sounds like a JDJ custom job.my 2nd edition sierra manual ,page 171 has some data for a 1000 yard gun.
30" barrel/1 in 8 twist,gun weight=27.5 pounds.
140 MKHP/ X283 powder/fed215 primer
86gr 87(most accurate)& up to 90gr for hunting
140MKHP/ H870/fed215
82, 83(most accurate) up to 86 for hunting
140MKHP/H570/fed215
79, 80(most accurate) up to 83gr for hunting
Most accurate is the designation for 1000 yard loads.
there was NO chronograph available when these loads were developed!!BE AWARE OF PRESSURE SIGNS>