An interesting simple casting experiment

Talk with other Shiloh Sharps shooters.

Moderators: Kirk, Lucinda

Post Reply
TexasMac
Posts: 2364
Joined: Sun Nov 04, 2007 5:29 pm
Location: Central Texas
Contact:

An interesting simple casting experiment

Post by TexasMac »

I knew that the alloy temperature affected bullet weight but had never determined how much. Normally I went with the temp that resulted in fully filled out bullets using a specific alloy. Since I planned to cast sufficient bullets for 3 silhouette matches I figured I’d run a simple experiment. So I just finished casting & weighing 3 batches (60 bullets/batch) of .40cal 400gr bullets using the BACO 409400M5 (old 409400M4) mould and the RCBS Easy Melt PID controlled furnace.

The 1st batch was cast at 765 degrees & weighed 400.0grs +/- 0.6grs. The alloy temp. was increased to 770 degrees for the 2nd batch which weighed 401.0grs +/- 0.3grs. So then I lowered the alloy temp. back to 765 degrees for the 3rd batch with dropped back down to the same weight as the 1st batch (in this case the weight was 400.0grs +/- 0.5grs). So now I know that 5 degrees will result in a change of approximately 1gr.

BTW, the alloy was verified as 15.7:1 by measuring the specific gravity using a laboratory grade high precision scale.

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
Gamerancher
Posts: 199
Joined: Mon Sep 19, 2016 4:29 pm
Location: Central NSW Australia

Re: An interesting simple casting experiment

Post by Gamerancher »

Wayne, have you verified the actual temperature that that furnace is running at.
I have the same furnace but when I first got it I had problems with bullet fill in my mold. I had it set at 400 degrees C. ( 752 deg F )
After checking it with the probe from a custom built PID that I already had, I found that I had to dial it up to 440 C to get it to measure 400 C.
After that, I was able to cast perfectly formed bullets using the RCBS unit. Maybe it's just mine, but that is a 10% error.
Out in western NSW where it don't rain much.
Australia
Michael Johnson

Re: An interesting simple casting experiment

Post by Michael Johnson »

Wayne, it would be interesting to extend this experiment and shoot a ten shot group of each temperature range at two separate 300 yard targets with the same sight settings. See if it makes a difference. - Mike
TexasMac
Posts: 2364
Joined: Sun Nov 04, 2007 5:29 pm
Location: Central Texas
Contact:

Re: An interesting simple casting experiment

Post by TexasMac »

Gamerancher wrote: Fri Mar 29, 2019 5:07 pm Wayne, have you verified the actual temperature that that furnace is running at.
I have the same furnace but when I first got it I had problems with bullet fill in my mold. I had it set at 400 degrees C. ( 752 deg F )
After checking it with the probe from a custom built PID that I already had, I found that I had to dial it up to 440 C to get it to measure 400 C.
After that, I was able to cast perfectly formed bullets using the RCBS unit. Maybe it's just mine, but that is a 10% error.
Yes I have. Once the temp reaches the set value & stabilizes it's within a few degrees. When the PID was set at 765 degrees the measurement with a digital meter and thermocouple probe indicated the actual alloy temp ranged +/- 3 to 4 degrees of the set value. BTW, you may be interested in reading a full evaluation of the furnace I wrote & posted in June of last year shortly after they were introduced. Here's the link: http://www.texas-mac.com/Evaluation_of_ ... h_PID.html

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
TexasMac
Posts: 2364
Joined: Sun Nov 04, 2007 5:29 pm
Location: Central Texas
Contact:

Re: An interesting simple casting experiment

Post by TexasMac »

Michael Johnson wrote: Fri Mar 29, 2019 5:21 pm Wayne, it would be interesting to extend this experiment and shoot a ten shot group of each temperature range at two separate 300 yard targets with the same sight settings. See if it makes a difference. - Mike
Mike,

Considering the average weight change was only 1gr due to the temp. change and the weight variance within each batch was about the same or slightly more, I would be very, very surprised if it would make a difference. I'm not in the least bit concerned about the 1gr average change. I ran the experiment to see what would happen & was surprised to measure the 1gr average change. BTW, one result, the tightening of the weight spread at the higher temp, may be an anomaly or within the statistical variance of the experiment. I plan on casting 3 more batches using a different mould with the same bullet weight & will vary the temp to see if the results are the same. I'll post the results here.

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
Michael Johnson

Re: An interesting simple casting experiment

Post by Michael Johnson »

I doubt if it would make a difference either. I think it is important to allow the mould as well as the melt to get to temperature. Stay in a consistent cadence, use the same alloy, etc, etc.What your experiment does show is that temperature difference varies the weight of the bullet; larger temperature variance will most likely result in larger bullet weight variances. - Mike
clearcrickshooter
Posts: 190
Joined: Sun Mar 18, 2007 9:23 am

Re: An interesting simple casting experiment

Post by clearcrickshooter »

Since I have moved into a heated/cooled temperature controlled room(from cold or hot garage my casting weights have stabled dramatically,which I am sure most of you have found out. As far as casting temps,I have a set temp. that I cast all my bullets at and I never change the thermostat.
Coltsmoke
Posts: 1513
Joined: Sun Jul 04, 2010 8:55 am
Location: GA.

