6.5 PRC headspace and brass stretch

[Nimbus73]

This question is pertaining to headspace for my 6.5PRC, but but can apply to any shouldered cartridge. I'm getting brass ready to size. Being that I have not reloaded many rounds for my PRC, I don't have very much multiple times fired brass. How do I know if my brass has stretched its maximum to my chamber?

For example (average of 7 rounds for each example listed to datum line): 3x fired Norma=1.6460", 2x fired Norma=1.6448", 1x fired Norma=1.6439", 1x fired Hornady=1.6443", Norma Factory Golden Target Match unfired= 1.6416", Hornady Factory ELDx unfired=1.6424"

On all of my previous loads I based my shoulder bump from a 10 round sampling of the Norma Factory ammo after the first firing to be set at 1.6420" which was about a 0.002" setback. Now that I have some with 3 firings, I've noticed larger distances from the datum line to case head. I want as little bumps as feasible preferably 2-3 thou. I'm wondering now if maybe I have been bumping more than I need to. Is setting my shoulders at 1.6430" or 1.6440" cutting my head space too tight, or should I just be content with 1.6420"?

 

[FeMan]

Sometimes new brass that wasn't pushed hard doesn't require any shoulder bump after the initial firing. It usually takes brass three to four firings to completely stretch itself out. I check each batch and adjust my die as needed until the batch of brass reaches equilibrium. To ensure I am sizing only the minimum amount required, I strip my bolt and chamber each piece of sized brass in the chamber, inching the sizer down until I get a clean close. I size and check a decent size sampling (6 to 8 or so) to be sure the bolt will close clean on all of them and often find a few that were a little longer and necessitate a little more bump.

 

[243winxb]

How do I know if my brass has stretched its maximum to my chamber?

Forget the SAAMI drawing. Means very little.
The comparator is to compare sized brass to fired. Nothing else.

Old school method.....
Start with a feeler gauge of .010" between shell holder & fl die. Adjust die down, as needed. Look for a Crush fit when closing a bolt action.

On M16 types, when the bolt will not turn and lock. Adjust die down till empty brass allows the bolt to lock.
Its possible to let the chamber size the brass. This is done by putting the 223 brass (dont know about 6.5)in the chamber & allowing the bolt to slam into the brass a few times. Only works if head to datum is .002" to long or less.

 

[Nimbus73]

What I did was to put 5 of my 3x fired brass into the chamber and close it to feel for resistance. I did the same with some of the 2x, 1x and factory. There was a noticeable difference in resistance between the 3x and any of the rest. Not a really hard to open and close the bolt, but definitely a lot stiffer. So I used my 1.646" number and started resizing, bumping back until I got it down to 1.644"-1.643". The bolt action felt good. I don't have a dissembly tool to take my bolt apart to remove the extractor and feel for resistance like some of the you tube videos I've seen. This shoulder bump is just slightly less than the average of previous loads. I'll see how that works next time I shoot. I just thought it odd to see even more stretch after a 3rd firing than 2x or 1x, so I was curious if it was normal for the brass to do that. With more firings, I will get more data telling me what I need for a .002" bump. With my AR in 6.8spc, I try for more a a .003"-.004" bump.