Which journals publish experimental results in pure maths?

I think one suitable journal is "Mathematics of Computation", an AMS journal. http://www.ams.org/publications/journals/journalsframework/mcom

Also, specific to algebra, the Journal of Algebra has a computational section: http://www.journals.elsevier.com/journal-of-algebra/

There is LMS Journal of Mathematics and Computation, which is currently in an unclear position, as the LMS Council (the governing body of LMS) wants to shut it down as unprofitable (sic!), but due to objections by a considerable number of members (IMHO Council is just dead wrong on this, and lives in the past, as far as publishing matters go) a special meeting of LMS will take place in February 2016 to discuss and (hopefully) reverse this.

For some reason this meeting cannot be found in LMS agenda.

Electronic Journal of Combinatorics does publish experimental things, provided they are sufficiently related to discrete mathematics.