I am presuming you may have an T/Contender "SSK" stamped barrel and its possibly stamped 358 JDJ..after the inventor J.D. Jones. 444marlin necked down to .358 if so ....
358 JDJ in 14" brl.
Maker of bullets is unspecified in this tested "Jones" data I received from his company 1985 for about 6 JDJ cartridges..includeing .358 JDJ below.
200 grain...
Imr 4198 41.0 grains max....2113 fps
H322.......45.5 grains max....1978
Imr4064...49.0 grains max....2002
H4895......45.5 grain max....1936
250 grain
748.........47.0 grains max......1861 fps
Imr4064...48.0 grains max......1956
H322....... 44.0 grains max......1920
H4895......46.0 grains max.......1939
.....if its' an SSK brl. it should read the caliber on the brl. if it was at one time purchased brand new from the company....or be appropriately stamped on the brl. on the flat surface where the hinge pin goes through it if a rechambered/ converted brl from Jones......as was mine ... a .44 mag barrel rechambered to .430 JDJ.