TECH Tip: How to Adjust FL Dies for Correct Shoulder Bump
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How Much Shoulder Bump Do You Want?
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 Set Your Dies for Correct Shoulder Bump
- Tech Tip: Shoulder Bump — How Much Is Enough?
- How to Set Up Full-Length Sizing Dies and Control Shoulder Bump
- Cheap Tricks: How to Measure Shoulder Bump Using .45 ACP Case
- Bedeviled by Bump — When Full-Length Dies Don’t Work
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Tags: Dies, Full-length Sizing, Headspace, Shoulder Bump
Not so sure about this as I use the Foster bushing bump dies that dont size the body at all, just bump the shoulder and never had a sticky problem even after ten loads for palma rifle.
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.
IMO, if you don’t ever have to size your cases near their heads, there are shooters who routinely shoot hotter groups than you do.
Some time back, a friend who does his own work, and who tends to be a bit thrifty, chambered a barrel in .243 AI. His plan was to neck size with a Lee collet die, and bump with a die that he made with the chambering reamer. I told him that since he wanted top velocity, that eventually he would have to size the back ends of his cases. It happened just the way that I predicted. To save him the cost of a FL die, in an oddball caliber (more expensive) I picked up a non carbide, RCBS .45 ACP die set for $10 at a gun show. With its internals removed, the FL die became in effect a ring die, that solved his problem. Since then, others whose reamers turned out to be just a little too small for their FL dies have successfully use the same trick. It is all about how hard the case is, and the pressure level.
Merely removing the firing pin assembly will not provide the “feel” necessary for a bolt with a plunger ejector. You have to remove everything that influences cartridge chambering.
Boyd – solid idea on solving case head sizing with odd cartridges. If I’d had that information, it would have saved me the cost of a carbide drill. Thank you.
Nice hack with the .45 die. You have just saved me the cost of a Redding body die. Thanks