John 

Are you using a dial thermometer?  I've been using a digital pyrometer which seems to be very accurate but I use a propane burner and keeping the temperature within say +/- 20 F is not easy.   I guess I need to go electric

Dave

I use a Lee 20# dipper-pot with the thermostat as it came from the factory. I weigh (almost) all bullets I cast. For the last 24,628 bullets cast, the standard deviation has averaged .152 grains. Thus, virtually all bullets weigh +/-.5 grain. With a properly warmed up mold left on the rim of the pot, and after pot and mold warm up for at least 45 minutes, bullets almost always vary +/-.3 grain or less.
I have never been able to detect accuracy differences as a function of bullet weight, excluding outliers. Bullets varying from 199.5 to 200.5 grains shoot as accurately as bullets weighing 200.0 grains. Outliers are bullets weighing, per the example above, 194 or 203 grains. Many shooters agree with my experience, and I have never seen a reliable report ahowing that .5 grain variation in bullet weight yielded less accuracy than .0 grain variation.
The use of a dimmer switch to vary power eliminates the cycling of the thermostat, theoretically reduces temperature variation in the pot-but only if there is no variation in casting procedure during the session-and possibly reduces the variation in bullet weight. 
I doubt that the dimmer yields bullets with less weight variation-data is needed-and my experience is that even if weight variation can be reduced below that of well-cast thermostat pot bullets, no demonstrable accuracy improvement will be seen-again, data is needed.
The dimmer is a solution in search of a problem, as are the dial lead pot thermometer, the electronic dissimilar metal thermometers and the laser bathtub.
The above is only my experience and opinion, and I could be wrong. I'm ready to admit my error after the data arrives.
joe b.

I use a dial thermometer in my large cast iron pot, fueled by 3 gas jets.  Watch it for a while you realise how much alloy temperature variation there can be. 

It can vary due to gas setting but my experience is it's the least of potential variations.  Pot gets empty the alloy gets hotter.  No new news here ever fry fish the same thing happens you have to add fresh fish as you take out or the oil will start to smoke, or turn the heat down. Working outside in the winter have seen wind around the bottom of my furnace cause real changes in the alloy temperature.  So much I build a wind sheld out of fire bricks around the furnace. Cranking on and off the gas jets while keeping my eye on the thermometer produces better bullets.

Add the potential variation in mold temperature due to casting rate it's a important issue one of the most important.  I have been trying one of the "gun" style temperature meters but have not found it sensitive or accurate enough to be useful. Gives you a precise  read out but dependent on were it's aimed. Plus you have to stop and shoot what you want to read with no reference on were the temperature was last time you checked  or the trend. 

Dial Thermometer the needle starts to move I make adjustments.  I think casting just like frying fish or shooting rifles, no substitute for mass to minimize variations.  Cast iron furnace large pot full of alloy firebricks around the pot to contain heat and the ability to adjust the flame. I would think electric pot large capacity is also a good solution

Now the bench rest shooters will like this part, I don't weigh them. Used to but found little variation and was a real pain to do.  Give my bullets very close visual inspection and reject anything that does not look right. While casting, as they go on a tray after cooled and as they are put into  plastic individual compartment bullet boxes.  3 visual checks. If it looks good it is good is my opinion

Boats

What wire size is recommended for the Dimmer switch?

Ron

John
I have found that getting good consistent bullets is more about learning a molds personality than anything else. Some will want higher temps some want you to work fast others slow. Once I have figured out what they want I can then keep a .32 bullet within .3 of a grain after casting 10 to 12 bullets. It is more about that and rhythm than anything else. I cast with a Rapine electric pot. 

40 Rod

Just got to thinking about this casting/temp thing.  Wouldnt it be cheaper and just effective to tap into the 110 line in your pot with a jumper wire and an alligator clip?  Clip it to your arm or ear or something, and when you get shocked it will prompt you to cast a bullet, REAL FAST.     Might set a casting record doing it that way.  You could cast a years supply of bullets in one day maybe.  Maybe.  

           Joe.  

Westerner ,
Thanksgiving dinner must be a hoot.
Kurt