The answer to your question was in your basic data you proffered.
After the initial fireing, the cases have been stretched to your chamber dimisions, which in the case of the .30/30 can be considerably larger than that to which your dies will size to.
After the initial sizing, you will almost always have to trim OFB brass in .30/30, as most come from the factory trimed to near max length, and will "grow" significantly with the first firing and resizing.
You can limit the amount of "stretch", by only sizing your brass to where the die just "KISSES" the shoulder of the case. There are several ways of determining this, discussed in most of the manuals.
Don't just screw the sizing down to touch the shell holder, as with most dies except for the Lee's, this will cause it to grossly over size the case setting the shoulder back as much as 1/8" further back than it needs to be. This will result in large case stretching and fast case failure. I have some older RCBS and Lyman .30/30 dies (circa 1970's) that size the shoulders back considerably further than necessary or appropriate for the assorted .30/30's I've had and loaded for (2 b/a, 1 s/s, 7 or 8 l/a's !!). Yes, I have 3 sets of .30/30 dies; Lee, Lyman, and RCBS !
Even with warm loads in my lever action .30/30, I seldom have to trim until after 7-10 loadings, and get 20+ loadings from my cases. But I ALWAYS trim after the first firing and sizing.
I have about 2 life-times supply of .30/30 brass I've picked up at public firing range. However, I hate having to trim, ream, and prep new brass! So, I do whats necessary to avoid having to "prep" new cases!