I can't say you've been searching hard, but it might be for the best since the sniper rifle is still a 'v_/w_model', which renders this tutorial moot for the bigger part.

Essentially you need to decompile both models (essentially following the decompiling portion of that tutorial) and manually edit the SMD reference file, swapping out the original mesh with the new one, re-rigging it; also praying to whatever you worship might help, because decompiling 'v_/w_models' can make the animations go completely out of whack.