Re: An interesting simple casting experiment

Post by Coltsmoke »

How does a higher temp. cause the bullet to weigh more if the bullets cast at both temps. were completely filled out? I'm not trying to say that they don't weigh different, I'm asking how does it happen. If both batches of bullets are completely filled out and both batch of bullets have the same size bands, .409 where the bands are supposed to be .409 and both bullets measure .409 at the same bands, how is one bullet heavier than the other? The alloy in the pot has to change some how or something takes place, what is it? Can't be the higher heat causes the mold the change, you would have different size bullets, it has to change the melt somehow.
Normal isn't coming back, but Jesus is.
Michael Johnson

Re: An interesting simple casting experiment

Post by Michael Johnson »

I would postulate that a 1 grain variance in weight is undetectable visually. - Mike
TexasMac
Posts: 2364
Joined: Sun Nov 04, 2007 5:29 pm
Location: Central Texas
Contact:

Re: An interesting simple casting experiment

Post by TexasMac »

Coltsmoke wrote: Fri Mar 29, 2019 8:13 pm How does a higher temp. cause the bullet to weigh more if the bullets cast at both temps. were completely filled out? I'm not trying to say that they don't weigh different, I'm asking how does it happen. If both batches of bullets are completely filled out and both batch of bullets have the same size bands, .409 where the bands are supposed to be .409 and both bullets measure .409 at the same bands, how is one bullet heavier than the other? The alloy in the pot has to change some how or something takes place, what is it? Can't be the higher heat causes the mold the change, you would have different size bullets, it has to change the melt somehow.
No doubt the increase in alloy temp results is the mould being slightly larger, therefore the bullet is slightly larger in all dimensions. But a 1gr difference is not detectable visually or even with vernier calipers. Keep in mind that the weight variance of a batch of bullets can easily exceed 1gr when they are all cast at the same temp.

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
TexasMac
Posts: 2364
Joined: Sun Nov 04, 2007 5:29 pm
Location: Central Texas
Contact:

Re: An interesting simple casting experiment

Post by TexasMac »

Michael Johnson wrote: Fri Mar 29, 2019 7:25 pm I doubt if it would make a difference either. I think it is important to allow the mould as well as the melt to get to temperature. Stay in a consistent cadence, use the same alloy, etc, etc.What your experiment does show is that temperature difference varies the weight of the bullet; larger temperature variance will most likely result in larger bullet weight variances. - Mike
Mike,
I certainly agree with you & it's one reason I started using a PID to control the pot temp a few yrs ago and more recently bought the RCBS pot with built-in PID. I think we generally all agree that a change in alloy temp will have a direct effect on bullet weight. The question is how much does it take to make a significant difference? Certainly that depends to some extent on the shooters ability among other factors.

Knowing that 5 degrees of alloy temp makes a change of 1gr with a 400gr bullet, will a change of 25 degrees result in a 5gr change? I don't know & I'm not concerned enough to experiment further. Does a PID controlled pot make me a better shooter? From my perspective it minimizes one source of error and increases my confidence in the bullets I cast, which is a good enough reason for me to spend the extra bucks. BTW, it also makes changing alloy temp a precise amount real easy.

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
bruce m
Posts: 3350
Joined: Tue Aug 04, 2009 5:25 am
Location: australia

Re: An interesting simple casting experiment

Post by bruce m »

wayne,
there is no doubt you have an enquiring mind!
if you slow the casting rate a little, will the mould run a little cooler and the weights of the hotter alloy bullets reduce to that of the bullets cast at the lower temp at the normal rate?
bruce.
ventum est amicus meus
TexasMac
Posts: 2364
Joined: Sun Nov 04, 2007 5:29 pm
Location: Central Texas
Contact:

Re: An interesting simple casting experiment

Post by TexasMac »

bruce m wrote: Sat Mar 30, 2019 6:16 pm wayne,
there is no doubt you have an enquiring mind!
if you slow the casting rate a little, will the mould run a little cooler and the weights of the hotter alloy bullets reduce to that of the bullets cast at the lower temp at the normal rate?
bruce.
Hi Bruce,

I do plan on running the same experiment during the next casting session of 3 batches of bullets from a different mould to see if the results are similar. But other than that I’m not curious enough to experiment further. I’ll leave the casting rate experiment for you to carry out. I’m betting that slowing the rate will also lower the average bullet weight.

Wayne
NRA Life (Benefactor & President's Council) Member, TSRA Life Member, NSSF Member, Author & Publisher of the Browning BPCR book
http://www.texas-mac.com
bruce m
Posts: 3350
Joined: Tue Aug 04, 2009 5:25 am
Location: australia

Re: An interesting simple casting experiment

Post by bruce m »

wayne,
you've got me on that one :lol:
I intend to just keep going how I am.
it all gets too hard.
I do admire your approach and read your stuff with great interest.
bruce.
ventum est amicus meus
Post Reply