A recommendation for Bradders from me - I've got a few rifles he built, and they are all excellent.
For Service Rifle most people seem to have settled on a very similar spec:
Good Quality 18" or 20" barrel, free-float handguard/rail system, decent trigger, flat-top receiver with right hand cocking conversion. Low power optic (4.5x is maximum allowed in 'Service' class.)
For PR, add a bipod, higher mag scope (3-12x or 4.5-14x would be ok for both PR & CSR).