I'm assuming your 175 load touches lands having a COAL of 2.750". However, the base to ogive distance at which the bullet actually touches the lands is the critical measurement, not the COAL. Although accounting for 50 thousandths difference seems a bit much, bullet OAL can vary quite a bit from lot to lot, or even within the same lot. Also, how you made up the dummy round and measured it is important. It is very easy with only slight pressure to push the bullet 5 to 10 thousandths into the lands without realizing it. Trying to compare measurements made by two different people at different times to this degree of accuracy is not likely to be very meaningful. In addition, there is no way to know how many times each of the reamers used for the two chambers had been used and/or honed. Variation in two chambers will almost always occur, even with the same smith and tools.
I use the Hornady OAL gauge with Mitatoyu calipers (.0005" readability) and typically measure the chamber/comparator dimensions (base to ogive and OAL) with 10 bullets from the same lot, just kissing the lands. I use the average of the 10 measurements to set up my seating dies for specific base to ogive and [approximate] OAL dimensions. Many of the numbers measured for reloading are at best only "relative" to the specific individual and tools doing the measuring, rather than hard and specific. Whatever you have measured your dummy rounds to be when kissing the lands, just use those numbers to set up your load for the specific jump/touch/jam you want, even if they are slightly different from someone else's.
Inside joke.
