Just fwiw my favorite nn for Magnus is Max! With Mcgee in a close 2nd.
I’d also suggest…
Sullivan nn Sully
Absalom nn Sol/Sal
Cordovan nn Cord/Van/Don
Donovan nn Don/Van/Nova
Aloysius nn Ali/Al/Wish
Amasa nn Ace/Mozzy
Anatoli nn Nat/ Toli/ Oli
Archibald nn Archie
Callaway nn Cal
Cassander nn Cass / Andy
Catcher nn Catch
Mcgyver nn Mac / Guy
Mccoy nn Mac / coy
Credence nn Creed
Lorenzo nn Enzo
Halloran nn Hal
Ignatius nn Iggy / Nat / Nash
Iker nn Ike
Jazaniah nn Jazz/ Zane
Jemison nn Jem
Leveson nn Levi
McAllister nn Mack
Nicodemus nn Nick/ Cody/ Dean
Percival nn Percy
Perseus nn Percy
Roscoe nn Ross / Rocky
Rockwell nn Rocky
Taft
Tennyson nn Sonny
Thatcher nn Thatch
Tollin / Tolliver nn Tolly
Truman nn True
Wallace nn Ace / Wally
Zenebe nn Zen
Rutherford nn Rue / Ford
Some oldies with fun nicknames…
Phillip nn Flip
Richard nn Hitch
Roger dd Dodge