Better Late than never
I've just changed the magazine axle on my HW100 .20 after having some issues with the indexining . Occasionally the mag wouldn't fully rotate which meant when closing cocking arm the pellet probe would catch the edge of the mag preventing correct loading of the pellet .
I've shot 17,000 pellets through it + whatever the first owner fired so wear on the mag axle is possible even on a HW.
1) Remove action from stock
2) I removed trigger to give better access
3) Splitt action by removing the two long bolts.
4) Remove the 2mm Allen head grub screw underneath