300 blk out length after sizing, how long is too long? I trim to 1.358 I think when I make them. So how long is too long? And still bevok to load

A quick search to the AAC 300blk page should answer your question.

When I first started loading 300 BLK last year and forming cases from LC .223 brass I made the mistake of cutting my cases too long. After sizing they were in the range of 1.380" and I had lots of cranking of my hand trimmer to get to my target length at 1.360-1.363". Shortened my cut length for less work. The .223 cases grow from the cut length about .005-.008" after sizing so allow for this lengthening when cutting the necks off .223 cases.

Thank y'all.