gunlaker wrote on Dec 24^th, 2014 at 10:41am:

Thanks man. The firebricks are great for both shielding me from the heat and adding a lot of mass which as has been said gives me very stable temp control. I bought a whack of them used off kijiji or something like that for peanuts. Handy to have when you get struck with the need to do some backwoods masonry.

Next time I do some heat treating I'll take a picture of my redneck heat treat oven. Essentially a lego kiln of firebrick with a tiger torch stuffed in the bottom. I assemble it as needed.

When asking these questions you need to identify the type of bullet you are casting - long heavy rifle, bullet,  medium rifle or pistol bullet.
Once identified you might ask only those that cast similar bullets to respond.

Often comments from one of the other types of bullet caster can be worthless.  The guy that gets great results with a six cavity 140 gr  .358 bullet may not have a clue about what is needed to cast for a 525 grain .458 bullet in a single cavity mold.

No substitute for mass when it comes to holding heat. And holding heat is the key to good fill out. I use firebricks around my furnace to maintain even temp when casting outdoors. Also have a sheet Aluminum folding wind break I can put around the furnace if we get a windy cold day. You can see it folded between the two wash tubs.

(You need to Login or Register to view media files and links)

Temp is measured with a separate thermometer. Use one for a while,  You see how much variance is possible with different ambient temps or when the pot gets low and you put in a new ingot. It makes me very skeptical of anything the rheostat dial says on electric pots. They don’t read anything, just a number on a dial that may have some standard indication of temp based on current draw. Real world about useless.

Boats

P/S big gas ring bottom of the table is for frying fish not casting.

I have tried everything tryable    I even made hollow .54 round balls casting too hot using a bottom pour Lee    I use a Lyman 20# pot.  The numbers do not mean anything, but the temp once set, does not vary enough to affect the bullet weight, 125 gr to 550 gr.  I only make one bullet at a time.  I hand dip using Lyman dipper with the spout in contact pulling it away leaving a bit of pool on the sprue. I throw the sprues back in the pot as I cut them off.    I have a Fluke thermocouple attached to the molds.  The only thing  using this method that really affects the weight is mold temp variation of more than 10 degrees.  

Good luck, Bob