Paul,

I may be in the minority here, but IMHO as long as you work on the tip only, balance when you're done, and don't let the rpms get out of hand, you should be OK.

RCKen is right about the APC props being designed carefully from hub to tip. If you trim the tips, you lose some of the benefit of that careful design. However, if you cut an APC 12 x 6 down to 10 inches and run it on a .40 (which would normally use a 10 x 6) it should work at least as well as a wooden, wide-bladed 10 x 6 that you purchased new. Those have squared-off tips, and other than being a bit less efficient than an APC 10 x 6, they work fine. Just don't alter the hub. If you have a spinner and the hub contacts the edges of the cutouts in the spinner cone, enlarge the cutouts. Modifying the propeller hub is a safety issue.

Duane Gall
RCPRO

p.s. Oops, looks like Rodney got in ahead of me there. What he said!