Overcooked Bullets While Heat Treating ?

[yodogsandman]

Just came in from heat treating my bullets and I think I might have overcooked them.

The plan was to heat treat about a half batch (100) of NOE 360-310 FN bullets that had been sized to .360" and gas checked at 460*F or so for an hour and quickly quench them in ice water. Bullets were cast from COWW's with about 1 1/2% to 2% Sn (pewter) added. I know my temperature is off on the convection oven but, use an oven thermometer inside on the tray with the bullets to monitor the heat. In the winter the ovens temp will run 10*F over the set temperature and in summer, about 25*F over set temp. I set the temp at 450*F with a target temp of about 460*F. Didn't think that being 45*F outside isn't exactly winter temperature. So, the oven went up to 470*F and I thought it would be OK, just go back and quench them in an hour. Returned after 65 minutes and quenched them in the bucket of ice water. Swirled them around in the bottom a little with a wood stick to make sure they all cooled quickly. After a few minutes, dumped the ice water in the driveway, picked out the bullets and dried them on paper towels.

Looking at the bullets, some had what looked like scrapes on just one side of them. Just 1/8" wide and 3/4" long. Not deep, more like scratches. The bullets were discolored, too. Like they were BBQ'd. I took a couple that looked the worse and ran them in the .360" sizer again and most of the scratches came out. Now, I'm wondering if I overcooked them. I've had the discoloration before but, never any scratches. Wondering if I got so close to the slump temperature, that they scratched when I dumped them in the ice water. The bullet sides didn't show any flattening and no other signs of slumping.

I'm thinking of going back to my best load to date and trying them out. The problem there is I heat treated that batch at 430*F. So, would you guys try to just shoot them or just melt them back down and start over?

 

[Rick]

Most likely the oven was too hot. I always use a few scrap bullets in the oven for about 15 minutes before putting in the good bullets to check oven temp. 460 should get that alloy to about 25 BHN in 7 days.

As for re-melting them for me it would depend on how deep the "scratches" are, too deep and you could get gas blow by. Next would be the purpose of the bullets, plinking or match or hunting.

Just out of curiosity why do you need them that hard. In all my testing in long range revolver heat treating for high end loads much past 18 BHN starts to degrade groups. Even 454 loads were more accurate considerably under 25 BHN. I tested those at various BHN's up to 30.

 

[yodogsandman]

My best load to date with that bullet (HT'd at 430*F) was using 55.0gr IMR4831 for about 2050 FPS in my 35 Whelen. I can fit another 1.5gr IMR4831 in the case. This is just the first powder tried with this bullet. The next powder to try will be H414. So, my thoughts were that by trying a harder alloy, I might be able stretch the velocity further, while still maintaining accuracy.

This is a brand new bullet and I'm trying different powders to find "the load". Afterwards, I'll use it to take my next moose with.

 

[Rick]

430 degrees should get you to about 20 BHN, much closer to what "should" work well. I've done a huge amount of heat treat testing and the biggest lesson learned is that "hard cast" is nothing but an advertising ploy by the commercial casters, not needed. Harder is not necessarily the key to shooting faster and in my experience not for accuracy either.

See the chart at the bottom of this article.

Heat Treating Lead/Antimony/Arsenic Alloys

.

 

[Brad]

I drilled a hole in the side of my oven for a probe connected to my PID. Works like a charm! Temp hardLy varies a degree once up to temp.
I tend to HT at 425-450 for an hour. I don't care about max hardness and this works well for me. I can get my range scrap up to 20 BHn with no problems at all.

 

[yodogsandman]

Rick, I'd bet I've read that article and the chart at least a hundred times. It's "the bible" of heat treating, in my opinion. I'm still learning and experimenting.

Brad, I have all the components to put together two more PID's.....someday. Did you have to disable the oven's thermostat or just set it at max temperature and then plug it into the PID?

 

[Brad]

I set the oven to max temp and let her rip. It is so sweet to see the temp on the display just hold still.
I use one PID for heat treat and casting, it just gets moved and reset.
I'm using a 50 dollar convection oven I got at Menards on sale. Works plenty well for my needs.

 

[35 shooter]

If you were at 470 and your oven runs 10* over(480*), then yes, you were very close to slump. I wasn't paying attention and let mine get to 500* once and had several slump before i could get the temp down. They had been there about 15 min. before i caught it.

I bought a little oven thermometer to hang in my bullet oven.

