Finding a way to get hard PC'd boolits from regular COWW alloy

fiver

Well-Known Member
but if the base is pulling heat from the nose faster than it's giving it up to the ice, the time frame for it to cool is pretty inconsequential [wow spelled that right first try] if the goal is to have a softer nose and a harder base.
 

358156 hp

Well-Known Member
I found out later that Marshall Stanton of Beartooth Bullets went down this path several years before us. His approach was slightly different than mine, but his results were wayyy different. I've been meaning to try repeating his efforts with certified alloys to see if I could find out why his efforts were so much more successful than mine, but I ended up powdercoating softer hollowpoint bullets, and got the results I was originally looking for so I blew off the project entirely. Here's Marshalls article on what he termed "Quench Anneal" http://www.beartoothbullets.com/tech_notes/archive_tech_notes.htm/35

I used to practically live on the Beartooth forums, but fell out of it several years ago and never really reconnected. We had some really wild discussions back then.
 

Ian

Well-Known Member
Ice water will, if anything, make the noses even harder.

Stanton's success hinged on a heat sink supplying energy to the noses until the system equalized. Without a heat sink, we would have better luck quenching the front half of the bullets in warm water. I found it interesting that Stanton experienced tremendous "scatter" in the hardness numbers from week 2-6, as I found the same thing and was virtually unable to make meaningful determinations until about two months, when everything settled down and the results were uniform and distinct.
 

358156 hp

Well-Known Member
I used water that was slightly chilled. I left a bottle of water in the fridge for an hour before using. My plan was to start the bases off cool, then remove the bullets from the quench fairly quickly, after about a minute or so and let them finish air cooling with my heat sink in place, which was used in the opposite manner than one might expect by its name.
 

popper

Well-Known Member
Read the beartooth article, "This assures that the bullets will temperature stabilize at 460˚F and soak for at least one hour. Upon completion of the soak time, the basket of bullets is quickly removed from the oven and placed in the quenching pan and the insulating cap is placed over the aluminum-annealing block. See Figure 2. This allows for a 1 1/2 hour cool down period. " I'm talking just a few seconds, then air cool. That is the difference. Thermal conductivity of lead is very low, time it takes for heat to travel through lead. Bullet is a heat tank, extracting from one end depletes the other end but the process is relatively slow, not like a water tank.
The article does indicate that the terminal results would be desirable.
The other solution would be to quench the entire bullet, then use a heated plate to anneal the nose.
 

Ian

Well-Known Member
I'm talking just a few seconds, then air cool. That is the difference. Thermal conductivity of lead is very low, time it takes for heat to travel through lead. Bullet is a heat tank, extracting from one end depletes the other end but the process is relatively slow, not like a water tank.
You make several assumptions which are not correct. I made the same assumptions at first, and I think 358156HP did too, which is why we conducted tests very similar to what you are doing in hopes of achieving the same results you're after. But, we found out it don't work that way. If you take a bullet at heat-treat temperature and briefly quench the base (I took from the oven with hot tweezers and touched the base in a pan with 1/4" of water in it), the base will end up being the air-cooled hardness of the alloy and the nose will be a few BHN points harder, after the whole mess normalizes for a couple of months. Five bullets from each series I tested had BHN on either end all over the map, different from each other, some harder on one end than the other and others in the exact series the opposite, until they normalized. Then, every one of them was a consistent number on the base and nose.

If you want to to pull this off without a heat sink, quench the end that you want to be softer.
 

popper

Well-Known Member
Aligned as best I could both bullets in the NOE GC expander rig, nose to nose (FP RD style). Same pressure on both. Both got shorter, base hardened one less, ~0.005. And the base hardened expanded dia at the base less, 0.002". Both bases expanded.
 

popper

Well-Known Member
quench the end that you want to be softer. Nope. Cooked 3 175gr RD PB on the hot plate (PC cooker) for an hour. Held the base on ice cube for fast count of 5. Tested as above against untreated. All in these tests had been H.T. from the PC bake previously, same batch. Neither base expanded but test nose is distorted big time. I'll repeat the squish test tomorrow and in a few days.
 

Ian

Well-Known Member
Your conductive method of heating the bullets from one end may make a difference, but don't "nope" me until the alloy has settled in :). As I wrote previously, the precipitation hardening process was very erratic for me and the other man doing this until a few months had passed, much longer than normal alloy quench behavior. Also, use an indentation hardness tester so you have some idea what is actually going on, aside from relative numbers. I filed and tested hardness in several places to not only determine the difference, but where the difference occurred.
 

popper

Well-Known Member
Don't have a BHN tester but that is irrelevant for this. 'Standard' is 1%Sb, 0.3% Cu, 31-172C has a step on the base. Fairly soft to start. Base step is a few thous. shorter on the 'standard' after the squish. The super/undercooling phenomena takes place about a specific temperature and is controlled (small grain layers) by RATE of cooling. From physics:
CCF_000033.jpg
Takes time (the variable) to get heat from one end to the other. Verified the base is harder, now to see how far up the hardening goes with a week or so. Then on to shooting for real results.
 

Ian

Well-Known Member
Thermal resistance is a constant......however, the rate of heat transfer depends on how much heat differential there is and surface area that us in play, just like you can get more fluid through a fixed orifice in the same amount of time if the pressure is increased on the high side. Surface area in contact with quench water that I used was many times that of the base alone contacting ice as you did it. In the setup I used, the nose cooled faster than the base and thus hardened more.

If you can keep the heat in the noses via a sink, or only briefly cool the base without sucking heat out of the nose, and it all settles in in time without reversing on you, you may have figured out how to accomplish the base quench. I hope the method you are testing here works out for you, and I know some of us are still interested in making this a thing.
 

358156 hp

Well-Known Member
FWIW, I tested my bullets by filing a flat on one side and testing the sides of both ends of my sample in a "V" block using my LBT hardness tester. I used double-ended wadcutters (Lyman 358063) so that I had a reliable, repeatable way to gather my data. The sprue area of a cast bullet is more likely be a bit porous from air "microbubbles" that get trapped as air tries to escape the mould cavity as the molten alloy freezes, this would potentially affect hardness erratically. Every batch I did consisted of six bullets in the heat sink, six control bullets that got completely quenched in water the same temp as the base quenched bullets, and another six bullets that were allowed to air cool at room temperature. To keep everything on the up and up, my quenching water was kept in the refrigerator until quench time to eliminate any potential variable there as well.
 

popper

Well-Known Member
Test sample nose is ~0.005 larger than standard. It is shorter but hard to measure as the nose isn't real flat anymore.
 

popper

Well-Known Member
Tested last sample today, standard is under the bench someplace. Sample nose expanded and bent so they flew out of the press. Conclusion - it works with long bullets, just have to experiment more to nail down procedure that gives best results.
Just guessing here but as tin has lower melt temp, it may go liquidus while the bulk is still solid. Allows more of the under/super cooling than the molecular 'movement' that aids in hardening.
 

fiver

Well-Known Member
tin will melt before the rest of the alloy.
I have seen it sweat from softening the nose and have watched it bead out of alloys before they finally melt.
 

popper

Well-Known Member
Correct, ~0.5%. I did not add As to that blend.
As I don't have a BHN tester (haven't seen a need yet) and the desired results is a soft nose I can determine by other means (crush test). Pics won't do much good and measurements are difficult but evidence I give for the bent nose is it wobbles when rolled across the desk. I will continue testing, cast some more of different alloys & not PC so I can get more accurate measurements. Medical stuff is slowing me down.
 
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