Here are the results of a little experiment that I did to satisfy my own curiosity. I've seen posts asking about neck length and thickness when forming .243 Win out of 7mm/08 or .308 Win brass, .25-06 Rem out of .30-06 Spgfld or .270 Win. I've also seen questions and answers regarding "how big a step" up or down was OK. The answers that I've seen recommend no more than about a 0.030" caliber change per step. This rule of thumb has worked for me, at least where .308"-to-.277" forming is concerned. This means that there should be one or more intermediate steps taken when going from a .308 Win (0.308") to a .243 Win. I recently formed some .270 Win out of .30-06 Spgfld brass. These cases are shorter than standard .270 cases.
While neck sizing the cases after fire-forming, I started to wonder if I could stretch the cases by repeatedly neck sizing the case. In each instance, I measured the fired case, and then measured after each 'neck size'. Interestingly, it seems that the cases initially stretch, and then start to shrink (presumably due to work hardening) after a few sizing operations.
Here is a table of my results:
| Step | Case 1 | Case 2 | Case 3 | Case 4 | Case 5 | Case 6 |
| unsized | 2.504 | 2.490 | 2.499 | 2.512 | 2.508 | 2.491 |
| #1 with mica | 2.507 | 2.493 | 2.501 | 2.513 | 2.512 | 2.494 |
| #2 no mica | 2.508 | 2.495 | 2.503 | 2.515 | 2.512 | 2.495 |
| #3 no mica | 2.511 | 2.495 | 2.501 | 2.515 | 2.495 | |
| #4 no mica | 2.510 | 2.493 | ||||
| #5 no mica | 2.508 | |||||
| #6 no mica | 2.510 |
Notice that for Cases 4, 5, and 6, I stopped sizing after two consecutive identical readings. It seems that these cases can be expected to stretch 3-5 thousandths. Also, after 'multiple sizing' operations, I annealed the cases to prevent case neck splits.
I hope this write-up proves useful to you. Good shooting from the Spirit of '76 Gun Pages!!
Last updated : 27 August 1998