Trim to the minimum length after resizing. It is good that 243winxb teased it out of you that you are trimming to maximum length. You don't want to be at maximum length because you don't want the case neck being pinched in the chamber throat. That is the whole reason you are trimming, to keep the case neck out of the throat.
I have not found any measurable changes or anything happening on target with cases trimmed excessively or even, randomly. It is possible work hardening might do something, but, it all depends on how many angels are dancing on the bullet when it gets launched. What you see with internet experts who don't actually shoot anything but their mouths, is that all the unsolvable theoretical issues they talk about, have a tiny affect compared to sight alignment and trigger pull. Shooting is a skill. I was squadded one day with a President's 100 shooter, his reloading techniques were barbarous. He filed the ends of cases when they felt tight in the sizing die,threw his charges, did not worry about case or bullet run out. He did none of that "bench rest" stuff. He was concerned that his ammunition chambered, extracted, and whether the bullets were good. Yet he was a National Champ. He could read the wind, and his bullets went where he pulled the trigger. The difference was between him and internet Goofy Dick experts is that his sights stayed on target throughout his trigger pull and his follow through was consistent, shot after shot.
I have been creating 270 Win cases out of 30-06, because I have 5 gallon buckets of 30-06 brass from my NRA Highpower days with a 30-06, and after sizing, the resized 30-06 are about 2.500". According to the book, max case length for a 270 Win is 2.540" . I have taken my 270/30-06 cases out to CMP Talladega and they shoot inside the ten ring all the way out to 300 yards. I have not tried them at 600 yards because I don't plan ever shooting at anything that far away with a sporter rifle. Though, in the interest of science, I may get bored and want to see what happens at that distance with my hunting rifles. I did test one 30-06 M70 with a 6X Burris on top, and my seven shot group at 600 yards was 7 3/4" in size. I would have put more rounds into the ten ring, out that box of ammunition, but shot 13 rounds just getting the scope zero'd at that distance.
Had a dead nuts 300 yard zero, so wanted to see what would happen at 600 yards.
Out of the first 13 sighting rounds, with a dead center 300 yard zero, only 7 managed to hit the target!
Once dialed in though, good group.
My 270 Win FN Deluxe is not as accurate as the M70 in 30-06
but even with 30-06 cases necked down to 270 Win, and thus, .040" short, it still shoots fine for a hunting rifle.
