Monitor Your Cooking Time

[slide]

I guess I am lucky. I have a powder coat mfg. about 10 miles down the road. The guy who is the quaility control manager has become a friend and a fellow shooter. One test that he recommends is called the cross hatch test. I won't say how to do it but if you are interested look it up. He says the hammer test can be misleading. In his lab we under cured some coating and cured some the right way. Both showed the same results with the hammer test. Powder coat has a certain strength to it. When you fire a powdercoated round the rifling bites into the powdercoat. If it is not cured right the bite won't hold like it should. If it is undercured or overcured it will affect accuracy. I was a competitive shooter for 18 years and one thing I learned was that little things can make a big difference. Dragonheart,I have a proposal for you. From now on neither of us will mention anything about the thermocouple method. Most guys are doing it their way and refuse to change and that is fine. Everytime it is mentioned you might have one or two that like it but for the most part it is,you didn't come up with that so and so did. The main response is I throw them in the oven and walk away. I for one am tried of it.

[Dragonheart]

Slide, as I first mentioned I made this post because the same curing question keeps coming up and a thermocouple is a sure fire way to solve the problem. I do realize most will blow it off and continue with what they are doing and I think we both agree that's fine, but some will give it a try and be better off for doing so and those are the one's this post was intended for. if we don't continue try to help others then what is the purpose of this site? I didn't invent the thermocouple, thermometer or the internet, but I have learned to use them all as well as a lot of other things and I am more than willing to share what I have learned with those who want to listen. For those that don't that's okay too, because my ego doesn't need a boost. But one thing most will agree on is when someone is trying to help nobody likes being made sport of.

Most are probably not aware of this but I was the first to post here about using silicone mats to cook on. As you can imagine those that had always used foil, parchment or whatever chimned in. But the message got to some that were willing to at least give the silicon mat a try and now those are singing the praise of the silicon mat. And I will state this as I did in my original post the silicon baking mat was NOT MY IDEA! Cooking bullets on a silicon mat was actually my wife's idea because she got tired of looking for her non-stick aluminium foil in my garage. So she said, "here use these silicon mats instead, they are non-stick and good to 500 degrees". Well the rest is history.

You also mention some good points and that so many just don't seem to get no matter how it is said or how many times. The rifling approximately .004" deep and it indeed bites into the powder coating. If the coating is thick enough and properly cured the polymer jacket will have a slick, hard, elastic and a tenacious bond to the alloy. An old retired PHD professor of Polymer Physics calculated a .003" polymer build out would sustain the torque spinup of a 30/06 with 50K chamber pressure. The polymer is more than just a lube as so many think it is a polymer jacket. And this polymer jacket can perform all the duties required of a jacket for accurate full power loads, but to do this it needs to be properly applied and cured and here we are back at a thermocouple at least for the latter.

[slide]

Yeah, I guess you are right about helping. If you remember I sent a pm to you asking about shooting cast in an AR. I have been on that quest ever since. Sometimes it gets aggravating especially when you fail and then get flamed on here for no reason. I have two mottos that I try and live by. Nobody takes anything that is mine and I don't like being called a liar. I was really lucky to find my buddy. He is really excited about shooters using powdercoat to coat their bullets and we are working on some new stuff that may break this whole deal wide open. Time and testing will tell.

[Dragonheart]

Slide, I wish you all success in the goal of rifle accuracy at distance with full power loads. i personally have put that quest on the back burner until I can come up with a reasonable" economical way" to Swage or Re-align cast bullets to make them concentric. If that can ever be achieved and with PC it most definitely will bring bullet casting into a new era. But until then the lopsided cast bullets will only be suitable for low velocity or short range full power.

[blikseme300]

I looked into Tempilaq and was told it had a 1 year shelf life and I never went any further, because I go in spurts where I cast. I cast and coat tens of thousands of bullets and then I may go a long time before another spurt, but it sounds like a really good idea. I already had the digital thermostat and several bare K probes I purchased in 2012, so no additional outlay wasn't required.

