TECH Tip: How to Set Your Dies for Correct Shoulder Bump
Some of our readers have questioned how to set up their body dies or full-length sizing dies. Specifically, AFTER sizing, they wonder how much resistance they should feel when closing their bolt.
Forum member Preacher explains:
“A little resistance is a good, when it’s time for a big hammer it’s bad…. Keep your full-length die set up to just bump the shoulder back when they get a little too tight going into the chamber, and you’ll be good to go.”
To quantify what Preacher says, for starters, we suggest setting your body die, or full-length sizing die, to have .0015″ of “bump”. NOTE: This assumes that your die is a good match to your chamber. If your sizing or body die is too big at the base you could push the shoulder back .003″ and still have “sticky case” syndrome. Also, the .0015″ spec is for bolt guns. For AR15s you need to bump the shoulder of your cases .003″ – .005″, for enhanced reliability. For those who have never worked with a body die, bump die, or Full-length sizing die, to increase bump, you loosen lock-ring and screw the die in further (move die down relative to shell-holder). A small amount (just a few degrees) of die rotation can make a difference. To reduce bump you screw the die out (move die up). Re-set lock-ring to match changes in die up/down position.
That .0015″ is a good starting point, but some shooters prefer to refine this by feel. Forum member Chuckhunter notes: “To get a better feel, remove the firing pin from your bolt. This will give you the actual feel of the case without the resistance of the firing pin spring. I always do this when setting up my FL dies by feel. I lock the die in when there is just the very slightest resistance on the bolt and I mean very slight.” Chino69 concurs: “Remove the firing pin to get the proper feel. With no brass in the chamber, the bolt handle should drop down into its recess from the full-open position. Now insert a piece of fire-formed brass with the primer removed. The bolt handle should go to the mid-closed position, requiring an assist to cam home. Do this several times to familiarize yourself with the feel. This is how you want your dies to size your brass, to achieve minimal headspace and a nearly glove-like fit in your chamber.”
We caution that, no matter how well you have developed a “feel” for bolt-closing resistance, once you’ve worked out your die setting, you should always measure the actual amount of shoulder bump to ensure that you are not pushing the shoulder too far back. This is an important safety check. You can measure this using a comparator that attaches to your caliper jaws, or alternatively, use a sized pistol case with the primer removed. See Poor Man’s Headspace Gauge.
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Tags: Body Die, FL Sizing, Full-Length, Headspace, Neck Sizing, Shoulder Bump
Those who advise to set FL dies by feel assume the correct fit between die and chamber. If this is not the case,and the person that they are “helping” does not have a way to measure relative case shoulder location(very common)there is a good chance that the shoulder will be set back too far. After repeated firings and sizings, this can lead to case failure. Given the above, I am amazed that this method is so commonly published. If a sized case requires too much bolt closure effort at the correct bump, a different die will be required to remedy the situation.
Best thing to do is get some Cerrosafe and make a cast of your rifle chamber. Then take your measurements and you have a good starting point on what’s going on. Also remember Cerrosafe does shrink a little.
I did this with the first Savage F-open and the replacement one they sent me. I was amazed the difference in chamber sizes.
IMO – the bolt drop method is a legacy approach before decent tools were readily available. It is way too easy to over size by many thou and cause early head separation. Measuring the set back is the only way to go safely.
I take my dimensions off the fired case, after cleaning, before sizing & record those numbers for each chambering.
Use the Stoney Point gauge to verify that the shoulders are being pushed back .001″ to .002″ with each sizing with the Redding Type S FL neck bushing dies.
Case trimming is seldom required & when it does, it’s only a few thousandth’s. I’ve never had to throw away a case for incipiant case head seperation.
Talking about 6ppc & 6BR chamberings, not factory.
The bolt-feel may be “legacy” but I have yet to find 20 cases that are all the same size. You can set back 0.002″, but in reference to what? One of the 20 cases you measured? Did you measure the right case, or the long one, or the short one.
