Hodgdon does not include data for the 124gr xtp if i remember correctly but you can use the data from another bullet that they list or you can examine the data they list for the 147gr xtp and use the difference in bullet length to calculate a load range which gives the same case fill percentage.
The data given for a 125 fmj is 4.7-5.7gr at 1.09" oal. This gives a little over 90 percent case fill. The data for the 147gr xtp is 3.8-4.7gr at 1.100" oal which results in about 95% case fill. Based on these numbers a 90 percent fill cahrge for a 124gr xtp at 1.100" oal is about 5.8gr.
So just use the fmj data, starting low and going slow.