Removing material from the center of a shaft never makes it stronger...unless you are having hardenability issues with the alloy being used (i.e., not selecting a through-hardening alloy. 300M does not have that issue.....so rifle drilling is just lightening the part. It CANNOT make it stronger. That is a wives' tale spread by people who don't understand engineering mechanics (especially the torsion formula).
I could show you all the math and whatnot but use your head....when does taking material out of anything make it stronger, unless you have some weirdo exception case.
Axle shafts are pretty well figured out at this point, LOL, there is no voodoo going on!