I'm guessing I'll have to extrude some bars to get a ball park figure and go by that. This is really probably not very doable without a dilatometer reading of both the clay and the glazes.
Most suppliers do not have the COE's of their bodies available. So you are not alone.
Many people have the ASSUMPTION that the clay suppliers are all staffed by real "tech weenies" and they have done all sorts of sophisticatred testing on their products. That is not always the case. IOn many cases the supply companies were started by studio artists as an additional way to make some income in the field.... and the business just grows to a larger one. Many of the bodies are developed in the same way thay you would do so in your own studio by trial and error testing... and the basic tests that you can also do. No "fancy equipment". Not monitored or developed by some ceramic engineer.
Your comment quoted above shows me that you are apparently confusing firing shrinkage with the Coefficent of (reversible) Thermal Expansion. I mentioned this in another posting on this COE subject. The two are NOT the same thing and are not necessarily related.
The COE is a property of the ALREADY FIRED CERAMIC BODY. Firing shrinkave is the change in physical sze that occurs as the chemsitry and physical makeup of the raw clay body is exposed to a certain level of heat work. As the chemical water is driven off the clay crystalsm, and the stuff that can melt that is contained in the biody is acted upon by the fluxes in the clay body, the physical mass contracts. Something that was 100 mm long comes out of the kiln at 90 mm long...... for a 10% firing shrinkage.
But if you take that 90 mm long piece of FIRED clay and put it into a situation whre it is heated again...... as it is heated up again it is going to get LONGER once again...... not by very much.... but some tiny percentage. And as it is coolled off again, it is going to return to the original 90 mm long size. THAT expansioon and subsequent contraction upon heating and cooling is the COE.
Now that piece of ceramic is already "fired" on the original firing cylcle when you put it in the kiln abnd took it to the cone you want to fire to. So at peak temperature, it is now "fired". Following the example above.... it is now at the 90 mm firing shrinkage size plus the bit of tiny expansion because that fired ceramic is now also HOT fired ceramic. As the kiln then cools down on this original firing cycle.... that FIRED ceramic is also cooling off. It then shrinks back to the 90mm size. That is the impact of the COE of that particular body. If the glaze that is ON the body shrinks about the same amount as the body........ then it fits. If not... it crazes or shivers if the mismatch is off enough to exceed the physical strrength of the glaze layer or the glaze / body interface layer.
Does all that help?
Professor of Ceramics; New Hampshire Insitute of Art
Guest Professor, Wuxi Institute of Arts and Science, Yixing, China
Former President and Past President; Potters Council