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Thread: Are 2nd coats worth doing?

  1. #21
    Boolit Bub
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    Redeemed myself today. Added some plastic pellets in with the shake of light ford blue, and stood a couple hundred or better up on their base, baked at the 400 for 25 min.
    Came out great very happy. This is a .401 10mm BB RCBS mold.
    Just hav e to take the extra time to stand them up, already spending a lot of time in the whole process.. might as well spend another 20 min get good results.
    These still need sized of course.
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  2. #22
    Boolit Master
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    I had my first experience with 2nd coats this past week. I had done a poor job achieving coverage (very thin PC for some reason) on some Accurate 36-125L and they weren't grouping well... everything went to heck when I exceeded 1350-1400fps. A second coat got me to between 1600 and 1700fps. Totally worth the effort to save those batches of boolits.

    Have never needed it before, makes me wonder if I should try it on others and see what happens to the accuracy and velocity ceiling...
    I'm a big fan of data-driven decisions. You want to make me smile, show me a spreadsheet! Extra points for graphs and best-fit predictive equations.

  3. #23
    Boolit Bub
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    Yes I knew it was something I didnt want to do every time with a 2nd coat. Just had that first batch attempt with poor results and was trying to salvage them, was kind of looking for results of someone that had done it. The batch above was one the one and only coat course.
    Interesting to hear the velocities. Ive not cast for rifle rounds yet, I have a 308 I want to reload with. I forget at what the velocity limits are on cast bullets, need to look into it again. Never really considered what they are with PC.

  4. #24
    Boolit Buddy
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    For best temperature control for baking I suggest a convection toaster oven and a PID. (Check the acronym sticky if you don’t know what a PID is)
    NRA Lifetime member since 1956, NRA Endowment Member. Reloading since 1954. CBA Member Navy Vietnam Veteran USS Intrepid CVA 11

  5. #25
    Boolit Master
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    When I saw this post I just had to leave a comment. Hopefully this will help some first starting and if you need information on PC there are a lot of good posts available here, of course some not so good either.

    First that clown on YouTube has set powder coating back to way beyond when I first started PC in 2012. Even back then every powder manufacturer stipulated a cure schedule of 10 minute minimum at 400° for standard powders. That 10-minute cure time does not start when you turn the oven on, when the powder starts to flow at approximately 150° or even when the oven thermometer or PID reaches 400°.
    The timing starts when the load (bullets) surface temp reaches 400°. The load is absorbing energy so it has to equalize, this may taky a few minutes or closer to an hour depending on the load, oven, power, etc. etc..

    When I coat 5-6K bullets at a time my two 230V heating elements will bring the oven air temperature in my PID controlled oven up to 400° in approximately 12 minutes and hold it to within a couple of degrees. But realize a PID is only controlling the air temperature in the oven, something you can do with a good glass thermometer in a well-sealed oven with a good thermostat. However, once my oven air temperature reaches 400°, it will take an approximate 35-40 minutes more for all the load (5-6K bullets) to equalize and reach 400°.

    I monitor the temperature of the bullets with a couple of inexpensive thermocouples. Similar to this one found on here Amazon "Digital Thermometer Dual Channel Thermometer Temperature Thermometer with Two K-Type Thermocouple Probe Backlight LCD K Type Thermometer for K/ J/ T/ E/ R/ S/ N"

    I simply cast the end of the K-type probe wire into a bullet then lay the bullet/probes in a tray with the other bullets. This is the most accurate way I have found to monitor the temp and assure full PC cure.

    I do double coat full power rifle bullets to increase the polymer thickness. Handguns do not come close to rifle velocity’s and single coating has always worked for me.

    BTW: Eastwood came up with the “start your cure timing after powder flow”, which is just more bad information. Eastwood is a retailer, not a powder manufacturer. That method may work if you are coating a motorcycle frame and once the powder shines you are happy, but PC shine does not indicate full cure, and is altogether different if you are depending on full cure of the polymer prior to loading it to 3600 FPS or 50K pounds of chamber pressure!

  6. #26
    Boolit Master
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    Single coating rifle bullets work just fine. I've tested the .308 at 2400fps with no issues or even a hint of an issue with the PC or leading. Many others have gone faster.

    I coat a much smaller quantity of bullets in my toaster/convection oven. Bullets are stood on their bases, approx 1/2" apart from each other, about 80 per load. The 'flow' guidelines that Eastwood specifies, or the total 20min cure recommended by Smoke, work fine for me. I am satisfied that when the air temp in the oven is at the desired temp, then a couple of minutes is all that is needed for the surface of the bullets to be at that same temp. I usually set the timer for 25min total. The extra 5 min is for me to be confident the oven is back up to temp after opening the door (yes, I have timed it with an accurate oven thermometer).

