No forget manuals, as they mean nothing about YOUR chamber.
Best to buy a chamber length gauge from Sinclair, and measure your chamber end length.
Trim to desired end clearance as each case reaches it.
I choose a tighter 5thou under, and will accept up to 10thou under. I don't subscribe to trimming them all to the worst in batch.
I like them tight to end to mitigate carbon ring formation at loaded case mouths, reduce neck/case sooting, reduce ES, and reduce trimming need, which reduces H20 capacity changing.
Your trim rate is tied to the amount of FL sizing you do. This, squeezing brass thick toward thin right up the case to mouths.
Where you don't do a lot of sizing, you don't need to trim as often, if ever.
New brass will typically pull back it's necks on 1st firing, as shoulders blow outward. So unless jammed, don't trim new cases. Wait until they settle a bit and watch them with each firing until all have reached and are trimmed to desired clearance.
The little bit of variance until then is not a serious detriment, so it's ok to hold off on trimming until needed.
Just don't let cases grow to hit chamber end, because this 'end' is 45deg and can wedge case mouths to prevent neck expansion on firing (dangerous).
