??? The Effect of Curing PC VS Bullet Heat Treating

[yodogsandman]

What effect does curing powder coatings in a 400*F convection oven have on a bullets heat treated or water dropped BHN hardness? Anyone ever check?

I'm thinking that a common cure time of 15 to 20 minutes isn't enough to change it much. That the bullets don't get heat soaked long enough for much change to happen.

It seems that most casters that PC their bullets believe that the BHN returns to it's air cooled BHN after the cure. That BHN is only dictated by the percentage of lead, antimony, tin, arsenic, etc.

 

[Brad]

I haven't done testing on that. I bet some hardness is lost but not sure I would bet it was all hardness added via water dropping.

This certainly would be an interesting test.

 

[300BLK]

It would be an interesting test, but I'll bet results would be different for 22cal vs 30cal vs 35cal vs 45cal. My thinking is that the smaller diameter bullets would take the heat more quickly than the larger diameter bullets.

 

[Dusty Bannister]

I was under the impression that effective heat treat and quench would be just below the point of the alloy starting to sweat or slump. The sudden quench imparts the hardness. Where annealing or softening begins at about 300 degrees and then continues without stopping. I do not HT/Q or quench from the mold or even PC the cast bullets. Just pick the alloy and let nature take care of the details.

 

[yodogsandman]

I'd bet testing wouldn't be too difficult. Bullets wouldn't really even need to be powder coated. Just heat water quenched or heat treated bullets up again to 400*F for say 20 minutes and test the hardness for a few days.

 

[Brad]

Pretty much. Might want to test a few alloys to see how composition alters the results.
I would let the water dropped bullets rest for a week or more to settle down and reach full hardness before reheating.

 

[yodogsandman]

Yep, any test would need to start with "aged" bullets.

Now I wish I had an actual bullet BHN tester. My BHN testing system is to use a 7/16" ball bearing in a drill press at a pressure of 200 lbs and calculate the hardness. Need to use 1/4" thk, flat "hockey pucks" for that. Bullet caliber size could be a factor as 300BLK has said.

 

[Rick]

I was under the impression that effective heat treat and quench would be just below the point of the alloy starting to sweat or slump. The sudden quench imparts the hardness.

That is the correct method to get the max BHN in the alloy your using however heating to a lower temp for a minimum of one hour will still harden the alloy but to a lower final BHN. You can choose your desired BHN with a given alloy by selecting the heat.

Heat Treating of Lead and Lead Alloys - Selecting A BHN Range By Convection Oven Temperature Setting

Near the bottom of the above article is a chart listing temps from 420 to 485 (slump with the alloy used).

Hope this helps.
.

 

[freebullet]

That is the correct method to get the max BHN in the alloy your using however heating to a lower temp for a minimum of one hour will still harden the alloy but to a lower final BHN. You can choose your desired BHN with a given alloy by selecting the heat.

Heat Treating of Lead and Lead Alloys - Selecting A BHN Range By Convection Oven Temperature Setting

Near the bottom of the above article is a chart listing temps from 420 to 485 (slump with the alloy used).

Hope this helps.
.

I'd lost the bookmark to that page & was looking for it. Thanks!

Was thinking of that graph as I read this thread.

 

[yodogsandman]

Always considered that article as "the gold standard" on heat treating bullets!

 

[35 shooter]

Yodog,

I've wondered about that very thing before and kind of kept my eye on the pc threads from time to time to see if any real testing was being done.
Ben came out with the BLL formula during that time and i lost all interest in trying pc.

I would bet that bullets ht @ say 460* for an hr. and then later @ 400* for 15 to 20 min. to cure the pc coat would drop the hardness a bit.
It would be an interesting test to see for sure. If i had a hardness tester i'd be all over this, as it wouldn't be much trouble at all to experiment with.

Ok, this is just one more reason i need to get a hardness tester lol. Surely someone has tried this, but i missed it if anyone has.
I also wonder if the pc coating will make up the difference in grabbing the rifling if any hardness is lost?

Dang it, your going to have me shaking and baking now.

 

[Ian]

One of these days I'll actually test this. Not on PC'd bullets as the coating would affect the indention, but with an un-coated bullet in the batch being oven cured.

