Does annealing bullets shrink them a tad?

[John#2]

I ask because I cast lead bullets for the first time last weekend.

The four-cavity Lyman mold dropped .431 from one cavity, .432 from two cavities, and .433 from the fourth cavity. Dropped these directly into water, but also measured some without the water quench.

After powder coating, they measured pretty much the same. I am having problems with this information. The coating should have made them fatter. Did the annealing during the PC heat soak shrink them a tad?

 

[AJC1]

The dropped size is a factor of lead makeup and temprature they are cast into the mould. What is your current bhn... if you are soft and your bullets are dropping heavier than the mold indicates the adding some antimony should help... I have not observed any shrinkage during PC

 

[243winxb]

431 from one cavity, .432 from two cavities, and .433

Make sure the mold is fully closed. If as cast bullets are oval, may not be fully closed? The .002" difference is not normal between cavities.

Did the annealing during the PC heat soak shrink them a tad?

Good question, that i dont know the answer too. I dont PC. I have sized bullets, oven heat treated , water cooled them to harden. No change in diameters, at any time. The bullets may not fully harden for 2 weeks if the alloy contains only 2% antimony. A higher % of antimony will speed up harding.

Alloys containing LARGE amounts of bismuth may change diameter, over time. Not something that is normally found in scrap lead or WW at high enough % to make a difference.

Sizing bullets will make them more accurate. Water dropping from the mold hurts accuracy because bullets will be different hardnesses mixed together. May not matter if the heat from PC makes them softer/annealed?

 

[Armorer 101]

You do not anneal by powder coating, you bake the coating on at 400 degrees for 20 minutes, nose down. The base up can be done with hardware cloth made into a box and a steel punch to open he holes. Then you size with case lube, using a bullet sizer die, to your gun’s grove diameter. You did slug your barrel, right?

 

[PapaG]

I ask because I cast lead bullets for the first time last weekend.

The four-cavity Lyman mold dropped .431 from one cavity, .432 from two cavities, and .433 from the fourth cavity. Dropped these directly into water, but also measured some without the water quench.

After powder coating, they measured pretty much the same. I am having problems with this information. The coating should have made them fatter. Did the annealing during the PC heat soak shrink them a tad?

you are hardening, not annealing. Annealing makes metal softer. Measure after quenching and before and after coating. You can't add a coating without increasing the dia.

 

[Archie]

When I cast bullets - a while ago - I dropped them from the molds directly into the water. I didn't do that to 'harden' the bullets (I still don't think lead has the qualities that work that way) but simply to cool them and not set the floor or table on fire. It was easier to handle the bullets sooner. No. I never measured them. If they were a trifle oversize, they'd fit the bores just fine.

Total Materia - website - says lead is "...considered normally unresponsive to heat treatment." And further "Transformations that are induced in steel by heat treatment do not occur in lead alloys, and strengthening by ordering phenomena, such as in the formation of lattice superstructures, has no practical significance."

Alloying the lead with something else will result in limited hardening, but heating and quenching is immaterial.

But it does simplify handling them. By the way, the water heats up after a bit. Not surprising.

 

[DM~]

When I use bigger molds, I fill front to back, drop the bullets, then fill back to front.

Temp of the mold/lead will make a difference in diameter, and that's how I do my best to keep the mold temp even.

DM

 

[Swampman]

When I cast bullets - a while ago - I dropped them from the molds directly into the water. I didn't do that to 'harden' the bullets (I still don't think lead has the qualities that work that way) but simply to cool them and not set the floor or table on fire. It was easier to handle the bullets sooner. No. I never measured them. If they were a trifle oversize, they'd fit the bores just fine.

Total Materia - website - says lead is "...considered normally unresponsive to heat treatment." And further "Transformations that are induced in steel by heat treatment do not occur in lead alloys, and strengthening by ordering phenomena, such as in the formation of lattice superstructures, has no practical significance."

Alloying the lead with something else will result in limited hardening, but heating and quenching is immaterial.

But it does simplify handling them. By the way, the water heats up after a bit. Not surprising.

Pure lead isn't affected by heating and quenching, but lead alloys containing antimony and arsenic (like wheelweight lead) absolutely are.

Your statement that:
"Alloying the lead with something else will result in limited hardening, but heating and quenching is immaterial"
Is incorrect and I'm surprised that anyone with actual experience casting bullets would think that.

From: Heat Treating Lead/Antimony/Arsenic Alloys
Wheel weight alloy with an average composition of: 1/2% tin, 3-4% antimony, 1/4% arsenic and 95 1/4% lead can be heat treated to well over 30 BHN

 

[John#2]

you are hardening, not annealing. Annealing makes metal softer. Measure after quenching and before and after coating. You can't add a coating without increasing the dia.

My understanding is that the heat soak from powder coating anneals the hardness obtained from the water quench. It reverses about 75% of the hardness obtained from the quench.

None of the bullet diameters increased after the powder coating. I was not expecting that result. My one time prior powder coating increased bullet diameter by about .0015”.

 

[John#2]

Pure lead isn't affected by heating and quenching, but lead alloys containing antimony and arsenic (like wheelweight lead) absolutely are.

