Tech Tip: Shoulder Bump — How Much Is Enough?
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.
Similar Posts:
- TECH Tip: How to Adjust FL Dies for Correct Shoulder Bump
- TECH Tip: How to Set Your Dies for Correct Shoulder Bump
- Cheap Tricks: How to Measure Shoulder Bump Using .45 ACP Case
- TECH TIP–Poor Man's Headspace Gauge
- How to Set Up Full-Length Sizing Dies and Control Shoulder Bump
Tags: Body Die, Die, Preacher, Redding, Reloading, Shoulder Bump
I guess I need clarification- I use Dillon dies for my .308 in an RL550B progressive reloader. If this die sizes the whole case this includes the neck, shoulder and body-I think. Is this still an FL die? If so how can I adjust it to possibly change the amount of “bump”. I suspect I am completely missing something here, perhaps I just need the name of a good book on this type of reloading.
EDITOR: A die that sizes Neck, Shoulder and Body is a Full-length die. There are both conventional FL dies and FL dies with bushings for the neck, such as the Redding Type “S” Die.
The way you adjust for the amount of bump is simply to screw the die down in the press (in your situation, down in the die-holder), so that it moves relative to the shell-holder. The “catch” is that it is not unusual to be unable to move the shoulder back if your press is not set to “cam-over”. Meaning, in a conventional press, the die is set to touch the shell-holder, but then you move the ram away and screw the die down a little more. With a progressive press, you may be unable to induce “cam-over” as effectively as you can with a conventional single stage press. The slop in the press makes a difference. For example, with my 6BR FL die, when using a rigid “O” press, I get sufficient shoulder bump even before the bottom of the die touches the shellholder. When I put the same die in an RCBS Turret, which has a lot of flex, I have to set the die 1/3 revolution down past “just touching.”
Shooters of AR-15s, bear in mind you need more shoulder bump than with a typical bolt-action gun. If you only bump your shoulder only .0015″, you’re guaranteed to have a feeding problem in an AR-15. For AR-15’s, you need to bump the shoulder of your cases .003″ – .005″.
By the way, if you have a Redding Competition seater for the cartridge you are shooting, you can take out the sleeve from it and use it to measure the amount of shoulder bump (head space bump) when you set up your resize die. Stick a fired case in the sleeve and measure from end to end (back of the case to end of sleeve), then put a resized case in it and measure from end to end and the difference between your measurements will give you an indication of how much shoulder bump your resize die is departing to the resized case.
— Robert Whitley
Ive loaded and fired literally tens of thousands of rounds in service rifle competition with a AR over the years. I bump the shoulder .002 and have NEVER had a problem with either a Wylde or CLE Frank White chamber.
With certain chambers you may not be able to bump the shoulder even with the die turned down to the shellholder. Ive had cases where ive needed to reduce the height of the shellholder by holding it to the side of a grinding wheel. GG
I’d like to add that we don’t see reduced case life in bolt guns even with shoulder setback of say .005″. The primer pocket in the brass is usually loose before the effect of too much shoulder setback becomes a problem. I personally use about .003″ in my bolt guns.
John Whidden
Whidden Gunworks
Just to clarify my above post, there appears to be little difference in small shoulder setbacks as they relate to case life (.001″-.007″). It is not a good idea to use large amounts of shoulder setback (say .020″) because it will indeed reduce case life and lead to case head separation.
The Redding Instant Indicator is an excellent tool for solving this. Measure a fired case which is now the size of the chamber and then set die to get the desired setback.
http://www.sinclairintl.com/reloading-equipment/measuring-tools/case-gauges-headspace-tools/redding-instant-indicator-prod33548.aspx
I use this all the time to check and recheck.
I minimal bump but have found that you have to anneal first. I have loaded ammunition that has been fired 3 or 4 times with a minimal bump to find they will not chamber two months later. Even though they would chamber at the time they are loaded. It seems as the brass work hardens and becomes springy and develops a memory.
Great info gents
It seems to me that the first firing of new brass determines the life of the case, if the chamber is minimum headspace compared to a maximum headspace chamber that means everything concerning case life concerning head separation (discounting neck splits and primer pocket enlargement). I think Whidden is right on.
At the beginning of the article was the “assuming the die fits the chamber”. There is the whole issue. Without a good match between the two, you are chasing your tail. You don’t know if the shoulder diameter is causing the feel, or the shoulder forward face. Could be the base is big and is what is causing the feel. Could be simply the brass is too long and is jamming into the chamfer at the leade. Lots to consider here.