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Old December 29, 2011, 01:04 AM   #1
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Bumping shoulder back

Just wandering what you do, when resizing do you run sizing die all the way down on rifle brass until it touches the shell holder or do you do something else to measure exactly how much you need to bump shoulder back and stop there? Just curious. I have FL RCBS dies and have always just touched die and shell holder. Also neck size others as well.
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Old December 29, 2011, 02:51 AM   #2
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Short answer is

1. Use a cartridge headspace gauge of some type (Wilson, RCBS) to measure the difference between fired case and resized case. I believe a difference of 0.002" is considered OK. Adjust resizing die until you get this difference.

2. For bolt-action rifles, use the rifle's chamber as a gauge. Resize, try to chamber. Adjust resizing die as necessary and repeat until the bolt just closes.

My understanding is that you have to measure. "Touching the shell holder" or "Touching plus 1/8 turn" just aren't going to produce the results you want.

Without gradual adjustments, the "chamber test" can allow over-resizing. The idea is to stop when it works, instead of continuing to adjust the die for an induced excess headspace condition.
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Last edited by dmazur; December 29, 2011 at 02:58 AM.
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Old December 29, 2011, 06:36 AM   #3
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New way.

Old way.

1. Put the Shell Holder in the press and raise the ram.

2. Screw the Full Length(FL) Die into the press so it is about a "nickle's thickness" above the Shell Holder.

3. Lube a "Fired" case (walls and inside the neck) and squash it.

4. Remove the Lube and try closing the bolt on it in the chamber.

5. If the bolt closes with no resistance, screw the FL Die into the press about 1/8-1/4 turn and repeat steps 3 & 4.

6. As you feel the resistance begin, slow down how much you screw the FL Die into the press so you are at about 1/16 of a turn, or "Fine Tuning". At some point you will not be able to close the bolt and you are extremely close to having the FL Die in the proper position.

NOTE: The reason for this is because the FL Die has begun Resizing the Case-walls down to the Pressure Ring. As it does so, the Case-body lengthens slightly which in turn moves the Case-shoulder slightly forward. Then as the "Fine Tuning" continues the Case-shoulder makes contact with the FL Die and is moved slightly reward(or slightly shortens the Case-head to Case-shoulder dimension).

7. Stop when there is a slight bit of resistance when closing the bolt on the empty case. You now have a "slight crush fit" for the case in that specific chamber, or Zero Headspace.

8. At this point I screw the die into the press about 1/16 of a turn for a slight shoulder bump.
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Old December 29, 2011, 08:30 AM   #4
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I agree except with steps 5-7. If you size it and do not feel any resistence then back the die out 1/4 turn. If the case isn't sized fully you will feel the resistence when closing the bolt.
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Old December 29, 2011, 08:54 AM   #5
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If you set the die up as in step #2, the die does not contact the shoulder. The only way for the die to contact the shoulder is to screw the die into the press. Backing the die out farther than step #2,an 1/8 in off the shell holder will only result in partial neck sizing and most likely not even make contact with the case body let alone the shoulder.
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Old December 29, 2011, 01:39 PM   #6
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Do you guys think it would be a good idea to just neck sizing dies along with FL also and neck size most of the time until you have to FL size? I want to get everything I can out of accuracy but if you keep running down the FL sizer to bump your shoulder slightly wont it as well have to slightly start to size your case as well and this will not be a tight chamber fit????
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Old December 29, 2011, 03:10 PM   #7
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There is no need to set a shoulder back further than it's fired location when resizing, it's already shrunk back at least a thou anyway.

The headspace tolerance on most bottle neck cases is about 6 thou. A die moves almost 72 thou per turn (14 turns per inch) so a quarter turn moves the die about .180"; that's a massive change! A change of 1/8th turn moves the die some 9 thou, about 50% more than the full tolerance range. Meaning stick to 1/16th turns if you want to get it right without by passing the mark.

Adjusting a sizer 'right' demands a gage that reads shoulder locations in thousanths. That means either the Hornady or Sinclair cartridge head space tools on a caliper OR the RCBS Precision Case Mic (toss the dummy cartridge seating gage device) OR the Innovative Technologies dial indicator tool.

Neck sizing is vastly over-rated for accuracy and case life in factory rifles. Most will shot as well or better when the cases are FL sized and there's little or no difference in case life.
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Old December 29, 2011, 04:14 PM   #8
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Your decimal is in the wrong place. It would be 0.018".

You do need to check the cartridge in your gun's chamber during the sizing process. Pressure on the case means brass is going to move. It is as likely to move the shoulder forward as not and if the die is not adjusted far enough down to stop it the case may not fit in your gun.
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Old December 29, 2011, 10:11 PM   #9
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For my single shot and bolt action riflles, I neck size and use a body die when needed. For gas guns always FL size. I have found that my runout tolerances are better when neck sizing and works the brass less. Invest in a good set of headspace measuring tools and take the time to learn how to use them. Personally, I use three (RCBS, Hornady & Innovative Technologies) when setting up sizing dies and compare measurements.

Screwing the die into the shell holder may result in oversizing for your rifle. The procedures mentioned above work but I prefer using gauges.
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