Can certain weapons not get some legendary effects when rerolling?

I tried save scumming for ages to get one inch punch on revenant but never got it and when I was rerolling tier 3 with keelhauler I never got it either (though I wasn't going for it then).

I haven't tried other normal guns since I've invested heavily in the 2 aforementioned. Is it just special guns that are like this or do I need to get a magsheer or is it class of weapon?

I'm just lost at this point and can't find any info thanks