The best description of getting consistent weights .
Get a clock with an analog face and a second hand . Visualize pouring heat to maintain mould temperature .
Find a nominal pour time , then pour every pour inside that time window . If it takes 3 even 5 seconds to fill the hot mould with full puddles on the sprue that's what it takes . If you have one or more cavities that don't fill out or cold sprue you change the pour order or pour faster . I have a 5c that has to be cast 12345,54321 or it drops 1 or 5 cold sprue . Don't even ask about the joys of little bitty bullets . Allow cooling by the clock . As long as your pot is reasonably accurate this works . I use the sprue shine visual method , but I've been casting 15 yr , probably over 25,000 from .690 RB down to a 225-37 , and I tend to be aware of color shifts even when I can't see them ........it makes sense to someone . Use the clock at first anyway .
Do each step , pour , cool , cut , open, dump , close , repeat , within the time you've allowed , don't make it feel rushed , it may take 200 or more repetitions to get a muscle memory more possibly if you don't have something you do often that is similar motions .
I have a huge 8c iron mould when it's running smooth and I'm in the place it pours 196 gr 45 cal SWC plus or minus .6 gr and 6 holes are .3 or less . I have a 3c aluminum 45-535 that pours within 1.5 gr . I have a Lee 6c 401-175 that pours 3@175.5 , 1@174 , 1@173.2 and 1@171 plus or minus 1 gr with potentially 5 gr variation across a pour lot . 1,5&6 run cold . I don't know why , but at 25 yd in a 40 consistently 4" is good enough so if it has a good basic visual look it's good enough . You don't sub MOA 23-2700 fps from 62 gr 22s , 130-140gr , 270s and 7mm with 3-4% weight slop . 35 cal isn't so picky , 380, 9mm, 38/357 , &358 Win , with 38/35 in several revolvers and a carbine held to 3% shoot as well I can . Those are 358-158 RNFP from an old Lee 2c plain base run 850 , 1050 and 1410 fps with water dropped WW , and Unique . 4"@25 yd 38 , 5" 50&100 yd 357 revolver and carbine respectively .
I'm stubborn , often hard headed , gone the long way around for a result , and listened to many here , CB long ago , and others that were actually doing these things . I had to find that first path for a rifle the hard way with 2 very ........ persnickety rifles for myself . Once I got the first one to shoot and I looked at what was going on with 38/357 and 45 Colts successes and pick apart what I did right and wrong in a 32 Rem and figured out a barrel defect in an 06' , it all came together , clicked , and made sense .
I struggled a lot and if I had tried to only learn it from a book I wouldn't be shooting cast . The Lyman 47 read like Charlie Browns teacher in the casting section .
1 . Try stuff . If it doesn't work you've learned that that didn't work that way .
2 . 0000 steel and Kroil are a good thing to have on hand .
3 . Try again with one change .
4 . Slower powders are easier on bullets , there's a good reason why Unique is recommended so often .
5 . Lead at the breach is sizing . Lead at the muzzle is lube .
6 . Tipped or broad side holes are twist related and not always but often because the bullet isn't holding the lands . Bigger works as often as harder .
7 . If it chambers freely it's not too big .
8 . Seriously plain base WW water cooled will handle 32kpsi and is completely suitable at 18-20 bhn for 9,40, and 357 .