    If you do large batches like Dragonheart, then you need to monitor the temp of the center of your batch of bullets as he does. Takes a long time for the heat transfer to reach that point, even with a forced convection oven.

  7. #27
    Boolit Master
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    Quote Originally Posted by charlie b View Post
    Single coating rifle bullets work just fine. I've tested the .308 at 2400fps with no issues or even a hint of an issue with the PC or leading. Many others have gone faster.

    I coat a much smaller quantity of bullets in my toaster/convection oven. Bullets are stood on their bases, approx 1/2" apart from each other, about 80 per load. The 'flow' guidelines that Eastwood specifies, or the total 20min cure recommended by Smoke, work fine for me. I am satisfied that when the air temp in the oven is at the desired temp, then a couple of minutes is all that is needed for the surface of the bullets to be at that same temp. I usually set the timer for 25min total. The extra 5 min is for me to be confident the oven is back up to temp after opening the door (yes, I have timed it with an accurate oven thermometer).

    If you do large batches like Dragonheart, then you need to monitor the temp of the center of your batch of bullets as he does. Takes a long time for the heat transfer to reach that point, even with a forced convection oven.
    I do not double coat to prevent leading as a proper coated and cured single PC does that quite well and I single coat all handgun bullets.

    I double coat rifle bullets to increase the build out to approximately three mills to prevent torque spin out on full power loads. Typical rifling is .004” groove to lands in depth. The Polymer is approximately equal and hardness to copper, but with a better bond. The build out was calculated by a PhD Polymer physicist and I have confirmed by testing the polymer will withstand 3600+ fps and 50k+ psi chamber pressure, which is the largest thing I have.

    You are correct most using a toaster over with small loads can just do a guestimate on the time assuming they have first confirmed with a reliable thermometer that their over can actually reach 400° and hold that temperature without wild swings, many of these ovens can't do that and relying on the thermostat dial is not a good idea.

  8. #28
    Boolit Master
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    I have never had an issue with 'torque spin out' with cast bullets, especially with powder coating. Just a matter of using the proper alloy for the job. So a single layer PC has always worked. I would suspect that rifling twist plays an important part in your data as well. Chamber pressure is much less of an issue when the bullet is sized properly. Bullet weight (less weight, more acceleration, less spin inertia) might be something for you to consider as well. I was only a licensed mech engineer

    I agree that any oven needs to be checked with a thermometer or converted to use PID. Both of mine have done well once I figured out the dial setting to get the right temp.

  9. #29
    Boolit Master
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    Quote Originally Posted by charlie b View Post
    I have never had an issue with 'torque spin out' with cast bullets, especially with powder coating. Just a matter of using the proper alloy for the job. So a single layer PC has always worked. I would suspect that rifling twist plays an important part in your data as well. Chamber pressure is much less of an issue when the bullet is sized properly. Bullet weight (less weight, more acceleration, less spin inertia) might be something for you to consider as well. I was only a licensed mech engineer

    I agree that any oven needs to be checked with a thermometer or converted to use PID. Both of mine have done well once I figured out the dial setting to get the right temp.
    I was only a lowly industrial engineer, so I garnished my information from an individuals who actually spent a lifetime working with Polymers. As well as my on years in achieving three Master Rifle Certifications. My father in law, also a mechanical engineer with 17 patents to his credit, had a very apt statement he used often; You can always tell an engineer. You can't tell'um much, but you can tell'um. I found that very funny, but also quite true.

  10. #30
    Boolit Master mehavey's Avatar
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    BOTTOM LINE OBSERVATION:
    If a single coat doesn't provide full/sufficient coverage, you need
    either a different powder, or a different application method.

  11. #31
    Boolit Master
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    Quote Originally Posted by Dragonheart View Post
    ....You can always tell an engineer. You can't tell'um much, but you can tell'um. I found that very funny, but also quite true.
    Yep. Working as an engineer with many other physicists and engineers was sometimes a nightmare. Managing projects was even more 'fun' with such a collection of personality types

  12. #32
    Boolit Master
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    Quote Originally Posted by mehavey View Post
    BOTTOM LINE OBSERVATION:
    If a single coat doesn't provide full/sufficient coverage, you need
    either a different powder, or a different application method.
    I do agree.

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