Hi Pondweed........
I am far from a competent driller of small diameter holes in brass....but am old enough to know a few tricks
Look up a table for surface cutting speed for brass
![Inocent %)](https://www.modelboatmayhem.co.uk/forum/Smileys/Tug/rolleyes1.gif)
...you will probably find a calculation for conversion to RPM per diameter
You may well find the recommended RPM for a 0.5mm diameter HSS twist drill is 20,000 RPM
You must use a pedestal drill [or a small die grinder with collets......but this
MUST be aligned in a vertical press with some form of accurate feed]
Most hobby pedestal drill as fitted chucks go down to say 1.0 mm....so a precision keyless chuck may be required
The work must be adequately supported....with accurately placed centre pop marking in the piece being drilled.........
0.3mm diameter is a very small hole......the smallest holes I have drilled in brass is 0.68mm diameter or 0.027".......& I find these difficult & testing....these are conventional two flute 115 degree included angle drills
I do have experience with single fluted "rifling" drills for deep hole drillings 8,000 mm deep .....but these diameters are 20 mm +.....I have ZERO of knowledge of single fluted fractional mm HSS drill bits......
Now in theory.......brass does not need a cutting compound, however
ROCOL general purpose cutting paste will assist
.....good luck.......Derek