I store my Tempilaq along with bulk cyanoacrylate in my beer fridge, which is set to the proper temperature that will freeze sodas. I have done random tests and the 5 yo CA glue and the Tempilaq works as welL as fresh purchases.

[midnight]

I just read this whole thread and a question occurred to me. Maybe someone can explain it. I see folks attaching various bullets to the end of a temp probe to measure when the interior of a lead bullet reaches the required temp. Why do I have to know the interior temp of a bullet when all the curing of the powder is occuring on the surface of the bullet?

Bob

[slide]

When I came up with this idea I kinda wrestled with the same question. I taped the thermocouple to the outside of the bullet with high heat aluminum tape and then drilled a hole in the base of the bullet and tried that. I really couldn't tell a difference in the temp readings. The only thing I did discover working with the inventor ( Hi-tek Joe) of hi-tek coatings was that a coated bullet will absorb heat at a different rate than a bare bullet. I always use a coated bullet of the same caliber I am baking. Try it both ways and see which one you like.

[Dragonheart]

I just read this whole thread and a question occurred to me. Maybe someone can explain it. I see folks attaching various bullets to the end of a temp probe to measure when the interior of a lead bullet reaches the required temp. Why do I have to know the interior temp of a bullet when all the curing of the powder is occuring on the surface of the bullet?

Bob

The heat transmission rate for lead is actually quite fast since the transmission is only having to travel fractions of an inch, but what we have to consider is the time it takes to bring a mass (the dynamic load) up to temperature. Because the greater the mass the more energy it takes to bring that mass up to temp. If the mass is increased you have to either increase the energy output or increase the time. In our ovens the BTU output remains pretty much constant, if the thermostat is working properly, so we need to add more time, but how much? If you don't know you guess, and this is what the thermocouple is all about. It tells you that in a specific spot the temperature of the metal itself has reached a certain temperature.

When I cook 4 or 5 trays with each tray holding over 1000 bullets I use two or three thermocouples cast in bullets placed in the middle of the trays. i don't start my timing until all the thermocouples come up to 400. Even with two 220V elements maintaining 400 degrees air temperature you might be surprised how long it takes 4-5K of 9mm bullets to absorb the energy and come to 400 degrees. A bare thermocouple wire is laying in a tray would be doing what an Oven Guide Thermometer does, it would be measuring the air temperature.

[midnight]

I only coat one tray at a time. Even with a tray full of 9mm bullets (about 250) I notice that it only takes about 15 seconds for the powder on the center bullets to flow, after the outside ones flow. I preheat my oven to 450 while I load the tray, put the tray in the oven & turn it down to 400. After flow, set timer for 20 min. Always works for me. Just did about 800 this afternoon. Used Eastwood's Ford blue & turquoise. Both have been reliable, along with red wagon.

Bob

[slide]

Do whatever the mfg. recommends and you will be ok. I have noticed that Eastwood does the 20 minutes after flowout. If it ain't broke don't fix it. Good luck!

[Black Jaque Janaviac]

I get that you want to make sure the powder gets up to temp and remains there long enough to cure - but is there much danger in exceeding the cure time if the temp remains a constant 400°?

I spread the bullets out in a single layer, and give them 30 minutes and none of my bullets are larger than 225 grains (most are 125). I often forget or get wrapped up in something else and have left some in for a couple hours. I can't say that I've experienced any problems with leading except when developing a full-magnum load. I just assumed I reached the limits of powder coating.

[slide]

Most powders have overbake resistance. This means they can stand spikes in temp but won't handle staying at too high of a temp. The powdercoat becomes brittle when it is overbaked. I am going to do some testing later on with powdecoats cured right and some that are overbaked and underbaked. If what you are doing works for you then by all means keep doing it. It is just as easy to bake the bullets with a thermocouple. I have done it so much I know when the temp is getting close. I will then sit down and keep an eye on it. I am 69 years old and a break is welcome.

[Dragonheart]

If it will ease some minds or save some a little time they could be putting on more useful projects I will tell you I have already experimented with extended an extended cooking time. I would also like to tell you I planned this out considering every detail, but the fact is I screwed up.

