Got a Fiskars X25 after reading about it on here and on Fiskars website. Tried it out on some oak, cedar and red oak. Some of it was gnarly and had knots in it. Stuff that didn't have knots in it I still had trouble with. It would get stuck numerous times, wouldn't go completely through. Is it that it's not sharp enough? My form? Is the Fiskars X27 different than the 25?