 

[yodogsandman]

Found two convection ovens at a church yard sale, both for $6 each, I think. I'll have to throw another PID together this winter, I guess. This was the first time I didn't babysit the oven temps while it ran. A PID would make a fine babysitter.

 

[Rick]

I recommend the PID because your thermometer seems off. The slush (slump) temp of clip-on wheel weights with about 1% Sn is 463 and molten at 505, add more Sn and drop those temps lower.

At those temps even if not slumped they are as soft as it's possible to have them. I recommend not dumping them out on the driveway, no doubt where your "scratches" came from. See the strainer pans in the photo in the article, I lower the pan into the water carefully with the bullets standing on the bases and try not to knock them over & ding them up.

 

[GaryN]

Nice article Rick. I learn a lot on this site. I'm sure it takes a lot of time to do those tests and to compile the article. Thanks for the info.

 

[yodogsandman]

I recommend the PID because your thermometer seems off. The slush (slump) temp of clip-on wheel weights with about 1% Sn is 463 and molten at 505, add more Sn and drop those temps lower.

At those temps even if not slumped they are as soft as it's possible to have them. I recommend not dumping them out on the driveway, no doubt where your "scratches" came from. See the strainer pans in the photo in the article, I lower the pan into the water carefully with the bullets standing on the bases and try not to knock them over & ding them up.

Rick, Yup, agree that they were possibly as soft as possible, right on the verge of slump temperature. The bullets never left the bucket though, only the water was dumped out. Maybe they scratched from just sliding off the foil covered tray or being swirled around in the bucket.

35 shooter, I was using an oven thermometer. The oven can only be set in increments of 25*. I had set the temp for 450*, expecting it to run at about 460* but, it ran at 470*. The PID in the oven trick seems to be the way to go for more consistent results. That or just not try for max hardness unless I plan on babysitting the oven, monitoring and changing settings on the go, to maintain the right temps. Knowing that my oven overshoots the set temps, maybe just set it at 400* or 425* until I get a PID going.

 

[KHornet]

I did that one time with a cheap toaster oven. Melted together about 100 22 cast bullets with Gas Checks. Didn't do it a second time.

 

[freebullet]

I over cooked some powder coated boolits. It really irritated me. Life goes on.

 

[Winelover]

I use our main kitchen oven to heat treat bullets at 425 degrees. It has a "convection" mode, as well as a regular. Before using it, for the first time, I put a remote Bar-B-Q thermometer with a long probe and monitored and recorded the temperature fluctuations for a hour. Swings were never more than ten degrees in either direction. No danger in bullets slumping and they test at 17- 18 BHN after quenching. Checked and sized bullets are stood up in Altoid cans, tuna fish and or sardine cans......whatever is handy. Cans are placed in a old grilling basket, that has holes in the bottom which allows the water to flow though, as it is lowered into the ice water bath. Old towels are used for dumping and drying.

 

[Brad]

I just did 100 cast from range scrap at 440 in my PID controlled convection oven. Worked like a charm.
After 8 hours they are at 22 BHn.

 

[yodogsandman]

I HT'd yesterday, about 200 more NOE360-310 FN's @ 440*F for an hour and quenched into a bucket of water and snow. It's great not to have to make any or buy ice for heat treating!

About half way through cooking, I remembered that I hadn't sized them, yet. So afterwards got right to gas checking and sizing them. Went much smoother and faster after coating the bullets with BLL. Certainly don't want to wait more than a day to size them after....after they've started hardening up.

 

[Winelover]

About half way through cooking, I remembered that I hadn't sized them, yet. So afterwards got right to gas checking and sizing them. Went much smoother and faster after coating the bullets with BLL. Certainly don't want to wait more than a day to size them after....after they've started hardening up.

I gather you didn't size them on a Star.......ask me how I know.

 

[Rick]

Right after heat treating & quenching they are quite soft & sizing on the Star would be no problem. If there is much antimony in the alloy I sure wouldn't wait until the next day to size them on a Star or any other machine.

 

[Brad]

My range scrap, around 1.75% Sb, reaches 22 BHn in less than 12 hours after an hour at 440.
I wouldn't dream of running those thru my Star.

I have a couple ways around this. I often size before heat treat. That means I am only cleaning things up and applying lube after heat treat. Another useful tool for hard bullets is the Lee push thru type sizers. The press develops far more leverage that a sizer and is also designed to handle to kinds of forces involved. Run a lubed bullet thru every so often and it works well.