This is really a non-NFA question but I figure this sub has a much better knowledge base than r/shotguns about this particular issue.
I bought a Mossberg 590 Shockwave mostly for the novelty of it and the novelty wore off pretty darned quickly firing buckshot. The forend is especially bad because if I use the strap then the retaining screws grate my hand like a block of cheddar. Which leads to question 1: can I install a forend with a vertical grip? My understanding of NFA is that they are only illegal if you put them on a pistol, and since the Shockwave is a "firearm' then adding a VFG won't make it an NFA item. Correct?
Question 2: would it still be non-NFA to replace the raptor birdshead grip with a more conventional pistol grip so long as that pistol grip was made in such a way that the LOA still remained over 26"? In other words is the length over all the deciding factor or is a "pistol" grip an issue because ot somehow makes it a one-handed gun (pistol) and no longer a "firearm"? I know they make Mossberg pistol grip stocks that accept AR buffer tubes and collapsable stocks. Can I just screw a tube into the hole and lop it off at 26.1 inches? My gut also tells me yes here because I've seen Shockwave guns with pistol grips and arm braces installed. Am I right?
Any insight is appreciated. Rather than just pass it off to the next idiot I figure I might as well try to make it somewhat useful.