TexasMac's Web Site
By Wayne McLerran
A PID, sometimes referred to as a three-term controller, is a device
that compares a set point (SP) or set value (SV) to the actual process
value (PV) as measured by a sensor over a period of time.  When used
to control temperature, the sensor is usually some form of a
thermocouple.  In simplistic terms, the set point or set value is what
you want and the process value is what you get.  Using a feedback
system and a unique algorithm, the PID supplies power to the pot until
the process or actual value is equal to the set or desired value.  PID
stands for Proportional-Integral-Derivative.  For a somewhat simplified
discussion of PIDs, go to
com/CSI_pages/PIDforDummies.html.  For much more information than
you need to know, run an Internet search for “PID controller”.

Casting pot thermostats wait until the temperature is below the set
point, then full power is applied until the temperature is above the set
point.  It then shuts off and the cycle starts over, resulting in
temperature overshoot and undershoot.  When used with a casting pot
a PID quickly cycles the power on and off to make small adjustments
to the amount of heat being generated in order to maintain the
desired temperature.  After it was “trained” on my pot and once the
alloy temperature increased to within 20 degrees of the set value the
PID started cycling the power on and off at approximately a 1-second
rate.  It continued the 1-second cycle once the set temperature was
reached, adjusting the applied power as necessary to maintain the
temperature.  I understand the cycle rate may be different for
different pots.

So, does using a PID result in better bullets?  The answer is it may or
may not help.  If you have an inexpensive pot that does a less than
stellar job of controlling the alloy temperature, a PID will likely be a
benefit.  Some contend that the Lee pots fall into this category.  It
may also help to some degree if you’re unable to maintain a steady
casting cadence.  If you’ve developed a good casting technique and
your bullets consistently drop out of the mould to within +/- 1gr. than
using a PID will most likely not improve the weight variance.  As an
example, prior to installing the PID, I was able to consistently cast 400
gr. bullets to within +/- 2gr.  Using the PID for the 1st time, the
weight variance of 300 bullets dropped to +/- 1.5gr.  Since then the
spread has been reduced to +/- 0.5gr.  I can't say for sure
that all the weight variance reduction is due to the PID, but it sure has

I found that the PID made casting a little easier and more accurate.  
Once it was set up and “trained” I did not have to guess what
temperature the thermostat setting on the pot was set at; and
changing the temperature an exact amount is easy.  What was
especially nice was seeing the exact alloy temperature at all times and
how it was affected when the ladle is submersed and when the sprues
are returned to the pot.  By the way, when submersed in the full 22 lb
pot, a cold (room temperature) RCBS ladle dropped the alloy
temperature 25 degrees, and it was simple to determine when the
temperature recovered prior to beginning the casting sequence.

Many have built their own units.  It’s a relatively simple design and all
the necessary parts are readily available on eBay, Amazon and/or
several suppliers for $50 to $100.  You’ll need the main controller,
solid state relay (SSR), heat sink, appropriate thermocouple, on/off
switch, fuse/fuse holder, terminal strip, power cord and small project
box.  All of this is discussed on numerous Internet sites and in several
threads on the Cast Boolits forum (
com/forum.php).  Run a search for “PID controller”.  BTW, the
controller pictured in the photo was purchased from a company which
is no longer in business.  For those that don’t want to bother with
building one, I understand there is a fellow that frequents the Cast
Boolits forum that sells PID controllers.

In closing I’ll leave you with a few comments.  The benefits of using a
PID depends on what you’re casting for.  If your pot has a bottom pour
feature and you are using it for casting handgun bullets I doubt a PID
will provide any noticeable benefits.  But if you're ladle/dip casting for
match grade bullets I think it's an excellent idea based on how well it
works for me.  Most of my casting has been for .40 cal (400 gr.) bullets
using a RCBS bottom pour pot, but I don’t use the bottom pour
feature.  I “dip cast” with a ladle.  I also have a 20 lb lee pot and use
it with a ladle and different alloy for .45 cal bullets.  The PID is
switched from pot to pot.    Not only does the PID control the
temperature very well within a few degrees it also indicates when
your pot is up to casting temperature.  A Lee pot uses a very basic
temp switch that allows relatively large swings in the alloy
temperature.  It works for many but in my estimation there’s room for
improvement when casting match grade bullets.

BTW, if you are considering purchasing an expensive pot, you can save
a bunch of bucks by going with a Lee pot and using a PID.  The
combination will result in a casting setup that provides much better
temperature control than available with expensive
 pots.  Plus you gain the benefit of precise visible feedback
of the alloy temperature while casting.  But don’t expect the addition
of a PID to significantly improve results if your casting technique is
poor.  Precisely controlling the alloy temperature is only one of several
factors affecting cast bullet quality.  For more details on reducing the
weight variance of BPCR bullets go to:

Wishing you great shooting,
Updated 6/10/18

Since writing the article below RCBS and Lyman have introduced
casting furnaces with PID controllers built in.  The RCBS ProMelt 2,
RCBS Easy Melt and the Lyman Mag 25 feature easy to program and use
PID feature.  The RCBS ProMelt 2 and Lyman Mag 25 are bottom pour
designs but can also be used for ladle dipping.  The RCBS Easy Melt
model for ladle dipping only is an especially good buy.  All hold 25 lbs
of alloy.  To read a full evaluation of the RCBS Easy Melt furnace click
Evaluation of the RCBS Easy Melt Casting Furnace with PID.  For
more details on how PIDs work, read on.

I've been using a PID controller when casting since Aug. 2015.  It’s an
electronic device that is installed in-line with the AC power to the
casting pot.  No modifications are required to the pot.  The PID
controller (hereon referred to as a PID) plugs into AC power and the
pot plugs into the PID.  A thermocouple connected to the PID is either
installed in the pot prior to adding alloy or inserted into the alloy after
it has sufficiently melted.  The thermostat on the pot is turned to
maximum temperature and the PID takes over control of the power to
the pot to finely manage the temperature.  After it was calibrated
(“trained”), which was a simple step, it held the alloy temperature of
my 22 lb capacity RCBS Pro-Melt casting pot to within +/- 5 degrees of
the set temperature during the normal casting sequence.

Following is a photo of my setup.  You will note the PID in the center
of the photo and the thermocouple inserted into the alloy.  Also note
the temperature is set for 750 degrees (green readout) and the actual
alloy temperature is 751 degrees (red readout).