JB.
It's hard to say what is going on with out seeing you cast.
You say you are getting vent hairs and frosting,and still getting unfilled bases and viods.That can be a couple of things causing that.
Your sprew plate is to tight,it should swing freely by it self when the mould blocks are closed.
Another is you have oil or some lube under the sprew cutter,and the voids in the bullet ogive.
Clean the mould good with some kind of solventand boil a pot of water with the moulds. I do this with the moulds I oiled for long unused storage.The moulds I use every weak I dont oil.You can clean the moulds with alcahol or some other degreaser and that wont get it all.It will burn out after casting a few bullets that way.
I take a rag that has lube on it and i wipe just a little under the hot sprew cutter so the alloy dont build up under it and the blocks,and take a clean dry rag and wipe it off.If you use to much your problem will start all over again,a little goes a long way but I feel it is neated to keep the solder from building up under the plate.
I dont cast hot,I cast the 1 in 30 alloy at 750 to 775 deg. when I see frosting under the sprew plate the soup is getting to hot.For the paper patch bullets I cast almost pure lead (1-50)but at a higher temp is neated to fill the mould arround 800-820.
As far as the vent hairs-I get then when I hold the head presure from a full ladel to long on the plate at 775 deg.that is good it shows the mould venta are doing there job they dont hurt a thing it shows your mould is filling properly just take a rag and wipe them off.
The way I tell when my mould is at proper temp is when it takes the sprew to set dull in 5-6 seconds.
A nother thing when opening the mould dont get in a hurry,if you open it to soon you will stretch the bullet out of round,tap the hinge pin a little ,let the weight of the handle open the mould.Even the best lathe bored moulds from Steve Brooks or Paul Jones will get out of round if you open the blocks to soon.
Sorry I did'nt want to get to windy with the answer,but I hope it will help you some.
Lp.