Your statement that:
"Alloying the lead with something else will result in limited hardening, but heating and quenching is immaterial"
Is incorrect and I'm surprised that anyone with actual experience casting bullets would think that.

From: Heat Treating Lead/Antimony/Arsenic Alloys
Wheel weight alloy with an average composition of: 1/2% tin, 3-4% antimony, 1/4% arsenic and 95 1/4% lead can be heat treated to well over 30 BHN

I was using an alloy of 95% lead, 2.5% antimony, and 2.5% tin. Bars from Rotometals.

I expected the powder coating to increase bullet diameter. It didn’t.

 

[John#2]

The dropped size is a factor of lead makeup and temprature they are cast into the mould. What is your current bhn... if you are soft and your bullets are dropping heavier than the mold indicates the adding some antimony should help... I have not observed any shrinkage during PC

I have no way to measure BHN at this time.

But my issue relates to bullet size, not hardness. The powder coating did not increase bullet diameter. I was expecting bullet size to increase after powder coating. It did the last time I powder coated.

The first set of bullets that I powder coated were purchased with a BHN rating of 8, so clearly not water quenched.

 

[John#2]

You do not anneal by powder coating, you bake the coating on at 400 degrees for 20 minutes, nose down. The base up can be done with hardware cloth made into a box and a steel punch to open he holes. Then you size with case lube, using a bullet sizer die, to your gun’s grove diameter. You did slug your barrel, right?

Rifle slugs at .431, congruent with SAAMI. My Lee bullet sizer die is .430, so I can’t use it with bullets meant for the lever. I was hoping to get an increase in diameter by powder coating. Didn’t happen.

The bullets are not oval, and they shot very accurately.

Pretty sure if you powder coat after dropping the bullets from the mold into a bucket of water (water quench), you lose much of the hardness from the quench. The heat soak anneals the hardness gained from the quench.

 

[John#2]

What I’m gonna do is water quench some and air cool others, and then powder coat all to see if the diameters are the same. I know what the theory predicts. But results so far haven’t comported with theory.

 

[forrest r]

I've been powder coating bullets using the shake and bake powder coat method since 2013. The pc'd bullets have always grown in size, 2/1000th's+.

Alloy didn't matter, I've pc'd anything from plain lead to 90%/5%/5% lyman #2 alloy.

I've pc'd air cooled bullets & water dropped/cooled bullets, didn't matter both ways grew in size when pc'd.

When casting bullets for accuracy I never size the bullets down more then 3/1000th's at 1 time. If a cast rifle bullet for example cast out @ .312" in diameter that I plan on using with a finished diameter of .310":

I install a gc on them
Lube & size them to .310" with a traditional lyman 450 sizing die
Or
I install a gc on them
Run them thru a lee .310" push thru sizer
Pc them @ 400* for 20 minutes & let them air cool
Run them thru the lee .310" push thru sizer again

I understand the op is asking about bullet diameters before and after pc'ing, not bullet hardness. Figured I'd put it out there that for decades I've been heating hard alloy cores to 400 for 20 minutes+ to make them softer. Swaging dies can be on the fragile side especially the nose forming hp dies. Softening a hard core is a way to get a harder core to swage in these type dies creating a hp that can withstand impacts @ higher velocities. Typical lead cores for swaging are 6bhn/pure lead. I've heated up to 20 to 1 lead/tin alloys and used those hard cores to make jacketed hp rifle and pistol bullets. If those harder cores were not heated/annealed/softened I would of broke the nose forming dies.

 

[243winxb]

water quench some and air cool others

When i size cast bullets of different (alloys) hardness, the same .430" die may produce different finished diameters. Not Coated. Not a lot, about .0005" i think pure lead vs linotype may be very different uncoated finished diameter/results?

Is it possible to powder coat a 2nd time? This would seem to make a larger diameter finished bullet?? Just asking. Learning.

When i put a 2nd coat of paint on the house, its thicker.

 

[brewer12345]

OK, so with your alloy you are greatly hardening the bullets when you drop them in water and likely making them a bit bigger. Then you coat them in powder and bake them which softens them again and likely shrinks them just a bit. The amount of shrinkage is likely about offset by the thickness of the powder coat so it looks like you are not gaining diameter. After you powder coat, you need to do one of two things: either drop them out of the oven into water (harden and expand), or let them air cool and wait a week or two before sizing. Why do you need to wait a week or two if you air cool? Bullets grow in size a bit for a week or two if you do not water quench them, so if you immediately size air cooled, powder coated bullets you run the risk that they expand after sizing and you don't have the diameter you think you have.

FWIW, I air cool as I cast and then air cool after I powder coat. I wait a week or two and size.

 

[brewer12345]

OK, so with your alloy you are greatly hardening the bullets when you drop them in water and likely making them a bit bigger. Then you coat them in powder and bake them which softens them again and likely shrinks them just a bit. The amount of shrinkage is likely about offset by the thickness of the powder coat so it looks like you are not gaining diameter. After you powder coat, you need to do one of two things: either drop them out of the oven into water (harden and expand), or let them air cool and wait a week or two before sizing. Why do you need to wait a week or two if you air cool? Bullets grow in size a bit for a week or two if you do not water quench them, so if you immediately size air cooled, powder coated bullets you run the risk that they expand after sizing and you don't have the diameter you think you have.