My 30" oven is controlled with a PDI, so it typically will stabilize within a degree or so. When I built the oven i put a switch on the digital timer so I could take the timer in or out of the circuit. I did this because I use multiple thermocouples and I let the PID bring the oven air temp up to 400 degrees and hold it there until all my thermocouples indicate the multiple trays of 1000+ bullet per tray come up to temp. Then I flip the switch, the timer gives it 15 minutes and cuts off while I usually leave to do other things.

Well one evening everything was up and running with 3 trays in the oven when the phone rang and a neighbor wanted us to join them for dinner. Maybe I was tired, or maybe I was hungry, or maybe I was over 70 and got distracted, but the long and short is I didn't flip the switch before I walked out the door, so the timer never started the timed bake.

The next day when I walked into the garage I immediately noticed it was warmer than usual. A quick look at the oven lights confirmed it was still on and the PID was reading 400 degrees. The PID had done its job for the last 18 hours!

I was a little distraught as there was in excess of 3000 bullets in the oven and I knew that was a really long cooking time. When I opened the oven door, let it cool down and started inspecting the 3K of H&G #68 45 ACP bullets they looked as beautiful as ever, but instead of being a "Tractor Green" the had a darker green color I would call closer to Army Olive Green, but the coating was well bonded, and when sized, loaded they shot without a problem.

I can't say this was a controlled experiment or a any scientific evaluation took place, but the exceedingly extended cooking time bullets worked just fine in my 1911's. But note, the time was severely extended, but not the temperature as they remained at precisely 400 degrees. I certainly do not recommend an extended cooking time anywhere close to this, but it would appear at least in this one instance with low velocity handgun loads the only thing that suffered was the color. Sometimes you can walk in it and just get lucky.

[Hossfly]

I worked with Trane absorption machine chillers for about 30 yrs, we had to log the temps all over the chiller about 11-12 places. At first we used a set of lab thermometers glass of course, which wouldn’t take any abuse of course.

Until I found out about thermocouple digital thermometers, of course there was skepticism about that, till they found out they were less apt to break and cheaper in the long run. Anyway I still have the first set they paid for except they are a little shorter now.

Talked them into buying a 50’ roll of tc wire so we could make our own and the ends to go with them. Anyway when I retired after 43 yrs. that roll of wire ended up in my reloading room, what was left of it anyway.

When trying to get pc to temp, read here on CB to drill hole in boolit and place in tray with load to be baked. Worked very well, just stick end of wire and pinch boolit with hole in it to grab the coating of tc wire. Made several different ones for all that I cast.

Interesting the wire pair is of course 2 different metals, one of which is magnetic while the other is not and they go on either + or - i forget which is which, but if you get them wrong temp goes the wrong way and you just switch em around. And you just strip coating and twist and fuse together, not soldered together.

Works very well tc boolit method. This site is a wealth of knowledge.

[slide]

I like your idea of pinching the bullet. I will give that a try. I have a box full of thermocouples with different bullets on them. I usually use high heat aluminum tape. It is not pretty but it works and I can take the tape off and use the thermocouple for other things. With all the thermocouples I have I really don't change them out anymore. It really is the only way to tell where you are and I really feel like it makes a difference. I started out with hi-tek and I don't know how many bullets failed the smash and swipe test and I remelted them. One day a fella named Ausglock made a joke to somebody about sticking a thermometer up the bum of a bullet. That stuck in my brain and off we went to the races. I acutally stuck a casting thermometer in the base of a bullet but that didn't work to good. I am an old man and it was hard for me to see the dial inside the oven. One day I was drinking coffee and noticed a multi meter with a thermocouple setting on the counter. Drilled the base and taped the thermocouple in and it worked. I had no more trouble with the hi-tek coating. One thing I like about the digital thermometers the temp changes instantly even if it is 1/2 degree or less. With the oven thermometers it takes a little bit for the temp to change. A lot of people use them and like them and that is ok by me. I know what you mean about skepticism. Seems like a lot of people won't accept the thermocouple method and some get downright rude about. Good luck!