Problem bumping shoulder

[Captbrandon]

I just attempted to bump the shoulder back on some twice fired hornady brass and I'm not getting any results. I'm using a rcbs fl die, screwed in to contact the shell holder, then backed out one complete turn. This is what I did previously with this exact brass (300wm) and easily achieved my desired results of bumping the shoulder back .015". Last night I kept adjusting the die down until I made contact with the shell holder and using my hornady headspace comparator, showed no change in headspace. Finally at just SLIGHTLY past contact the press camed over and the shoulder bumped about .025. I'm not sure what's going on. I tried extra lube in the case neck just in case I was pulling the shoulder back out with the neck expander. Any ideas on this?

 

[Blue68f100]

Your not suppose to back the die off after making contact. That is normally whats down with the seating die so you don't crimp. Screw the die back down till it contact the shell holder and normally 1/4 turn more is required. I prefer to start at contact then check and proceed from there, lowering till I get what I want.

Keep the lube away form the shoulder or you will get hydraulic dents.

Make sure the die is tight and full stroke the ram for consistency. Also different mfg of brass will have a different hardness and size differently unless you anneal.

 

[MEHavey]

First (as Blue notes), sizing is generally at near full shellholder contact -- or even a tad more (cam-over).
Second, would you mind repeating what you think the bump-back dimensions should be ?

 

[Captbrandon]

First of all, I mistyped my bump back. .015 is incorrect. I meant .0015.

Second.... I guess my brain went numb last night with backing the die out a full turn. It seems that's what I have read and seen in videos everywhere. That's what I did on the first time bumping this brass and got the exact results I wanted. Or so I thought. I just fine tuned the die SLIGHTLY past touching the shell holder and now getting good results.

I'm new to bump sizing so I'm still learning. Reloading overall my experience isn't expert either. In the past I've only done full length and neck sizing. Thanks for the information.

 

[Blue68f100]

0.0015" is good for most all guns, leave it there. As brass work hardens it will become less. Though some prefer a little more for simi-autos.

In general 0.001"-0.002" for bolt guns and 0.002"-0.003" for simi-autos .

 

[Nature Boy]

You might also try backing the expander ball out a bit. Sometimes it will pull the shoulder forward as you extract the case from the die. Back it out a few turns and I bet you get the shoulder where you want it

 

[Slamfire]

What you are experiencing is the primary reason I have cartridge case headspace gages:



The advice about turning the die down to the shell holder, plus a quarter turn, seldom correctly sizes a case to the proper dimensions. While it is well meaning, in the real world, tolerance stackup usually results in an insufficiently sized case. I do think the reputation that small base dies have of "over sizing" the case came from reloaders not setting up their dies with case gauges, and over pushing the shoulders way back in a small base die.

If the combination of die, press, and shell holder will not push the shoulder back 0.003" from the top ledge (No Go) on the case gauge, then the die is too long. I do not recommend shaving material from the top of the shell holder, I have done that, and I am concerned that the shell holder top will come off some day. I am of the opinion the best solution is to remove material from the bottom of the die. You have to be careful, just a couple of swipes on something like a diamond stone, or carborundum stone, then check to see how much the shoulder is being pushed back on resizing.You really don't want the die to be pushing the shoulder much below the lower ledge on the case gage, (which corresponds to the "Go" of a chamber headspace gauge). I have reduced the length on a number of sizing dies, particularly Lee dies for military calibers. Just take your time and use your cartridge headspace gage to see just how much you are sizing the case.