Sorry for the delay following up on this issue (thank you for the great feedback and diagram). As described above, I experienced case stretch at datum line while FL resizing. The Question - What is causing the case stretch? Possible culprits:
(1) 2x Fired cases are not yet fully formed to 223AI chamber.
(2) Issue of fit between the chamber and the FL Resizing Die?
Resizing Die's body length or shell holder are too long compared to rifle's chamber. This is preventing the fired case from fully seating and make contact with shoulder of the FL Resizing Die that results is a small gap (excess space). As the expander button is being pulled back out of the case, it drags/stretches the case shoulder upward creating case stretch at Datum.
I was finally able to break free to tested some twice (2x) fired cases through my 223AI rifle. These cases were measured with micrometer before and after resizing and displayed case stretch at Datum from the FL Resizing. These reloaded cartridges still fit into my rifle with no issues (this favors #1 as culprit), with only the longest giving any resistance to closing the bolt. After firing I knocked out the primers and measured the 3x fired cases. The headspace/case length measurement all increased, and at same time stabilized (uniform) across the fired cases. So it looks like both #1 and #2 were in play.
I have verified the venerable wisdom that fire forming cases take 3x firings before they truly mirror the rifle's chamber.
My next step is to clean the 3x fired cases and run them through the FL Resizing Die to see if #2 is still an issue. If this case stretch still occurs after resizing then I will address it with a shorter shell case holder (Redding Competition Shell Holder set.... backordered).
(1) 2x Fired cases are not yet fully formed to 223AI chamber.
(2) Issue of fit between the chamber and the FL Resizing Die?
Resizing Die's body length or shell holder are too long compared to rifle's chamber. This is preventing the fired case from fully seating and make contact with shoulder of the FL Resizing Die that results is a small gap (excess space). As the expander button is being pulled back out of the case, it drags/stretches the case shoulder upward creating case stretch at Datum.
I was finally able to break free to tested some twice (2x) fired cases through my 223AI rifle. These cases were measured with micrometer before and after resizing and displayed case stretch at Datum from the FL Resizing. These reloaded cartridges still fit into my rifle with no issues (this favors #1 as culprit), with only the longest giving any resistance to closing the bolt. After firing I knocked out the primers and measured the 3x fired cases. The headspace/case length measurement all increased, and at same time stabilized (uniform) across the fired cases. So it looks like both #1 and #2 were in play.
I have verified the venerable wisdom that fire forming cases take 3x firings before they truly mirror the rifle's chamber.
My next step is to clean the 3x fired cases and run them through the FL Resizing Die to see if #2 is still an issue. If this case stretch still occurs after resizing then I will address it with a shorter shell case holder (Redding Competition Shell Holder set.... backordered).
