached does it the base to shoulder measurement start dropping but overall length continues to increase.
Keep turning the die down a small amount at a time to eventually start "bumping" the shoulder. Take measurements as you go until you achieve .002 (or whatever number you are shooting for). Using a different piece of fired brass for each dimension check may get you to goal sooner because once you start bumping springback changes with each successive try.
Mark the shoulder of your trial pieces with a "sharpie" you will see it start rubbing off as it first meets the die shoulder.
Note: fresh annealer brass bumps easier and farther so it is best to check often with your case comparator. (I measure every piece of brass and adjust accordingly).

 

[19 Badger]

Make sure the inside of the neck is lubed as well. If it is not, the expander ball will have a lot of resistance when pulling it back through and slightly making your measurement a little longer. Sounds like your die needs to be screwed in slightly more. Usually when I am getting close to my die setting to bump the shoulder it grows a little. Use good case lube (Imperial or Unique Sizing Wax). Annealing never hurts...

 

[Tac-O]

Fantastic. Thanks for the tips!! I think my die may not be screwed far enough in. I screwed it in even further than the manufacturer's directions for a FL size, and then it started to bump the shoulder back a bit. Strange that the directions for setting the die for doing a full length resisizing would have it not bumping the shoulders back at all.

 

[Deputy819]

Strange that the directions for setting the die for doing a full length resisizing would have it not bumping the shoulders back at all.

Check this thread out. I think you'll like it.
https://www.longrangehunting.com/threads/re-size-question.214542/
https://www.longrangehunting.com/threads/re-size-question.214542/

 

[L.Sherm]

Your squeezing the case body smaller is why your cases get longer.
Instructions in most dies suck on how to set them up.

 

[Tac-O]

Check this thread out. I think you'll like it.
https://www.longrangehunting.com/threads/re-size-question.214542/

Thanks for the link!

One piece of info I left out is that they are once fired brass, with a 150gr bullet and a low-mid range powder charge. So, I probably didn't even completely fire form the brass yet! I'll have to pull out some older cases this evening and check those.

 

[LaHunter]

You may want to check out the Redding Competition Shell Holders. These allow you to set your die for minimal sizing / shoulder bumping.

 

[Rich Coyle]

I think you need to forget that gauge. You size your case a little and check its fit in the chamber. If you do it correctly you will notice it gets a little bit harder to close the bolt. get another case. Once you get this you turn the die down no more than 1/20th of a turn down. This give you about .003". Get another case. You continue to size a different case and turn the die down until the bolt closes the same as if there was no case in the chamber. Use another case. If you like a tighter headspace turn the die back out about 1/40th of a turn. This will back it out about .0015".

Annealing is a good idea prior to doing the above.

With all that said, I measure every case I size before I size the next case. What a hypocrite! Right?

 

[Wolf76]

And keep in mind that shoulders often take 2-3 firings before they grow enough to need bumping.
I look for the one that measures the most and start bumping from there.

 

[Tac-O]

So I did some extra measurements yesterday eveninga here is what I found:

4x fired unsized federal and Winchester cases were 2.040 or 2.041 to the shoulder. Chambering these cases still didn't seem to give hardly any more resistance closing the bolt. I put a single piece of scotch tape (0.002 thick) on the base of one of these cases, colored the shoulders with a sharpie, and chambered it, which gave a stiff closing and opening of the bolt and showed rub marks on the shoulder. I then used the method of finding headspace that was in the link in this thread, where you start a spent primer by hand into a fired unsized case and then chamber it, allowing the bolt to push the primer in when the case shoulder hits the end of the chamber. So, measuring this case to the shoulder with the primer pushed in by the bolt gave me 2.043.

My 1x fired win cases that I mentioned in my original post measure 2.038 to shoulder. Given that I've only been shooting 150gr jacketed bullets with 57gr h4350, I guess I'm not surprised that even my 4x fired cases still aren't at 2.043. I also found some information that states shooting reduced loads can cause a decrease in headspace length of the fired case due to the firing pin slamming the case into the chamber shoulder and there not being enough pressure to stretch the brass back to the bolt.

I think I've got it figured out!
Except, now I feel like I'm not sure how to correctly set my FL sizing die :/

 

[bigedp51]

In one of the previous postings, they told you to get a set of Redding competition shell holders to control the amount of shoulder bump. These shell holders do not push the case as far into the die as a standard shell holder, meaning less shoulder bump. And you do not need to touch the die to adjust the amount of shoulder setback, you just change shell holders.

You can do the same thing by placing different thickness feeler gauges between the die and shell holder. Start with a .010 feeler gauge and full length resize a case and see if it will chamber without resistance. Keep going to a thinner feeler gauge until the bolt closes with no resistance and you have .001 to .002 head clearance.

And remember resizing the case and reducing its diameter makes the shoulder move forward until the die is adjusted down far enough to push the shoulder back down.