Bedeviled by Bump — When Full-Length Dies Don’t Work
Here’s a word to the wise — not all full-length sizing dies are properly dimensioned to carry out the important task of “bumping” shoulders back on fired cases. With some dies the task may simply be impossible (without die or shell-holder modification). In fact, you may find that your attempt to bump the shoulder may actually INCREASE the dimension from base of case to shoulder datum!
We recently had some four-times fired 6mmBR Lapua brass. Using a Harrell’s collar that indexes off the shoulder, we measured the length from base of case to top of collar at 1.570″ (with primer removed). We noticed a little more resistance to bolt closure compared to fresh brass, so we decided to bump the shoulders back two thousandths. As a point of reference, we measured the same dimension (base of case to top of Harrell’s collar, primer out) as 1.5675″ on once-fired Lapua 6mmBR brass.
This Can’t Be Right …
To bump our shoulders we had an RCBS Gold Medal bushing full-length sizing die. Per the manufacturer’s instructions, we started with the die backed off 1/2 turn from contact with the shell-holder with the press ram at full height. We lubed and sized one case and then measured it. The shoulder had not moved. OK, no problem, we screwed the die down to contact the shell-holder (at full ram height) and tried again. This time the measured dimension was actually longer by a couple thousandths. The brass which measured (with collar) 01.570″ before sizing now measured 01.572″ — we were going in the wrong direction!
“Bumped” Shoulder Stretched .003″
Frustrated, we screwed the RCBS die in 1/8th turn past touching to allow “cam-over” which is necessary with some presses to actually push the shoulder back. We sized the case again, and this time the dimension had grown another .001″, to a total length of 1.573″! Wondering if there was something wrong with our calipers, we took the full-length sized brass (which previously had chambered just fine) to our 6BR rifle and tried to chamber it. Sure enough, the headspace had been lengthened by .003″ and the brass would not chamber at all.
Die Was Too Long Inside to Bump Shoulders Properly
What was going on? Here’s the explanation: the interior cavity of the die was too long so the shoulder surface inside the die was never actually making contact with the shoulder of the brass — and the die could not be screwed down any further. As the RCBS die, which was fairly tight in the bottom half, reduced the diameter of the brass, the case actually grew in length. While the brass was sized at the bottom it grew upwards because the “shoulder” section on the inside of the die was too high. As we “squeezed” the brass at the bottom it simply flowed upwards, increasing headspace.
With this RCBS die, in its current configuration, there was no way we could bump the shoulder back, even by .001″. The die would likely function effectively if we ground a few thousandths off the bottom, but we don’t think a die user should be obliged to make such a modification.
Lesson Learned: If your full-length die can’t bump your brass even when it is screwed down all the way (to cam-over if necessary), then you need a different die or you need to modify your die. As proof of this, we took out my trusty Redding 6mmBR full-length sizing die. This was set up (from experience), one-half turn off contact with the shell-holder. In that position, the Redding die easily bumped the shoulder of a fired case .002″ with no trouble whatsoever. We started at 1.570″ and ended up 1.568″ — right where we wanted to be. The task that couldn’t be done with the RCBS Gold Medal FL Die was accomplished easily with the Redding die. After lubing the case, we simply raised the ram to full height, and this moved the shoulder back .002″ as measured with the Harrell’s collar positioned on the shoulder.
Similar Posts:
- Tech Tip: Measuring Shoulder “Bump” with Harrell’s Bump Collar
- Measure Shoulder Bump Precisely with Harrell’s Bump Collar
- Measuring Shoulder "Bump" with Harrell’s Case Collar
- Tech Tip: Measuring Shoulder Bump with Harrell’s Collar
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Tags: Brass, Bump Die, Harrell's, Headspace, Reloading, Shoulder Bump
Interesting read. I think i have similar issues with one of my chambering. How would I go an modify my existing Die to shorten it to the desired length? I am an office guy so my tools are limited to very basic equipment. Also how would I be able to re-bevel the bottom??
