Originally Posted by j_22250
Loading once fired brass and necks do not need trimming, but they are not all the same length should that matter that much at all. Also for a different gun I have found my load and want to load a couple boxes but new brass has been purchased and am wondering if my gun will shoot any different since new brass has not been fireformed to my chamber. I found my load so I don't want to shoot a 100rds. jst to form and then load again.
In a hunting rifle, I have never noticed a small variation in case lenght to make any difference providing that all the cases were at least within specs.
On your other question about fireed cases vs new cases; occasionally you will find that new cases actually shoot better (smaller groups) than previously fired cases. However, fireformed cases should be more uniform and you may just want to fireform 20 cases (rather than 100) and then carefully reload them for optimum consistency. Actually, it would be a good idea to do this at least once to determine if there is any practical benefit to using fired cases in your particular application.
Let's face it, it is possible to shoot some very small groups with factory match ammo that is loose enough to fit into any chamber in a given caliber.