Remington 30-06 brass,new!

I got 300 new 30-06 brass form an on-line store. I bought when it was in stock,thru summer and fall.As you may know it [brass] is scarce!
I ran them thru a FLS die to take the dents and dings out of the necks. I then took the ruff edge off of the necks,inside and out. I then ,at random,checked them for length. 2.494 and a little under,good to go. I loaded them with IMR-4895 at 48 grains and a col of 3.200.
40 cases,i took to the range and my new Axis. I did some scope adjustments,like 3 rounds,and it shot rather well! After a few more rounds it started fall apart,the groups. I cleaned the gun,i did not shoot it hot,at any time. It just got worse. I checked scope moutining,stock screws and what ever i could thing of,but nothing worked????? I used all the loaded new cases and went home. I FLS all of them. I e-mailed a man from on site,here and got some ideas. I checked the length of the FLS cases. Some of them had shrunk by 20 to 30 th!!!!!!! Bad chamber,nope,i checked all my new,unsized brass and they were short[about 25% of them],by that much!!!!!!!! The necks were short.
What do you do with them????????

Maybe they will shoot better after resizing again since they have been fire formed?

If not, contact Remington. Maybe they had a bad run.