What I mean is that if all sub machine guns must be automatic then how could they ever be under the rifleman perk as is said in the loading tip screen?

Am I missing something?

I honestly can't remember that loading screen word for word. If it's semi auto then it would be Rifleman I guess, if it's automatic then it's Commando. Maybe that loading screen just called them rifles, and didn't refer to the Rifleman perk itself.

The loading screen never said anything about the Submachine Guns. It mentions the Hunting Rifle, and "versions" of the Combat Rifle and Assault Rifle. SMGs are only ever automatic.

This is why the Spray n Prey is so nasty. By default it has a suppressor on it so while sneaking it is affected by Commando, Bloody Mess, Lone Wanderer, Demolitions Expert, Mr Sandman and Ninja. Then if you find the Guns and Ammo magazines (+5% dmg to ballistic crit hits per magazine) and the Small Arms bobble head (+25% dmg to ballistic crit hits) you do crazy amounts of damage.

The gamma gun benefits from both the gunslinger and nuclear physicist perks.

What makes a gun fall under the Nuclear Physicist perk? Is it using a fusion core?

Its a select amount of weapons. Basically any legendary gun with the irradiated prefix or the gamma gun.

Added: also the nuka grenade.

Radiation damage.

Okay so it has to say "gamma" or have the prefix?

The nuka grenade also gets the bonus. So the nuka grenade would also get the explosive expert perk as well as the nuclear physicist perks

Anything with the symbol in the damage area for the weapon.