The good news is that if your rifle is that accurate with factory ammo, it's likely to be very accurate with many combinations of quality handloads.
1. You can buy the exact same Hornady 140 grain bullets as used by Hornady in their factory loads.
2. The primers in Hornady factory loads are very likely Federal large rifle primers.
3. Disassembling a factory cartridge will give you the weight of powder used. From this, you can research loading manuals to find the right combination of type and amount of powder with that bullet weight to give you the desired muzzle velocity.
Since the ammo factories usually load powders that are not exactly the same as cannister powders (even though they have the same designation) you can only come close. Being able to duplicate factory ammo velocity and accuracy will only come with systematic experimentation.
4. Cartridge overall length can be set same as for factory ammo. Experiment with bullet seating depth for optimum accuracy.
HTH
John
