GPMike,
Yes, Most serious shooters use some form of bullet depth measurements. Stony Point makes a "comparator" and of course there are many techniques such as smoking a bullet and "trial & error" methods. They all work, but my patent is very quick and easy.
I've never made a set of tools for the 38-55 but I have made one set for the 45-70. Save your money. The 45-70 is more like a handgun with a long barrel. The straight wall chamber doesn't have an abrupt change from free bore to rifling like a bottle neck rifle would, in fact it tapers like a forcing cone. I would load the 45-70 to "book" specs. They are not critical when it comes to brass length or bullet seating depth.
When you get into a 223 or a 7mm-08 you'll notice case length and bullet seating depth are paramount to fine accuracy. I've taken some pretty loose shooters and turned them into sub-MOAs by just "tuning" the loads.
What we are seeing now is a more "liberal" chamber depth spec from SAAMI. This is to accommodate the flood of foreign ammo that is not made to SAAMI specs. As a result, the US rifle mfg's are using more free bore now. Tikka and Sako have gone to a new chamber technology that eliminates the abrupt free bore-to-rifling and use a tapered throat, much like your 45-70. This increases accuracy and reduces throat erosion but robs a little muzzle velocity. Can't be all bad, they guarantee 1 MOA or less from the factory.
Yup, started with DOJ in DC, then on to California and Arizona. Excellent career and it gave me time to run a gunsmith shop as a second job. I'm retired now and love it. Got plenty of time to do things I've always wanted to do.
Most any reputable die brand is OK. I use exclusively Dillon pistol dies. My rifle dies have been replaced with RCBS Competition dies. I really like the micrometer for bullet seating. Here's an area that will get some controversy.