The rotwiel slugs are great for accuracy and penetration, they (BG) will find little that will slow one down, I have tested on cast iron wash basin with brenneke 3" 600grain and it went through one side and put 3" crack on other, better than FED, REM, OR WIN could do. Due to lead alloy slug instead of pure lead. (harder)
As to mag spring it is true some old auto pistols worked 40 years after storing with full mag (1911) but mag was made with extra room in base, look at current 8 rounder a lot less room. For good read about this go to gunspring site "WOLF SPRINGS"