Weird happenings resizing 6.5 Grendel to 6 ARC

[rcflyer]

I have some weird happenings going on forming some 6 ARC brass from 6.5 Grendel Alpha new brass. I have followed the various videos on forming 6 ARC brass from 6.5 Grendel. In every one of the videos I have not seen any intermediate process in the first step of resizing the neck and shoulder down from 6.5 to 6 mm other than lubing the case and running it into a 6mm ARC die. My first question is if there is an intermediate step that I need to do before running the new case into the die the first time?

Second question is why? I know the first step in this process necks the case down to 6mm and bumps the shoulder. If the die is a good quality FL die as my LE Wilson FL bushing die is supposed to be, why do I get a run out change on the neck of the case. I check my run out on the new Alpha cases and measure them at .0005 out of the box, but after I size them, I end up with .003-.004 of run out. I'm not trying to showoff, but I am running an Area 419 press which is supposed to be a rock solid accurate aligned press along with the Wilson die. So why is this happening?

Last question is again a why. I also have an RCBS FL SB 6 ARC die. I know that my Wilson die is set to bump back my fired case shoulder .002, and that is what it does to the shoulders that I have resized. I tried to use the RCBS SB die for the initial step, but it leaves the shoulder .008 longer than the Wilson die and it also induces about .004 run out on the neck. Experimenting, I tried a double step process where I took the cases that came out of the Wilson die and then ran them through the RCBS die, and what I ended up with was the correct shoulder dimension and get back to the .0005 neck run out. Now here is the question. With the two step process, I consistently get a .0005 run out indication on the Sinclair gauge. Occasionally though, I will have a case that has been run through the same two step forming be .002 smaller diameter than the rest of the cases. Why? It's really got me baffled.

Thanks for bearing though the long explanation. If I am doing this process incorrectly, please let me know.

 

[chromatica]

I have necked down several hundred Alexander Arms cases from 6.5 Grendel to 6 ARC. My first step is to run the cases carefully into a 6ARC collet die from Lee. You have to twist the mouth carefully inside the petals of the die. Once the case mouth slips in, you can run the ram all the way up and the petals of the die will clamp down around the neck and squeeze it down around the 6mm mandrel. Then I run the cases into my Wilson bushing die with one of my larger bushings - .265. Then I do a final pass with a .264 bushing. Necking down in small steps like this seems to preserve concentricity.

 

[SKWERLZ]

moving that shoulder back 30ish thou and sizing the neck is a lot for a single operation.
Might want to tackle the shoulder first and then the neck.

 

[SeabeeKen]

Second question is why? I know the first step in this process necks the case down to 6mm and bumps the shoulder. If the die is a good quality FL die as my LE Wilson FL bushing die is supposed to be, why do I get a run out change on the neck of the case. I check my run out on the new Alpha cases and measure them at .0005 out of the box, but after I size them, I end up with .003-.004 of run out. I'm not trying to showoff, but I am running an Area 419 press which is supposed to be a rock solid accurate aligned press along with the Wilson die. So why is this happening?

When you are necking down and moving shoulders, the displaced brass has to move somewhere. It will, like water and electricity, take the path of least resistance which is move forward away from the areas of compression. It will give you runout. This is why you need to fire form your cases afterward and likely trim.

Last question is again a why. I also have an RCBS FL SB 6 ARC die. I know that my Wilson die is set to bump back my fired case shoulder .002, and that is what it does to the shoulders that I have resized. I tried to use the RCBS SB die for the initial step, but it leaves the shoulder .008 longer than the Wilson die and it also induces about .004 run out on the neck. Experimenting, I tried a double step process where I took the cases that came out of the Wilson die and then ran them through the RCBS die, and what I ended up with was the correct shoulder dimension and get back to the .0005 neck run out. Now here is the question. With the two step process, I consistently get a .0005 run out indication on the Sinclair gauge. Occasionally though, I will have a case that has been run through the same two step forming be .002 smaller diameter than the rest of the cases. Why? It's really got me baffled.

It sounds as if your dies aren't adjusted the same. When adjusting a sizing die down for shoulder bump, adjust down in small increments. Just before the die starts to bump the shoulder, the shoulder will move forward. Keep adjusting down in .001 increments until you get the bump you want. This happens because as you get closer to the bump you are squeezing the body more and more, forcing the shoulder forward just before the die start bumping it back down. Again, you may have to trim the cases and fireform.
I hope this helps answer your question

 

[MasterYoda]

Getting 6ARC brass from Alpha is what I would do. Micro precision FL Bushing die also.

 

[rcflyer]

When you are necking down and moving shoulders, the displaced brass has to move somewhere. It will, like water and electricity, take the path of least resistance which is move forward away from the areas of compression. It will give you runout. This is why you need to fire form your cases afterward and likely trim.


It sounds as if your dies aren't adjusted the same. When adjusting a sizing die down for shoulder bump, adjust down in small increments. Just before the die starts to bump the shoulder, the shoulder will move forward. Keep adjusting down in .001 increments until you get the bump you want. This happens because as you get closer to the bump you are squeezing the body more and more, forcing the shoulder forward just before the die start bumping it back down. Again, you may have to trim the cases and fireform.
I hope this helps answer your question

Thanks for the reply. Part of my question arises from what you just described how to do. On my initial form sizing I came out with a shoulder measurement of 1.177 using the Wilson die, and 1.182 using the RCBS die. In both cases, the die body was set such that there was just a slight cam over (not sure that is the proper term, as the Area 419 doesn't really do a cam over) but there was solid contact between the base of the dies and the shell holder. The Wilson die is set to bump fired cases back .002, so that is what I using as a reference. I adjusted the RCBS die down by 1/4 turn and sized another piece of brass with the result of getting a measurement of 1.183. I again adjusted the RCBS die down another quarter turn, with no change. I then did the same procedure with another quarter turn down of the die, again with no change. I am trying to determine whether the die length on the RCBS is just simply too long to get any more shoulder bump.

 

[searcher]

When sizing "down", you can, in the process, make the neck longer. The neck basically gets '"squirted" forward - giving you a longer overall length on the case. You will see the same thing each time you size your brass. It will be longer after sizing. That is perfectly normal. Unless the length of the brass exceeds your chamber, I'd try to wait to trim to length until after a firing or two, as the brass will become more uniform. I'd anneal before your first firing as well, if you have an annealer. Sometimes, an improperly adjusted expander ball will mess up concentricity on withdrawal, right after the die made it great again.

As for your runout - I doubt there is anything wrong with either your press or your fine Wilson dies. When you change a neck size, you are displacing brass in what is basically an uneven brass flow. That lack of evenness also imparts stresses on one side of the neck more than the other. While someone mentioned running a mandrel into the neck, that will mask the problem, though will help a bit. Annealing it will more effectively address the issue of releasing the tensions- and turning the neck even more so to make them more uniform again.

 

[WyleWD]

Getting 6ARC brass from Alpha is what I would do. Micro precision FL Bushing die also.

+1^^^^. Alpha 6ARC is really good stuff. JME.WD

 

[rcflyer]

Thanks everyone for your replies. As I think back over the last few weeks since I started this process, what I saved on getting the 6.5 Grendel vs the 6 ARC brass was definitely worth it. Going forward, unless 6 ARC brass becomes not available, that is what I'm gonna do.