Need to make a point here. The formula gives maximum length for stabilization you can stretch it some by increasing the velocity. For instance 400 feet over the 1800 will stabilize a bullet that is a .1 of an inch over length.
But in the other direction there is a lot more give it takes quit a bit more to over stabilize. for instance a 230gr 45 caliber bullet is going to be considerably over stabilized in a 1-28 twist but about right in a 1-38 twist but it can be made to shoot well by reducing the load. with all that understood I will give you the max lengths for some calibers for 1-28 and 1-48.
For 1-28 twist
caliber length in inches[max for 1800 FPS]
.400 .85
.429 .97
.450 1.00
.500 1.3
For 1-48
.45 .63
.500 .78
Was this what you were looking for nchawkeye?