This one will be very easy, once you get to level 28 go to a fence and buy the split point pamphlet. We will be using this one as it only requires bullets to make, then just go to a campfire with at least 25 of any ammo, go to the ammo tab in the crafting menu and start crafting split points.
This can also be done with small game arrows at level 22 if you're OK with getting all the materials for them.
Solution comes from STOUTASSASSIN67 over on trueachievements.