The “legacy” aproach let’s me set up the FL-sizer to within 0.001″ using shims. 90% of the cases could fit with 0.002″ less, but 5-10% need a little more to set them back to a good fit. Slight resistance on the bolt when closing (without pin).
I’ve been shooting this for over 10-12 years and have never had case defects as you describe. Some cases were resized 30-40 times this way, no issues.
If this were the case, all the plain-jane reloaders out there would be having case problems non-stop with the “turn in all the way and add 1/4 rotation” setup for their FLs
The article still does not explain how to set up your die for shoulder bump like the title implies, just explains why.
EDITOR: OK, perhaps we missed the obvious point. For more bump, screw the die down (a very little bit at a time). For less bump, screw the die up. When you get to the point where bump is starting to be achieved, a very small rotation (a few degrees of rotation) can make a big difference. You’ll need to set the lock ring as you change settings.
Dasher wrote: “The bolt-feel may be “legacy” but I have yet to find 20 cases that are all the same size. You can set back 0.002″, but in reference to what? One of the 20 cases you measured? Did you measure the right case, or the long one, or the short one.?”
NOTE: We refer to shoulder bump in terms of .001, .0015, .002. But Dasher is correct that the actual amount of headspace reduction (i.e. shoulder bump) may vary slightly among cases in a batch (particularly if they were fired with different loads).
But in reality, where the cases start, is not so important as where they END UP dimensionally. That’s why we use a tool to measure off the shoulder. In a good press, with the die set up correctly, your brass, even if it starts with different base to shoulder measurements, will end up with the same base to shoulder dimension. That’s what we’re looking to hold constant! We do recommend measuring each of your cases after full-length sizing.
You can set the die up initialy to bump too much and then add shims to get the exact bump required. That way you are not guessing with “turn in a little” but adjusting with .001″ accuracy. Takes a little fiddling for the first setup removing and re-inserting the die into the press, but easy to remove the Die afterwards and then get the same setting again because of the shims.
You’re trying to get the case as close to the headspace of the chamber, so as not to size too much to stress the brass, but also to not size it enough and get jams.
I did a write up here, but it’s in dutch, but the photos show what I mean though.
http://www.vuurwapens.net/forum/index.php?action=articles;sa=view;article=55
Initially, I use the bolt feel down method with FP removed. About half way down the bolt will encounter very slight resistance. This means the shoulder has met the chamber. With very little effort, the bolt will easily close. That means the HS is correct. If not, case needs to be bumped.
After turning the die down very little and resizing until bolt closes lightly, I put it in my Redding Instant Indicator, set the dial to zero, and use that tool to check every case. Some cases will not need to be bumped.
Setting dies by feel is based on an assumption that the die is small enough that it will size the back of the case when set for the correct amount of shoulder bump. When shooting rifles with generous chamber dimensions, and using standard factory dies (that tend to size cases more than absolutely necessary) this is generally the case, but these are not the only rifles out there, and if you have ever had a die that would not size the back of a case when the shoulder was bumped correctly, you know what I am writing about. In the latter case, setting by feel, will guarantee that bump is excessive. This is why I think that it is not a good thing to give the blanket instruction to set a die by feel. Also, if a die will not size the back of a case without excessive bump, a different die is needed. This can not be solved with an adjustment. Bottom line, there are advantages to measuring, and some potential disadvantage to not measuring. If you have been getting good results for umpteen years setting dies by feel, all that this means is that all of your dies were dimensioned to allow this approach, not that everyone’s will be.
Agreed, you have to look at it case by case in those situations. I’m working with barrel and dies made off my own reamers. Taking a remmy700 and RCBS sizer may not be as good a match to blindly size the case. However, in that situation most folks size as the manufacturer tells them to, which is always excessive. This article describes that there is more in between “manufacturer setting” and “pure-bred BR”.
Complete fire forming BEFORE bumping back shoulders will insure consistent HS measurements.