Changing the full scale deflection of an analogue volt meter
Your approach and understanding seems to be correct. Without a multiplier you don't have the option to reduce the multiplier resistor value to increase the sensitivity. With such a low value resistance it sounds like a moving iron type (although I haven't looked at these for several decades).

My old analog moving-coil multimeter was 20 k&Omega;/V and if yours had a similar mechanism the resistance should be 120 k&Omega; rather than 52 &Omega;.

If the meter has some charm and you wish to incorporate it into a project then you are faced with building a DC amplifier with a gain of two. At 6 V the meter will require a current of \$ \frac {V}{R} = \frac {6}{52} = 115 \ \text {mA} \$. This is too high for most op-amps so you'll need something a bit stronger.

52 &Omega; still seems absurdly low. Are you sure there isn't a short circuit?