Most of the PC requires a 400°F cure time at part metal temperature for ten minutes. Some only require 340, other "low cure" coatings require even less, like around 300 but for a much longer time. I suspect on pre-hardened bullets that some annealing would take place, but probably not very much. I've "drawn" bullets down from maximum heat treat before, but used a slightly higher temperature and much longer soak time than it takes to coat.

Over cure and over bake are two things you do NOT want to do to powder coatings, particularly over bake.

 

[yodogsandman]

35 shooter, You wouldn't gain any accuracy by using "shake and bake" rifle bullets. The PC doesn't evenly coat all the bullets. Electrostatically sprayed powder coated bullets still won't provide enough consistency to equal the accuracy that you enjoy now with BLL.

"Shake and bake" pistol bullets seem to shoot fine accuracy wise, at the lower velocities. PC could also be "too slippery" to hold the rifling at higher velocities, too. I noticed that at higher velocities (over 1800 FPS), a white/greyish cloud could be seen after shooting. Don't know if it was the PC or from the gun powder. Other shooters down the line didn't like the smell of it, I never smelled a thing.

I've oven heat soaked bullets, stood up on a tray for a little over an hour at about 460*F. ESPC'd them and then put them back in the oven for 10-15 minutes to cure with the oven turned down to 400*F. Then quickly quenched in ice cold water (with ice) when taken out. Not tested but, they were super hard! I'd guess at over 25 BHN after a week.

I wouldn't try this without using my trays, 9"x11"x 5/8" thick aluminum plates with holes to fit the gas check shanks and set up with a 1" hole grid, to stand bullets up for coating. I used a bucket big enough to dump the whole tray in the water, tray and all. BTW, my tray has 35 gas check shank holes on one side and 30 cal on the other side. The other tray has 30 cal on one side and holes for 6.5 mm on the other.

The PC is supposed to have a BHN of around 26 on it's own.

 

[JonB]

I have never PC'd a bullet, but I have been given samples. So I had no control over the process, but I do have a story to offer about this.

About two years ago, I had a conversation with a person who was just starting to PC coat his bullets. He stated he was WD his COWW alloy, and hoped for 18 to 20 BHN. I told him, I thought he'd be softening his bullets when baking the PC. He didn't have a hardness tester and offered me some samples to shoot, if I'd measure the hardness of his bullets. I got some as dropped, water quenched, (but I wasn't given the water temperature), and a bunch that were PC coated (I don't recall his bake time/temp, which is why I'm calling this post a story instead of a test).

The bullets "as dropped" ranged from 15 to 17 BHN on my Lee hardness tester.
The PC'd bullets measured 11 BHN.

Both were aged about a week. I never checked them after that.

Conclusion, you "can" surely cook the hardness out of WD bullets.

 

[yodogsandman]

How were the PC bullets prepared for the indent test? Could the test surface have been "work softened" if the PC was removed?

 

[300BLK]

I have PC'ed a little, and always the shake-n-bake method. It takes a bit of practice to get evenly coated bullets, bit it is possible. My feeling is that a thin coat is better than too much. I don't have faith in PC (itself) holding rifling.

I'm sure that a 22cal bullet will be more apt to be heated through to the core in 15 minutes at 400F than a 45cal, so results are gong to vary. Too, despite having a Cabinetree hardness tester, it IS more difficult to get an accurate BHN reading on a 22cal bullet than it is on a larger one. A FN bullet is sooo much easier than a spitzer or RN.

 

[KHornet]

Agree with your summation 300BLK on the heat thru variance between a 22 cal and one
much larger. Would in my mind compare a 50 gr piece of lead to one of 200-250 or better.
To me it seems a logical conclusion.

 

[JonB]

How were the PC bullets prepared for the indent test? Could the test surface have been "work softened" if the PC was removed?

It was the Lee TL401-175SWC, no prep, I just tested the nose and the one's with PC, I left the PC intact.

 

[gman]

I found some LBT bullets that I cast awhile back. On my cabine tree they tested 19. I have them in my convection oven now. I'll heat them @ 400 for 10 minutes and I'll report back.

 

[Ian]

400 for 20 minutes is a better test from a cold start. The powder coat cure time STARTS once the piece reaches cure temperature, called "part metal temperature".