SSS -  I've got one of those.  SOMEDAY I'll hook it up!  (round tuit syndrome)

Big block - little block --> temperature stability.  Good of  you to note that.

Cat: the spout of ladle is stuffed tight into the sprue hole during the pour.  Then I tilt it slightly so to release any air build up (you'll see bubbling), count 5 seconds and then create the sprue puddle.  Again, depending on the weight of the bullet, the frost time is the next critical step ... up to 10 seconds for bullets greater than 500grs.

The scale is from Deal Extreme in Singapore with free shipping ... (You need to Login or Register to view media files and links)
For a cheap digital, it has an excellent strain gauge that governs the quality of the read outs, repeats constant weights with no fluctuation and is dead nuts accurate.  Have verified using a beam balance scale with calibration weights and on the digital also  

Quote:
Cat - the pot melt and mold temperatures have to be the same to create a puddle melt that are equal for a minimum 5 second frosting time.  I also spread the puddle on the sprue plate to help maintain a constant temperature of the plate.  Remember all molds heat differently so bring everything up to the temperature so the minimum frost time is 5 seconds.

If one doesn't wait for the the puddle to frost and then cut the sprue... you will have a hot coating of lead on top of the mold halves.  Then you are in deep doo - doo!

Cat,

The interesting thing about your graph is that the weight goes up and down after you get into the main casting session.  I get essentially no variation during the middle of the casting session unless I stop to rest my hands or add lead.

I start with my mold heated on a hotplate.  Will still get about 5 or 10 that weigh lighter.  Then, the weight stabilizes, and is very consistent.

I cast about 135 to 150 bullets at a time with the goal of keeping 120 that are within .1 grains + - of each other.  I lay the bullets out in order cast.  I do a row of about 30 at a time, then stop and add some lead to the pot.  I keep the mold on the hotplate while stopped.  My technique is to use a lee 20 pound pot, lyman ladle.  I hold the mold horizontal, dip the ladle, pour a bit out to clear dross from the spout, and then put it to the sprue plate and tip the mold and ladle up.  Hold for a count of 3, then pull the ladle away and pour a puddle on the sprue plate.  Count to 8 and the sprue should be frosting over.  Wait another 4 count, cut the sprue over the pot and let it fall back in.  Open the mold over a towel, and the bullet falls out.  I then pick up the previous bullet cast and place it in the row in order, leaving the just cast bullet to cool a bit before I pick it up.  This whole process of dropping the bullet and moving the last one gives me about a 10 count for the mold to cool slightly before the next cast.

Using this technique, I can usually get 100 to 120 bullets within .1 grain of the median weight from a batch of 135 to 150.  I usually reject about 10 at the beginning that are light, and about 3 to 5 when I add lead to the pot.  Other than that, I reject maybe one out of 20 that is light for some reason, I presume voids.  Occasionally visually discard one also.

The mold matters in this.  I can hold .1 grain with 375 and .32 molds I have.  My favorite .458 540 grain holds only .2.

dave

Gents - for the Good of the Order:
I don't use a PID but maybe one of these years.
Anyway, I use a Tel-Tru BIG Green Egg, Primo, Grill Dome, Kamado Replacement Thermometer LT225R ... (You need to Login or Register to view media files and links)
It is accurate and  can be re-calibrated by adjusting the dial. Every once in a while, I stick it in a pot of boiling water with a digital thermometer also in the pot. The temperature on the digital compared to the Tel-Tru was only once out of adjustment by a few degrees a couple of years ago ... and I have been using this same Tel-Tru for close to 10 years

Cat_Whisperer wrote on Nov 24^th, 2013 at 9:02am:


They sell them here:
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Cat, do a batch of bullets with a 5 second (count 1-2-3-4-5) pour and a 5 second frost ... and then let's see what your bell curve looks like. A MUST - Be Consistent with Your Casting Rhythm