Is it possible to use a .243 micrometer bullet seater with a .243 Ackley improved case?...
no because the case will not be supported properly when you apply pressure to seat the bullet. alignment will be an issue to as well
as the shoulder angle is different by 10-12 Deg depending on reamer used. There will be an area in the body - shoulder - base of neck area that is not fully supported as the the 30 deg shoulder of the .243 wont have full contact here.
danpd hi m8 +1 on your comment
Yes as the shoulder is blown out in an Ackley fired round the case taper slightly straightens as well, forgot abouut that bit.
If its a redding competition seater, you can ream the sleeve in the die with an ackley reamer, then it would work
Being the Contrarian of the bunch, I'd suggest you ask yourself why you need micrometer seater. If you dial in .001" do you think you'll actually get just .001" of advance on the next round? Or will it be something different? I'm betting on the latter.
Before I reached an age of Enlightenment, I wanted to shoot ultra precision loads from Match die sets but I didn't have the money. I made a micrometer seater with a turned disk that slipped over the threaded seater stem of my standard RCBS dies and was held in place by a pair of jam nuts. I would set the tail end of my vernier calipers on the disk and extend the tail down until it touched the die body. I'd then turn the seater in or out with a small screwdriver while watching the progress on my (not even dial!) verniers. It was easy to do and it seemed to work. Later, when I obtained the highly sought after RCBS Competition Dies in the hardwood box, I found that the micrometer seater worked no better. Nice piece of work, but I still got normal variances in seating depth caused by the brass, bullet ogive, and press linkage. I was disappointed, but the dies still looked very scientific and I left them mounted in my press when ever anyone was coming to my reloading room.~Muir
My need for a micrometer seater is simple..... Because I wanted one.
Sticks
I have just bought a 243 'Ackley'. Having read up on this a bit, I am fairly confident that my standard 243 Redding competition seater will work with my 'Ackley' when I actually get my hands on it. The key thing to keep in mind is that an 'Ackley' is not reamed to a standard, each rifle is an individual chambering and needs to be evaluated as such.
As with many of these questions, the only real answer is to try it carefully and see what happens. It will be a month or so at least before I can post the results of my test.
Good luck. JCS