FWIW, I air cool as I cast and then air cool after I powder coat. I wait a week or two and size.

 

[Thomasss]

I like brewer12345's answer. I can add to that. 1) When casting bullets, the bullets may shrink up to 24 hrs after you have cast them. 2) I drop mine onto a soft towel and allow to cool. 3) Lead alloys do not mix very well, the lead hardness does make a difference and the mold temperature can vary even from bullet to bullet sprue depending upon the type of mold you use. 4) Micrometers are more exact at measuring than calipers. 5) Powder coating thickness cannot always be measured exactly because the covering is so thin. 6) Lead powdered coated bullets are very forgiving with respect to their diameter(obturation). If the lead is completely covered, be happy.

 

[John#2]

When i size cast bullets of different (alloys) hardness, the same .430" die may produce different finished diameters. Not Coated. Not a lot, about .0005" i think pure lead vs linotype may be very different uncoated finished diameter/results?

Is it possible to powder coat a 2nd time? This would seem to make a larger diameter finished bullet?? Just asking. Learning.

When i put a 2nd coat of paint on the house, its thicker.

Yeah, I did a second PC and it helped.

But these bullets shot great, so usability isn’t the issue. It’s just weird they way they didn’t increase in diameter with the first coat of PC.

 

[John#2]

OK, so with your alloy you are greatly hardening the bullets when you drop them in water and likely making them a bit bigger. Then you coat them in powder and bake them which softens them again and likely shrinks them just a bit. The amount of shrinkage is likely about offset by the thickness of the powder coat so it looks like you are not gaining diameter.

That’s exactly what I suspected. It’s the only thing that made sense to me.

I cast again this weekend but this time was solely for the 30.06. I don’t powder coat those, so I let them air cool. I don’t want bullets too hard. This time I used Lyman’s No. 2 alloy, so the BNH should be pretty useful without a water quench.

One of the bullets is a bore riding design. Last weekend with the lesser antimony the bore riding section was .295. With the Lyman No. 2 alloy this weekend, the nose came out .300. Yeah!! One problem solved. Kind of made my day. Now I gotta load them up and see how they shoot. The .295 nose shot OK, but not what I know it can do.

 

[Blue68f100]

They had to increase it you applied it. More than likely your bullets vary in size, giving you a false reading. Or your using the cheap HF calipers which are only ±0.002" accuracy. I have a pair that if you get into the right range it's off 0.003". Check it against then std steps it's dead on.

 

[John#2]

They had to increase it you applied it. More than likely your bullets vary in size, giving you a false reading. Or your using the cheap HF calipers which are only ±0.002" accuracy. I have a pair that if you get into the right range it's off 0.003". Check it against then std steps it's dead on.

Like I said in my first post, one cavity drops then at .431, two at .432, and one at .433. Four cavity mold.

The readings are very consistent. I have a second vernier caliber. I will use that one next time also to get a second reading. So far, the dial and vernier have always agreed with each other.

None of that digital crap for me.

 

[Swampman]

John,
Did you change your powder coat process or powder type since you got an increase in diameter with your earlier powder coating attempt?

I've always gotten an increase of .0015 to .002 when I do "shake-n-bake" powder coating with Harbor Freight red. I've always thought the increase was a given, like death and taxes.

I can't explain or even understand exactly what's going on here, but the good news is that your bullets are shooting very accurately.

Is your mold brand new or did you get it used? I ask because perfectly round bullets with that kind of size variation aren't typical of Lyman. If it's used, a previous owner may have honed it out.

 

[Swampman]

Also, if you're not already alternating pours front to back and back to front as DM~ said, I suggest you try it.

 

[forrest r]

My cast bullets are 2/1000th's"+ larger in diameter are they have been pc'd.

You're using a 12bhn alloy, there is no way that that 44cal bullet is going to shrink that much due to heating them in an oven after water dropping them. A .452" bullet using 90/5/5 will only shrink .0015" if you anneal it back to dead soft.

You're only using 95/2.5/2.5 and you are not annealing the bullet back to dead soft.
You have too much tin in your alloy to affectively heat treat your bullets. This also affects how much hardening you get from water dropping them.
If you go over to the castboolits website and do a search you will see that the question "Will water dropped bullets be larger in diameter than air cooled bullets?". Multiple posts with alloys & measurements have shown a 44cal bullet will grow .0004" max when water dropped. You can get that much variance in bullet diameter from the high/low mold temps during a casting session.

With you having +/- 2/1000th's" difference in your bullet as cast you will never get any meaningful results with measuring random bullets. What you need to do is measure 10/20 bullets and size them & measure them. Out of round bullets do nothing for you. Then pc them and measure those bullets again. You'll see a huge difference in your results along with finding out how much pc (1/1000th", 2/1000th", etc) you're actually putting on.

Alloy .308 .357 .452
Linotype .002 .0025 .003
Lyman # 2 .0025 .0025 .0035
Soft Lead .0035 .004 .005