I have one. I prefer the Hornady comparitors that you fit onto a caliper--faster to use. For both setting up the sizing die and for measuring bullet ogive lengths.
The dummy case that RCBS supplies for measuring the lands is extremely hard to get a repeatable measurement with. I don't trust it at all and don't use it. I seat a bullet long in a case, then stuff it in the chamber with my thumb. Seat it a wee bit shorter each time. When it drops from the chamber without having to use a fingernail, you now know where the lands are. You can measure the cartridge (COAL or ogive) if you want to track wear on the barrel in the future. I write the bullet on that case and save it for the next time that I need to set the die up for that type of bullet. Then the 1st production round goes in, I measure it, and then seat it 0.020" deeper (or whatever number I want for bullet jump). Way quicker and easier than messing around with dowels and slit-necked dummy cases, etc, plus your die gets set up in the process.
I believe that Hornady offerings used to be Stoney Point if I am not mistaken. 30Caliber's description of using thumb to push in and then see if it drops from chamber is the method many of us used long ago when gauges/tools were not available and as he pointed out, works just fine. Be aware that on rifle such as the M14 you will need the angled tube for as opposed to bolt gun, no way to utilize dummy round into chamber and use tool. Using caliper a real number can be determined and user can develop history of wear/tear in throat area. Unfortunately the M14(or similar rifles) limit the user to loading his rounds to max. bullet seating(2.800") in order to function through the magazine regardless of throat erosion. Single loading permits longer seating of course.
Are you talking about the headspace precision mic or the overall length gauge for your free travel in your chamber?
No I know my H.S. I'm trying too set the bullet seating depth just off the lands or what works best for the different bullets i'm using on specific chambers. If info keeps coming in I can sift through it and get a good idea of what is out there. Thank's all for the input. Packing
I like the Precison Mic for comparing headspace...easy to get consitant mesurements when setting up sizing die. Currently I really like the Redding Dial indicator for me its the best option for headspace comparing....but my Precision mic is a close second.
Keep in mind both of these are comparators....not absolute measurements. I have a forester 1.630 go gauge and a 1.634 no go that comes in handy when I need to calculate exact measurements.