op amp problem

Whilst working on a power supply project, I decided that for the current limiting circuit I didn't want to lose 0.7V across a resistor as in the usual design; 0.7V at 30A dissipates 21W in the current sensing resistor, too lossy for my liking. I therefore decided to amplify the small voltage drop across the existing wiring, (I get 50mV across one wire at 12A load) and feed this output into my latching trip circuit which requires about 1.5V. Varying the feedback resistor then sets my current limit. Whilst experimenting with the amplifier, I first tried a 741 in the non inverting configuration with feedback and input resistors on 150k and 10k to give a gain of 16. With low level inputs to the + input, in the millivolts range, the 741 output shoots up to more or less the supply rail voltage, yet with inputs above half a volt or so it works as expected. I got round the problem by using an LM324, which works as expected, but would like to know why the 741, and other devices, (NJM4558L) behave in the way described.

I was thinking it was a power supply problem since im just using a single ended supply, and the 741 output cant quite reach the supply rails. I have found that the power supply is losing regulation at high load currents, the unregulated DC is dropping down to 19V at a load of 12A.  The transformer is unidentified but weighs around 4kg, comparison with similar transformers on the market, I reckon its good fro around 600W or so, plenty big enough for my needs.  Adding a few extra turns to the transformer cured the loss of regulation problem, but this increases the dissipation. Im now considering running the regulator circuit off a separate winding with a slightly higher voltage, or doing away with the 741 and making up a long tailed pair, perhaps this will make an improvement. The transformer im using is a large toroidal type which I have rewound specifically for this purpose, I found it easy to rewind since it only requires about 2 turns per volt.