Kristian, be patient with your new string on your old K Mag. I have two, both 50#, and they are the most brace-height sensitive bows I own, which makes sense given that they are only 48 " tip to tip when strung. I have and handful of 48" B-55 strings that have stretched to the point that they have to be twisted like a dishrag to get the brace height correct and 47" strings that have almost no twists left in them. With the brace height below 8", the K Mags seem sluggish and prone to wrist slap on release , over 9" and they are really twangy despite string silencers.
One of your Alberta neighbors, DDave, shoots a 1961 K Mag with a BCY-X string made by another Canadian TG member and swears that's the best and quietest string for that bow.