243 brass resizing issue??

[Lefty Trigger]

Using the Hornady Comparator to measure the fired brass from my Winchester 70 Coyote light I get a measurement of 1.624. Using my RCBS FL sizing die I'm set up to push the brass shoulder back only .002 for a reading of 1.622. The weird thing is though,... about 1 or 2 pieces of brass out of 50 will size way down to 1.620. Where is that extra .002 push coming from??

 

[BoydAllen]

Brass has spring back that varies with how it is annealed, in this case, at the factory. The two cases that have their shoulders pushed back .002 more have softer shoulders. As cases work harden from repeated firing and FL sizing, the die setting will have to be changed to produce the same amount of shoulder bump, which is why it is a good idea to use a set of cases in rotation so that they will all have about the same number of firings at any given time.

 

[Lefty Trigger]

Brass has spring back that varies with how it is annealed, in this case, at the factory. The two cases that have their shoulders pushed back .002 more have softer shoulders. As cases work harden from repeated firing and FL sizing, the die setting will have to be changed to produce the same amount of shoulder bump, which is why it is a good idea to use a set of cases in rotation so that they will all have about the same number of firings at any given time.

I only have two brands of brass for this rifle, Remington and Winchester. All of the cases that have the extra push back are Remington brass,...Weird?

 

[Homerange]

I only have two brands of brass for this rifle, Remington and Winchester. All of the cases that have the extra push back are Remington brass,...Weird?

I thought is was a general consensus that Rem brass is generally softer than Win. You're not shooting mixed brass and loading them all as one, are you ?

 

[ireload2]

The extra .002 thousandths is from variation in your sizing technique.
1. More lube
2. Slower sizing strokes
3. More dwell at the top of the stroke.
4. Double stroking or double sizing. Repeated sizing or just double clutching or jogging the ram at the top of the stroke.

If you jog the ram up and down 3 times at the top of the stroke with some dwell all of your brass will probably come out 1.622.

If you form or size 100 cases and check everyone as you go you will start to recognize small variations in technique that will cause .001 to .003 variations in sizing.
Most handloaders in a hurry will never discover this variation.

BTW
I can resize machinegun fired .30-06 brass in my Rockchucker and the press frame will stretch .002 under load. Resize the same case again and the brass moves. The frame is no longer stretched.

 

[Lefty Trigger]

I thought is was a general consensus that Rem brass is generally softer than Win. You're not shooting mixed brass and loading them all as one, are you ?

No, all matched and kept together.

 

[BoydAllen]

The extra .002 thousandths is from variation in your sizing technique.
1. More lube
2. Slower sizing strokes
3. More dwell at the top of the stroke.
4. Double stroking or double sizing. Repeated sizing or just double clutching or jogging the ram at the top of the stroke.

If you jog the ram up and down 3 times at the top of the stroke with some dwell all of your brass will probably come out 1.622.

If you form or size 100 cases and check everyone as you go you will start to recognize small variations in technique that will cause .001 to .003 variations in sizing.
Most handloaders in a hurry will never discover this variation.

BTW
I can resize machinegun fired .30-06 brass in my Rockchucker and the press frame will stretch .002 under load. Resize the same case again and the brass moves. The frame is no longer stretched.

I have seen factory brass, sized the same way, vary in the amount of shoulder bump and when it was properly, not over, annealed by the shooter that variation went away, or became very small.

Another example of the effect of differences in hardness causing large differences in shoulder bump at a given setting showed up when I had a 6PPC die set for a set of brass that had been shot perhaps 20 times testing various loads and forgot to back it off and reset it when I switched to a new set that probably had only three firings on it. Instead of the .001 bump that the setting had produced on the work hardened brass, the shoulders of the first few cases that I sized before remembering to check bump were pushed back about .0035.

Neither of us has any information about how the OP sized the cases that he mentioned, with regard to number of strokes or lubrication. The results that I mentioned all occurred using uniform procedures.

 

[ireload2]

Few people have the capability to measure the hardness of their brass so it is difficult to measure the hardness of the brass and correlate it to the length reading from the bump gage. Hardness will always be a potential variable added to the other variables. While you may claim everything is uniform it really can't be just because of the variability in application of case lube, differences in speed of the sizing stroke and dwell time at the top of the stroke. No one does that exactly the same every time, at least I don't according to my calipers.

There is a limit to how much your die setting will push back the shoulder based on the unloaded press. Once that dimension is reached you cannot push the brass back any further. If your sizing effort is leaving your press with some load on it you will always have the potential for length variations due to material hardness and all the other variables.
If you keep sizing a case and applying lube eventually you will reach the limit your press can size at a particular die setting.
I might be proved wrong if you can measure your cases to plus or minus 50 millionths (one half of a ten thousandth). But just using calipers at plus or minus .001 will not tell you much.

