Here's something to consider? Someone or some machine cut the chamber, and not every chamber is cut to an exact perfect measurement each and every time! The person doing the reamer work might not have held to the measurement stated by the published (SAAMI) maximum chamber length!
I always measure the chamber before resorting to trimming to the published trim lengths by using a Sinclair Chamber Length Gage. It's a simple item that is seated into a fired case that the neck is cut way back and chambered. I have found rarely are they cut to the published trim lengths! Most notable what I have found is that they are cut longer then the published maximum trim lengths, onetime grossly too long that timing would have never become necessary! This instance was a barrel chamber cut by Shilen Rifles while using a body reamer and a different piloted neck reamer that opened up to the proper neck to size of the case. Had I not measured the case length I would have been trimming way beyond the actual chamber length and in this case a charred area would have developed between the point where the case mouth stopped (trimmed neck), and the where the chamber actually ended! I actually sent back that barrel because of that mistake made, and unfortunately my 25" barrel is now 24 1/2" inches but the chamber was cut closer to maximum but still very long!
When I mean too long, the chamber actually measured 2.1585" inches long, which is 0.0585" longer then the published length of a case, and 0.0685" longer then the trim to length. After is was cut a second time, it measured 2.1445" when it should have been cut to something like 2.11-2.1150" which is what the reamer Company had them set up for, but the person doing the cutting needs to pay attention to the depth of the cut for that measurement to be produced.
For an actual measurement to find your individual rifle(s) chamber length to trim to, I'd invest in the six bucks for the Sinclair Chamber Length Gage. It's cheap and very easy to use, otherwise you just might not be trimming your case necks to the proper length? Which could be longer or shorter the the published trim length your cutting them to?
Why over trim a case when you have no idea how long the chamber actually is. On another note, it would be worse to have the chamber cut too short which is why they tend to be cut so long.