Shoulder bump consistency
- Thread starter jlorenzo
- Start date
Measuring every case after sizing is very revealing.
I have found that the press used makes a difference. With the Forster CoAx I have used for 20+ years, I would usually get cases to within .001" of shoulder bump, with an occasional case .002" long. When I got my Prazipress I cut that in half.
Consistency of lube application is a big factor, and sometimes there are certain case/die combinations that are more fussy.
I account for all this by setting my die to see to the long side, and then I will size again if needed. Dwell times does matter, and for whatever reason if a case sizes long the first time, it seems to size better the second time if I wait a few seconds before the second sizing stroke vs double pumping.
When all is said and done my match cases wind up to within .0005" on the shoulder, assuming the Mitituyo calipers are really that accurate. Whatever the actual variance is, this method produces the most precise cases for me.
I have found that the press used makes a difference. With the Forster CoAx I have used for 20+ years, I would usually get cases to within .001" of shoulder bump, with an occasional case .002" long. When I got my Prazipress I cut that in half.
Consistency of lube application is a big factor, and sometimes there are certain case/die combinations that are more fussy.
I account for all this by setting my die to see to the long side, and then I will size again if needed. Dwell times does matter, and for whatever reason if a case sizes long the first time, it seems to size better the second time if I wait a few seconds before the second sizing stroke vs double pumping.
When all is said and done my match cases wind up to within .0005" on the shoulder, assuming the Mitituyo calipers are really that accurate. Whatever the actual variance is, this method produces the most precise cases for me.
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spitfire_er
Silver $$ Contributor
I checked my batch of 76 today. I had decent consistency but I did have a few outliers. Honestly the first time I've measured them all after sizing. These groups were separated into 0.001" increments.
All cases were flame annealed on my diy annealer, imperial sizing wax, set up for a 2 thou bump from a chamber measurement, and sized with a wilson FL bushing die. The two large ones fit my chamber but I can feel they are snug. Large middle batch chamber freely and of course the smallest batch on left chamber freely. Then trimmed to length and chamfered. Using an old Redding T-25 press. Next time may try on my rock chucker.
I haven't kept the best track on firings and I'm pretty certain some cases may have 3-4 more firings than others. All were from the same box. Remainder are loaded.
All cases were flame annealed on my diy annealer, imperial sizing wax, set up for a 2 thou bump from a chamber measurement, and sized with a wilson FL bushing die. The two large ones fit my chamber but I can feel they are snug. Large middle batch chamber freely and of course the smallest batch on left chamber freely. Then trimmed to length and chamfered. Using an old Redding T-25 press. Next time may try on my rock chucker.
I haven't kept the best track on firings and I'm pretty certain some cases may have 3-4 more firings than others. All were from the same box. Remainder are loaded.
That's the other thing, I'm just using a Hornady classic single stage press, my bench also might have the tiniest bit of flex underneath as well. Put all these things together and it probably adds up but might not matter. I have loaded some very accurate ammo through my set up. Just trying to refine things.
This brings up another question, if I run the same piece of brass through the die more than once won't it be changing the hardness/make up of the neck (assuming I'm using a standard FL die w/ expander ball)?
Doing this has always bothered me and made me feel as though each piece that I do that to will be different from the rest in some manner. Could just be me being weird though.
This brings up another question, if I run the same piece of brass through the die more than once won't it be changing the hardness/make up of the neck (assuming I'm using a standard FL die w/ expander ball)?
Doing this has always bothered me and made me feel as though each piece that I do that to will be different from the rest in some manner. Could just be me being weird though.
Here are some principles that I found that will aid in sizing consistency:
1. Operator consistency in using bump gauge and caliper. Can you repeat measurement obtained?
2. Start with virgin cases from the same lot.
3. Dedicating a group of cases to a specific rifle.
4. Rotate the use of the cases so that they receive uniform firing and sizing
5. Uniform application of case lube.
6. Uniform operation of ram during sizing.
Despite taking every imaginable step to minimize it, some variation in bump can occur. It's not unusual for me to see an occasional variation of .001" in bump. But I have yet to detect any effect on performance. They all shoot to the same point of impact IF I do my part.
I would quit stressing out about it. Just make sure you do not over size the cases. Do the minimum amount to that will assure flawless chambering and extraction.
While I've never annealed, those who do claim that it can minimize variation. I have no reason to doubt this claim since it makes sense, I just can't verify it myself since I don't anneal. So perhaps that should be added as item 7 to the above list.
