m is substituted for m of sm before the word rāj ending with the affix kvip,
Thus सम्राट्, साम्राज्यम् ॥ The substitution of म for म is for the sake of preventing the anusvara change (cf 7.1.40). Why do we say 'before राज्'? See संयत् 6.4.40 Vartika). Why do we say 'of सम्'? Observe किं राट् 5.4.70. Why do we say 'ending with क्विप्'? Observe संराजिता, संराजितुम्, संराजितव्यम् ॥
The क्विप् is added by 3.2.61, the ज् is changed to ष् by 8.2.36, which is changed to ट् at the end of a word, in संम्राट् ॥ साम्राज्यम् is formed by ष्यञ् affix, as it belongs to Brahmanadi class.,