hope i can explain what is happening.

I started using a Frankford wet tumbler for cleaning my brass. I love it gets brass really clean saves time on primer pockets. So I size my shells full length before I put my shells in the tumbler ( I use dawn dish and lem bright with hot water)
After I I tumble for 3 hours I take them out rinse and put in oven at 225 for about 45 min to an hour with door cracked to dry them let cool. I just did about 200 rounds of 243. I measured shells and the ones that was over spec I went to trim with a lee hand held trimmer to trim to size the trimmer will not fit in the neck. I ran some shells back through my press and it worked great. is it possible that the shells are shrinking when dried in the oven.

Any help would be great
Huntlakewood