1. Operator consistency in using bump gauge and caliper. Can you repeat measurement obtained?
2. Start with virgin cases from the same lot.
3. Dedicating a group of cases to a specific rifle.
4. Rotate the use of the cases so that they receive uniform firing and sizing
5. Uniform application of case lube.
6. Uniform operation of ram during sizing.
Despite taking every imaginable step to minimize it, some variation in bump can occur. It's not unusual for me to see an occasional variation of .001" in bump. But I have yet to detect any effect on performance. They all shoot to the same point of impact IF I do my part.
I would quit stressing out about it. Just make sure you do not over size the cases. Do the minimum amount to that will assure flawless chambering and extraction.
While I've never annealed, those who do claim that it can minimize variation. I have no reason to doubt this claim since it makes sense, I just can't verify it myself since I don't anneal. So perhaps that should be added as item 7 to the above list.
I don't think it changes hardness enough to matter. When I seat my cases for my BR rifles I use a hydro press. While I haven't done a test for it specifically, I haven't noticed any significant variation in seating pressure on the cases that need more than one stroke to size.
The story is told by a concentricity gauge. If you are using a typical one piece FL die with an expander ball even with lube, because of how small the die's neck ID is, the axial force applied to the case as the expander ball is pulled through the neck will cause the shoulder to yield slightly. The effect will not be even around the shoulder with the result that the neck will be cocked relative to the CL of the case body. This problem can be reduces by using an expander die and mandrel (with the ID of the case neck lubed) instead of the expander ball. On the other hand, if you use a bushing FL die and select a bushing such that the expander ball is not creating much pull on the neck there will not be a problem. When this setup is correct you can barely feel it as the expander is drawn through the case neck, and a dry lube would suffice.
I use conventional FL dies and while I do not disagree with anything you said, a couple of things I did which helps minimize the expander ball effect on case integrity.
1. I polished the expander ball to a smooth glass like finish which helps reduce drag on the expander ball.
2. I nylon brush the inside of the necks before sizing. I use a low RPM drill which speeds up the process to remove tumble media residue and any excess carbon residue that the tumbler didn't remove.
3. I use an "O" ring under the expander assembly which allows it to "float" which helps maintain alignment with case body.
I freely admit it's not a good as what you proposed but if there any guys that want to use their conventional dies, I found that the above helps significantly to reduce drag on the expander ball.
Murray Brook
Silver $$ Contributor
Don't underestimate the Lee collet die. It produces very straight case necks in good brass.
I'm still figuring out all the different processes in regards to sizing dies. Let me see if I have this anywhere near close;
1. regular FL sizing die w/ decap and expander ball
2. FL bushing die, can be used on its own without the addition of a mandrel afterwords as long as the correct bushing is used or is a follow up with a mandrel mandatory?
3. FL bushing die followed up by a mandrel expander, separate steps. It isn't immediately apparent to me why this would be better than just a bushing die assuming you can get a bushing that puts the neck diameter where you want it tension wise.
4. What else am I missing? Trying to figure out where to go from this basic hornady die, for accuracy and brass life. Just started annealing. It seems to me my necks in my current die are being worked more than I probably need. If I did the measuring right, the neck diameter seems to be moved about 7 thou which seems heavy when looking at what others are running neck tension wise. Id need to double check that number though.
Thanks for the responses.
1. regular FL sizing die w/ decap and expander ball
2. FL bushing die, can be used on its own without the addition of a mandrel afterwords as long as the correct bushing is used or is a follow up with a mandrel mandatory?
3. FL bushing die followed up by a mandrel expander, separate steps. It isn't immediately apparent to me why this would be better than just a bushing die assuming you can get a bushing that puts the neck diameter where you want it tension wise.
4. What else am I missing? Trying to figure out where to go from this basic hornady die, for accuracy and brass life. Just started annealing. It seems to me my necks in my current die are being worked more than I probably need. If I did the measuring right, the neck diameter seems to be moved about 7 thou which seems heavy when looking at what others are running neck tension wise. Id need to double check that number though.
Thanks for the responses.
This would be neck only sizing?
Murray Brook
Silver $$ Contributor
Yes .What I do is use a Redding body die to size the case body and bump the shoulder. Then I use the LCD to punch out the spent primer and size the neck. This gives me great case neck run-out #'s. Then I seat the bullet with a seater die of my choice. You end up with very straight ammo for very little $. JMW
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