why are these two figures different? what if you are over the trim to length but not at the max. length. Do you trim it anyway?

KYNADOG,
The central clearing house for the fire arms industry is S.A.A.M.I.. Usually called "sammy". They set standards so a Winchester made .30-06 cartridge will fit a Remington rifle or any other brand of rifle. The SAAMI spec maximum case length for a .30-06 is 2.494". The suggested trim to length is 2.484". If a rifle chamber was 2.494" long a case that was 2.500" long would be forced into the bore, which is smaller than the diameter of the case neck. When the rifle were fired, the neck would not be allowed to expand, resulting in pressures being raised to a dangerous level. The results at best might be a damaged rifle. At worst, a seriously injured shooter. Theoretically as long as the case length doesn't exceed the max length, it is safe. SAAMI suggest .010" trimming to be safe and still have plenty of neck to hold the bullet. If a case is .010" short it maynot be necessary to trim every time the case is fired. I hope that this is of some help. Good luck.

The chamber length for the 30/06 is 2.505" and that dimension is just toleranced in general in my reference as +-.015". Nobody knows if any particular chamber is made to tolerance until they measure it.

I have always trimmed long necked cartridges to -.010" of max and short necked ones to -.005". This has worked so far.