I have seen factory brass, sized the same way, vary in the amount of shoulder bump and when it was properly, not over, annealed by the shooter that variation went away, or became very small.

Another example of the effect of differences in hardness causing large differences in shoulder bump at a given setting showed up when I had a 6PPC die set for a set of brass that had been shot perhaps 20 times testing various loads and forgot to back it off and reset it when I switched to a new set that probably had only three firings on it. Instead of the .001 bump that the setting had produced on the work hardened brass, the shoulders of the first few cases that I sized before remembering to check bump were pushed back about .0035.

Neither of us has any information about how the OP sized the cases that he mentioned, with regard to number of strokes or lubrication. The results that I mentioned all occurred using uniform procedures.

 

[BoydAllen]

Look, we have sized almost new (perhaps three shots) magnum cases that showed a variation of shoulder bump that exceeded +- .001 and after annealing them, using the same die on the same press, with the same technique of press operation and lubrication seen that decrease to +-.0005. I have been sizing cases and measuring the effects for several decades, perhaps 20 years ago I noted the effects of different amounts of lube and dwell time on the dimensions of sized cases, which can be considerable. Since you were not present when we did the work that I reported on here, I would appreciate you not telling me what I could or could not measure or correcting me on my conclusions. If I have a question, I will most certainly ask.

 

[K22]

As Mr. Allen suggests I rotate cases. I have a group of cases dedicated to each individual rifle, normally 80 to 100 each. I have them divided into 20 round groups housed in MTM 20 round cartridge boxes, i.e. 4 to 5 groups for each rifle. I reload and shoot rotating these groups so all the cases for a specific rifle receive the same number of firings, sizings, trimmings, etc. in an attempt to keep them as uniform as possible.

I full length resize all my rifle cases with a .001 to .002" shoulder bump using Imperial sizing wax which provide uniform and efficient lubing. Even with all this I get some various in shoulder bump. But I have my die set so the cases will chamber with some very slight resistance since I try to avoid over sizing which can create excessive case stretch which can lead to head separation. Even though I use a head space gaging tool to measure shoulder bump, the chamber of your rifle is the ultimate gage to evaluate you're sizing.

 

[BoydAllen]

...and I might add your die. Not so much with factory chambers and dies but with "mach chambers that are usually slightly smaller than the usual factory equivalents, shooters can run into situations where a given die is too large to give the desired feel at the proper bump. As long as you combine gauging with using the rifle to feel the result you will stay out of trouble, but if you do not gauge and only work by feel, you can end up with more bump than you should have for case life. It sounds to me like you are well aware of all of this. I just brought it up for those that may be reading but not posting. Your reloading is obviously very well organized and thought out.

 

[Lefty Trigger]

I have seen factory brass, sized the same way, vary in the amount of shoulder bump and when it was properly, not over, annealed by the shooter that variation went away, or became very small.

Another example of the effect of differences in hardness causing large differences in shoulder bump at a given setting showed up when I had a 6PPC die set for a set of brass that had been shot perhaps 20 times testing various loads and forgot to back it off and reset it when I switched to a new set that probably had only three firings on it. Instead of the .001 bump that the setting had produced on the work hardened brass, the shoulders of the first few cases that I sized before remembering to check bump were pushed back about .0035.

Neither of us has any information about how the OP sized the cases that he mentioned, with regard to number of strokes or lubrication. The results that I mentioned all occurred using uniform procedures.

As far as how i'm doing it, RCBS FL die and using RCBS lube on their "roll pad" and dipping the necks in the Imperial media for neck lube and running one stroke on the press and holding at the top stroke for a second or two.

 

[Laurie]

I have been sizing cases and measuring the effects for several decades, perhaps 20 years ago I noted the effects of different amounts of lube and dwell time on the dimensions of sized cases, which can be considerable.

There was an article in Precision Shooting Magazine sometime around 1995 about experiences in loading 308 for the M1A/M14 XTC match rifle (mostly using the favoured years of LC match 7.62 with much harder brass than most commercial 308 makes). This was a fascinating tale of initial across the board woe and the learning curve that was gone through to finally achieve acceptable results. The most intractable problem encountered was huge variations in shoulder position after sizing, way more than the one or two thou' variations we're talking about here. (As I understand it, getting this right is even more important for the M14 design than most as a case with inadequate shoulder bump can result in a very unsafe firing condition seeing ignition with only partially locked lugs.)

Apart from making me grateful for the large improvements in reloading tools, especially dies, over the last 20 or so years, the author's main conclusion was as per yours Boyd of the vital importance of choice of case-lube, its application, and consistent press operation. Home annealing wasn't an option back then of course short of blow torches on cases standing in water, or dipping them into molten lead, so that avenue wasn't explored.