This article investigates rings R whose right socle \(\Sigma(R)=\sum (\text{minimal right ideals of }R)\) is projective over R. This condition is known to be Morita invariant, by W. K. Nicholson and J. F. Watters [Proc. Am. Math. Soc. 102, 443-450 (1988; Zbl 0657.16015)]. The main result states that if \(R\subseteq S\) is an excellent ring extension then \(\Sigma\) (R) is a projective R-module if and only if \(\Sigma\) (S) is a projective S-module. Here, an extension \(R\subseteq S\) is called excellent if there exists a basis \(\{l=s_ 1,s_ 2,...,s_ n\}\) for S as free right and left R-module such that \(s_ iR=Rs_ i\) holds for all i and if, in addition, S is relatively R-projective. This includes, for example, matrix rings \(S=M_ n(R)\) and skew group rings \(S=R*G\) where G is a finite group acting on R such that the order of G is a unit in R.