air temp and bullet hardness

[glock3540]

How much, or does air temperature effect the hardness of a cast bullet.  The reason I ask is because my casting set up is in an unheated shed.  Will the bullets that I cast in the summer be softer than the ones casted in the winter since they will take longer to cool down.

[Fireball 57]

glock:  The outside temperature after casting your bullet will have little to do with the hardness of the cast bullet.  To qualify the last statement, if cast bullets are dumped in cold water immediately after casting, wheel weights seem to be harder than dumped on a towel to air cool.  Wheel weights cast into pistol bullets are generally, hard enough with air cooling to not lead quality revolver barrels.  Auto pistols are subjected to magazine loading and May require dumping immediately in cold water, after casting to increase hardening.  Be careful, 700 degree molten lead will leave permanent scarring!  regards :wink:

[Leftoverdj]

How much, or does air temperature effect the hardness of a cast bullet.  The reason I ask is because my casting set up is in an unheated shed.  Will the bullets that I cast in the summer be softer than the ones casted in the winter since they will take longer to cool down.

Might make a theoretical difference, but not a practical one. Too many variables at work to be able to isolate that one. Gun don't really care of the bnh hardness is 10, 11, or 12. Bigger spread would make a difference, but it would have to be a pretty sizable one. You can get that much of a spread from alloy, temperature, and aging variations.

I'm gonna get up on my soapbox here and say that many casters, especially new ones, get wrapped up in minutia. Standardize your alloy, learn your mould preferences, keep a steady rythmn, and you'll get good bullets. Learn the limits of those bullets, and you'll be all right. Time enough to get into minutia when you start shooting benchrest or high (for cast bullets) velocity.

[stuffit]

I'm not so sure this factor won't make a significant difference in bullet hardness.  I haven't tested it scientifically and I cannot remember seeing it authoritatively spoken to by someone who really knows.  Water cooling or heat treating/water-cooling can make a drastic difference in bullet hardness.  This fall is the first time I've done much casting in cooler weather (which actually isn't all that cool here in MS), but I found it remarkable how much faster the bullets cooled to a temperature at which they could be manually handled in contrast to a seemingly infinite time when casting in summer (which is really hot here).  Maybe talking about an air temp difference of 40 degrees or more.  I suppose I thought of this when my goal was to get some softer (Br 11 or so) bullets for some PB 45-70 bullets for mvl in the 1400 fps +/- 50 - 100 fps range;  and maybe some a little softer.  Anyway I cut my alloy with lead Xray shielding and still didn't get the decrease in hardness I wanted.  So I got to wondering if the air temp could be a significant factor and I still do.  I did mention pondering on this on another forum where there are many knowledgable bullet casters and no one uttered a breath about it.  From past experience there, that usually means they don't know.   Some controled casting on this might just be interesting.

While I agree that we can sometimes get bogged down in "minutia" , sometimes attention to generally overlooked details can make a significant difference in a process or product.  It's an interesting query and no one seems to really know.
 :wink:
stuffit

[Leftoverdj]

Stuffit, here's what I do know. Water quenching raises the hardness of my alloy 6 bnh points. That's cooling 600 degrees in a second or so. I have never been able to reach into the bucket fast enough to feel remaining warmth in the bullet.  Air cooling to the point that I can pick them up takes several minutes in any weather. You can cast in 110 degree temp or in 20 degree and it's still gonna take minutes rather than seconds.

[Harry O]

Not exactly an answer, but I cast three different bullets from the same melt at the same time a while back.  All were dropped onto a pile of towels at an air temp of about 65 degrees.  I later tested the Brinell hardness of them.  The heaviest one was 267gr and tested at 17.6Bhn.  The one at 185gr tested at 18.2Bhn.  The lightest one at 98gr tested at 19.3Bhn.  I figure the difference in cooling between the light and the heavy made the difference.  Mixture of the melt and temperature was the same for all of them.

I figure the small ones cooled much quicker (similar to quenching).  The heaviest ones cooled much slower (similar to annealing).  I can verify the time it takes to cool by how long it took before I could pick up the bullet with a bare hand.

[cbrick]

Interesting thread. From my own experience in heat treating various bullets for long range handgun your all more or less right.

Different weight bullets cool at different rates and does affect the final BHN. This is the reason ingots should not be tested with a bullet BHN tester. A 1 pound ingot will cool much slower and the final BHN will be much softer than a 200 gr bullet cast from the same ingot.

Different BHN bullets with the same load (bullet, charge, crimp, primer etc) does change the group size, velocity and standard deviation. For examples: My FA 357, RCBS 180 gr silhouette, 14.6 gr H-108, CCI 550 primer, all tests with virgin WW brass.

22 BHN bullets
Extreme Spread - 25
Average Velocity - 1455
Standard Dev. - 8

18 BHN Bullets
Extreme Spread - 18
Average Velocity - 1495
Standard Dev. - 6

Both tests fired on the same day and all components from the same lot numbers.

Other cartridges show even more variation with no change other than Bullet BHN. In this FA 18 BHN gives both the highest velocity and the best groups. The further from 18 BHN in either direction the worse the groups and the slower the velocity.

BHN's within a range shows no variatoin on the chronograph. Example 14-15 BHN. 17-18 BHN. 21-22 BHN.

So to answer the original question in this thread. Yes, air temp probably does affect the final BHN BUT, my air cooled WW alloy is 11 BHN, if I cast outside on a cold day and they turned out 12 BHN there would be very little to no difference in how they shoot.

My 2 cents worth from my experimenting. Hope this helps.

Rick