When professionals roll without cores, we should not consider using them. OK if you must, then please consider a proper biodegradable material.
Fireworks gets a bad press without us filling the land with lead shot.
i roll coreless by that i mean i use either cut stars as cores that are very small or granulate some star comp then use that or dragons eggs, all make nice cores, all charcoal streamer comps should be difficult to roll first time and it is not easy to get round uniformed stars back, the trouble with using light weight cores is that the first applications of water are often too much and binds the cores or over wets the drum if using seeds or small cut stars, something you have to eye well,
coloured cut stars look really nice with streamer comps over the top it gives a sort of cavity star look for low effort.
100 small cores will be enough to carry 100g comp to 8-10mm and be enough for a 3" shell or mine, with tt etc roll 3mm at a time [20-30g on 100 cores] they dry fast if you dont over wet them, 3 days rolled up to 2 weeks cut
star rolling is more than i care to try to explain i believe you get a feel for it that doesnt translate well person to person but there are standards.
i have had success with rolling veline colours and water but i dont like the smell of chlorine so i cut them with acetone.