Dont be bummed!
The virtue of cast bullets is not just way cheaper than those with coats, its that YOU get to use the one(s) that actually fit your throat and barrel. The guys back 'in Pope's' day were getting great groups with home cast bullets in non-SAAMI bores, the standardization only made it a bit easier for us. The biggest mistake Ive seen guys do when using cast bullets is to use those too small, they see that the jacketed is, say, 429, so they size a lead bullet to that and wonder (usually) why it wont group. That hard jacket can hang onto a slim thou' of rifling and still get enough spin to stabilize. A lead bullet will likely slip it, and the gas from behind will be cutting up the base like a blow-torch into the grooves and down the sides.
Now, a soft lead bullet may 'bump up' to groove dia. real quick, and seal it off before the cutting. A WWt. or harder needs to be groove dia. (to .001 over) depending on what the throat in the chamber allows you to use. That is the ideal, even larger dia. is OK because it will swage down to bore size once it gets there., it needs to fit the critical throat dimension. If you want more of an authority, ask C.E. Harris and/or join The Cast Bullet Assoc. and/or see the Cast Bullet Forum here on GBO. I didnt invent this wheel, but I did re-invent some of it, at no little time, expense and frustration, so I know it works. Since following this methodology I have minimized the frustration curve and have got all mine to successfully shoot lead.
FWIW, the quickest and easiest start is a Lee mould (get a dbl. cav.), Lee Liquid ALOX tumble lube (or pan lube of your own) and something like Unique, though Im loving Trail Boss now.
Cast and see if an as cast bullet fits into the fully fire formed case mouth. If so, dont resize those cases, they will be too small (actually sized for jacketed 'undersize' bullets), and if you press the right size bullet into an undersize case it aint a good thing.
Decap, recap, charge and put a tumble lubed bullet in; what could be easier. Dollars to donuts it will go where its pointed. If not, somebody here will buy that rifle and they will make it work if you dont want to mess with it!
What could be better?