Powder coating abnomilies

twodog max

Member
Joined
Aug 28, 2015
Messages
2,165
Reaction score
4,305
Location
Arkansas Ozarks
I have been powder coating for a couple years with acceptable results. I would not class myself as an expert but by no means a total newb either.
Lately I have been observing some rather strange things with my bullets. After sizing they measure exactly as they should after passing through the sizing die. However after a period of time the bullets measure larger than originally sized and sometimes different diameters on the same bullet depending on where the micrometer happens to be. Not all my PC bullets exhibit this phenomenon. One batch for my 38/55 was so out of round they either would not chamber in my rifle of only by force. Other batches are spot on.
Is the PC elastic????
Has anyone else observed this? I suspect I my be doing something wrong in the PC process but I am not sure where the error would be.
Any valid constructive criticism would be appreciated.
 
Register to hide this ad
Since you're measuring them, how much difference are you seeing? It's never occurred to me to measure the bullets later on.

The out of round thing is really odd, especially after the fact. Are you 100% that they didn't come out of the mold that way? I have a great old mold with worn pins. If I'm not careful closing it, I get out of round bullets.

I have a dark, vague memory of reading somewhere that cast bullets can change over time. I can't pin it down. Something about letting them stand a few days before sizing? I don't know.

How about cleaning the powder coat off and measuring the bullet?

This should be interesting.
 
I am seeing differences as much as .002. No mould problems nearly new Lee mould that usually casts acceptable bullets, and after sizing if the mould was out of round the sizing die would round it up and visually I would see lopsided sizing which I do not.
I think it almost has to be powder coating problem and I will try to fix it if i can nail down what the problem is.
I have noticed that on humid days the powder seems to coat thicker before the heating process and maybe that is all it is.
 
I think I know....

I have a dark, vague memory of reading somewhere that cast bullets can change over time. I can't pin it down. Something about letting them stand a few days before sizing? I don't know.

How about cleaning the powder coat off and measuring the bullet?

This should be interesting.

Lead is so soft and pliable that inner stresses from melting and cooling that would be relieved by annealing in harder metals, relax in lead without the heating process use in annealing, or maybe the heat applied to cure the PC would do the same. Does this sound feasible?
 
Last edited:
In the section on Bullet Casting in the Lyman Loading Manual and Cast Bullet Handbook, there is a little info on alloy expansion after casting, some alloys expand a number of .0001 when cooling up to .003 on .515 bullets. As to "Going out of round" after time? I think (a WAG) that would have to do with being dumped from the mold and still semi liquid in the center.

I use an old single cavity Lyman 330 grain Postel RN bullet for my 38-55 1885 Highwall. Using the ladle method of casting, 367 out of 375 castings weighed within 1 grain, that is less than 1/3 of 1% variance. I used a certified alloy of 20:1.

Aluminum molds and pots that overheat do some unusual things to cast bullet shapes.

Ivan

ETA: like all info on the internet, some is great, and some is hooey! However, there are some very sharp guys over at castboolits.com, maybe someone there can answer you better than I can.
 
Last edited:
Coated bullets

Resize AFTER you powder coat! I wanted some heavy 9mm bullets but could not find what I wanted. I ended up buying .357" coated bullets and a Lee press thru sizing die. My fear was the process would wipe off the powder coating or damage it in some way. The end results was a .355" bullet with powder coating that was "shined up", no damage to the powder coating!
jcelect
 
Resize AFTER you powder coat! I wanted some heavy 9mm bullets but could not find what I wanted. I ended up buying .357" coated bullets and a Lee press thru sizing die. My fear was the process would wipe off the powder coating or damage it in some way. The end results was a .355" bullet with powder coating that was "shined up", no damage to the powder coating!
jcelect

I always size my bullets after powder coating them. Have never had a problem. I use the same type of sizing method as jcelect and do notice some require a bit more force to size them than other bullets. But afterwards they are the proper size and round. Yes, the coating is a bit more shiney, but still there.
 
Resize AFTER you powder coat! I wanted some heavy 9mm bullets but could not find what I wanted. I ended up buying .357" coated bullets and a Lee press thru sizing die. My fear was the process would wipe off the powder coating or damage it in some way. The end results was a .355" bullet with powder coating that was "shined up", no damage to the powder coating!
jcelect

***^THIS^***
(Or are you already doing this?)
 
Last edited:
Lead is so soft and pliable that inner stresses from melting and cooling that would be relieved by annealing in harder metals, relax in lead without the heating process use in annealing, or maybe the heat applied to cure the PC would do the same. Does this sound feasible?

Powder coat temps are applied before sizing, maybe 350F to 400F. I have never heard of lead being annealed (soften), though I believe lead will harden some from sitting.

The metallurgy of it is way above my paygrade.
 
Powder coat temps are applied before sizing, maybe 350F to 400F. I have never heard of lead being annealed (soften), though I believe lead will harden some from sitting.

The metallurgy of it is way above my paygrade.

I have a friend that quenches his bullets in water as they come out of the mold.
 
I always size after coating and they measure correct diameter after doing so. Sometimes I water quench sometimes not but water quenching is claimed to temporarily harden lead to some degree but only for a while.
I am testing these bullets now I ran the whole bad batch back through the sizer yesterday. I will now watch them for a while and see if I can measure and changes.
 
Lead can be annealed soft by heating to any temperature under 450 F and allowing it to cool slowly, but only if it was water dropped from the mold to harden it previously. An alloy of 50-50 lead linotype can not be softened to lead hardness.

Bullets can change in size after sizing especially if there are other elements in the alloy. Keeping them cold, even in a freezer was the time honored way to mitigate that, though IME they usually grow evenly, not out of round.

PC when applied properly should add no more than 0.001" to the bullet diameter. If your 38-55 bullets are more than that much out of round it isn't the PC. I would cast some out of a good alloy, PC half and leave the rest unsized. Measuring both after a few weeks will tell you more. Bullets can grow some after casting in the first two weeks but that's generally minimal.

One last thought is to check your sizing die as the problem mainly shows up on a single caliber of bullet.
 
Back
Top