Thanks
Trevor
My Redding Type S FL die get the job done. The 6BR Lapua cases, once-fired on my rifle, measured 1.565″ with my shoulder gage (Lee Wilson modified to my chamber dimensions). The Redding die bumped them back to 1.563″ with no problem.
I think another alternative would be to purchase a set (5) of Redding Competition shell holders which vary in .002″ increments and see if that would bump the shoulder enough so that die modification could be avoided. Only about $40 to find out.
Rick
I have run into this before and removed .010 from bottom of die or an easier way is to remove .010 from the shellholder with a surface grinder. There is still plenty of bevel left with .010 gone
Modifing the shell holder would be easier than the die. Buy some emery cloth lay out a strip on the table and sand off the top a little at a time. Use calipers to check your progress. Randy
I have the same problem with a 6XC. My Redding dies only bumps the shoulder when used in my Forster Co-ax press. In my RCBS RC4 press I have to use a groung down shellholder. Getting the different thickness shellholders does not work, as they start at standard and goes thicker from there.
Years ago I had to grind off the bottom of a 22-250 die to get this done. Back then we had to “soot up” the neck and shoulder to check bump and neck sizing. “Soot up” was a method where you held & rolled the brass at the top of a flame to deposit soot on the brass. Obviously all powder was closed and put in a cabinet before doing this.
A simple exercise would be to have all your chambers cut with “+1″ or “+2″ headspace so that your dies will work.You would still not have to over work your brass if the die is set up properly to slightly bump the shoulder to fit the “+” chamber.
A secondary result will be that most all of the other shooters ammo will fit your gun in an emergency situation, however your ammo may NOT fit another shooters gun as it might be too tight.
With that said, I must confess that all of my chambers are cut on “0” headspace.
Just habit I guess.
Roy
I had exactly the same experience with a Redding Body Die for .223 Remington. Fortunately,I was able to bump the shoulder back with just a small amount of cam-over.
I actually just very recently posted the same findings with a Lee 22-250AI FLS die. Eventually ground 0.10″ off the bottom to make it touch.
Grinding the shell holder makes all your other bullets out again.
Good article
I have the same problem with a 22-250. My Redding dies will not bump the shoulder back when used in my RCBS press. In my RCBS press I have used a buddies RCBS die set that work perfect! Purchased the Redding 3 die set and thats when I noticed our groups growing. When the NK die were used. Went back to FL die and still chamber problems I made a tin bushing placed it under the shellholder and was able to move the shoulder .001 or less. Then made one to use over the top of the brass and again only moved the shoulder around .001. Should I send the die back or just buy another brand?
When I hear this I often wonder if anyone with this experience has taken the time to remove the decaping rod and then check the head space. Most of the full length sizing dies rely on the decapping sizing button to pull back through on the up-stroke to size the neck and when this happens it sretches the whole upper part of the cartridge.
Redding makes different thickness shell holders as well. There was no mention of ” we then took out the decapping rod and sizing button” and got the the same results. for what it’s worth, my two cents.
Mark M
Mark,
Rest assured. The decapping rod was removed for this entire operation. Why? Well, when this Gold Medal Die was made a couple years ago, it shipped with an oversize decapping pin that would not fit in Lapua or Norma 6mmBR brass at all. RCBS representatives told me last week that current versions of the RCBS 6BR die ship with the correct 0.057″-diameter decapping pin.
The sizing button was also removed from the rod itself, pretty much as soon as the die arrived a long time ago.
The problem with cam over is that it forces the hardened pin into the softer metal of the press linkage, eventually egging the hole and ruining the press. the easiest method to fix this for the average reloader is to remove material from the top of the shell holder. Be careful to measure shell holder on both sides of the slot and the back to ensure that the top remains square.
If you are using a die with an expander ball, the issue can be resolved in some cases. If you remove the decapping assembly with the ball and see that the shoulder is being bumped as expected, the solution is to lube the inside of the case neck. I had the same perceived issue, but it was due to the ball friction re-stretching the shoulder on exit after it was bumped. Lube inside the neck solved the problem.
I have the same experience with several RCBS dies so I ended up grinding the shell holders. I avoid the problem now by buying Redding dies.