FUD, yes suppressors and fully automatic firearms are legal to own in most states. Provided they are properly registered. Other things that are legal to own with the proper paperwork include: short barrelled rifles (rifle with a barrel length under 16" and/or an overall length under 26"), short barrelled shotguns (shotgun with a barrel length under 18" or an overall length under 28"), destructive devices (handgrenades, land mines, bazooka, motars, etc), smooth bore pistols, and AOW (Any Other Weapons) category firearms like cane guns, pen guns, belt buckle guns, wallet guns, knife guns, briefcase guns, and pretty much any other item that is a firearm BUT appears to be something else.
You and seronac are both fortunate enough to live in states (Fl and Ut) where the owership of Class III and Class VI firearms should be quite legal. Some items require a $200 federal tax stamp as Mike Irwin stated, others are only $5, but the paperwork is the same including: area CLEO signature, fingerprints, and photos.