Powder coat problem.

[STIHL]

Guys I have been doing this for a while and I have only had 1 batch that the powder would flake off of. The other night I did some 458-193 405 in the same powder I had the trouble with the last time and it flakes off. Well powder is contaminated, or so I thought. Trash that batch of powder and continue on with another bowl I haven’t had issue with. Just to make sure, I ran a test batch of 10 in some different powder they came out great, so I went on about my business and did about 50 last night along with some 429-421 and some 30 cal too. I start sizing them today and several of the 458 the powder flakes off when they go through the sizer. I test some of the 429s no issue at all.

My question is has anyone had this happen? Am I not baking the large boolits long enough? I’m at 400* for 20 minutes that’s from time they go in the preheated oven until the timer quits. Or have I got some contamination in my buckets I put my boolits in to season. The only difference in any of these boolits are what the went in after casting

Im definitely going to wash the next batches out of my bowls that I thought were clean in acetone and for future endeavors I will have dedicated bowls to put my fresh cast boolits in to avoid any cross contamination. The flaking is minimal and I’m going to load them, I may live to regret this decision, but I’ll never know what I can get away with until I try.

I may have just answered my own question but what say you guys.

 

[Joshua]

Cure time starts when the bullet has hit “part temp” of 400°F. You will see the powder liquify, that happens at a lower temp than 400°F, I guess it liquifies at around 325°F. I wait five minutes after it liquifies and then start my 20 minute timer. I end up with a 30 minute overall cook time.

 

[Ian]

Exactly, Joshua.

However, my experience with under-cured bullets was that the coating got softened by the propellant powder and left plastic streaks in the bore that were just about as close to impossible to remove as could be, never have I had powder not stick to the bullet. I have no idea why it wouldn't unless you're pre-sizing with some sort of lubricant that leaves a residue.

 

[CWLONGSHOT]

My first reaction was contaminant. Not under cured. But of coarse it's a reaction not a fact.
I do not even touch bullets I powder coat. I rarely quench, IF I do, its clean cold water with ice. Changed regularly. Clean cotton towels and bullets COMPLETELY and Absolutely dried in a basket, on top of the preheated oven.

Josh is right a d its something many miss. Its 20 min AFTER POWDER FLOW @ 400 degrees. Luckily and in my experience a bit longer does not hurt.
Second thing, is something you brought up. The more you load in the larger the mass to heat to temp so longer the time to bake.

Good luck

CW

 

[Brad]

I would suspect something on the bullets preventing proper adhesion.

As for bake time I go with 30 min for smaller bullets and 35 min for anything 240 gr and up. I don’t cast many long, skinny rifle bullets so my heavies are short and fat and I want plenty of time to let the bullet get to temp so the powder flows well.

Most of the powders can handle a long or over temp baking just fine.

 

[Ian]

I've gone up to 430⁰F for 50 minutes (what it takes to loosen up the atoms for a good quench hardening) and even quenching straight into cool water never had trouble with the powder. Presizing so bullets are slick, frosting bullets, no matter, it sticks so well you can't get it off without scraping some lead away with it. The polyester powder with the TGIC cross-linker is VERY forgiving stuff. Someone was doing experiments with different pre-sizing lubes to see about not having to wash before coating and as I recall one of the cable-pulling gels worked very well if just a film was used for sizing, no washing necessary.

The only bullets I've had trouble coating via shake/bake have been ones in the 18+bhn range.

 

[fiver]

I HOLD my bullets in the flow stage for a full 20 minutes, then I kick the temp up to cure temp and set the timer for 20 minutes when it gets there.

IMO if your PC is merely flaking off in spots after cooking something is on the surface preventing the coat from sticking.
it doesn't have to be an oil either junked up alloy with carbon inclusions or over tinned alloy can do it too.

 

[358156 hp]

STIHL, how are you handling the bullets? Are you using tweezers, wearing gloves, or something else? My procedure closely mirrors Brads. I bake for 20-25 minutes after the powders reach the flow stage. My PID is set for 430*.

 

[STIHL]

Ok, you guys have opened up a few holes in my powder coat game that I didn’t even think about until now.

the ones I’m having flaking. The powder is cured, I actually baked them 35 minutes because I forgot to set the timer. So that tells me I’m having flaking due to contamination, most likely from my fingertips, I’ve never thought about sorting them with my bare hands, duh. After I apply the powder I use tweezers or glove to put them on the baking tray. I also wash the bins I put them in after casting. There may be some soap residue in them. Everything I PC from this point forward will be washed in acetone and I will not touch a. Upper without a glove on if it’s to be powder coated. I had figured it was contamination after I typed the post, because the ones I coated with the problem bullets were from the pot to the metal tray then to the powder coat with gloves on. I’ve gotten lucky in the past to have not had issues until now.
Future reference I’ll make sure the powder is flowing then start my timer and I’ll take better care as to not get contaminates in the bullets this should solve my issue of having this problem again.

 

[Brad]

I touch mine with bare hands many times before coating but I will admit I make sure my hands are clean before doing so.

 

[CWLONGSHOT]

Stihl, I have a number of videos on my process. I dont make any claims it is the only way but it works for me a d I do PC quite a bit. Maybe it can help you.

CW

 

[popper]

I've had trouble with high BHN bullets scraping PC of in the Lee sizer. Found some crud scraped off and every one after that scraped. Sometimes I'll use H2O or tumble in BLL (after PC cook), basically lubes, cleans the sizer. Some clean with acetone to eliminate the contamination. One OP had weird contamination in the alloy and had to acid wash to get the PC to stick.
I have more trouble with flaking HiTek than PC.
I cook on a hot plate, Yoshi copper cooking sheet lasts much longer then foil. I ground off the bottom of 45acp plastic holder, just tap excess powder off, drop in hole and they are aligned. Get 50 'loaded', pull holder off and repeat. No moving, cook and the dump in cold water to H.T. (rifle).

 

[STIHL]

I have never had a problem until now with touching them. Which really leads me too contaminants in the bowl I stored them in. Going forward though I will try not touching them at all and see if it improves my coatings. I wash my hands 100 times when messing with lead. But either way. Never hurts to try something new.

 

[STIHL]

The larger bullets do fit the sizer pretty tightly so I use hornady one shot in the bullets to give them a little extra slide. I haven’t hand issue with 44 bullets, but some 357 w gas checks have been pretty tight too. And I have had no issues with them, so it has to be contamination in the bowl. Plus the alloy for my 45-70 is the same as I have cast those 44s out of and 357 it’s just straight COWW which actually needs about 2% tin added having some fill out issues at times.

contaminants in the bowl has to be the culprit. No problem. I’ll acetone wash them and try again and see what happens. Also going to acetone wash the rest I have stored up in these containers. I have some stored in old powder bottle and glass jars that should be fine, but if they have been in a metal or plastic tub I’ll wash them and put them in clean new containers. Like a Rubbermaid bowl or a ziplock bowl. That should do great for storage and keeping dust out, or any other contamination.

 

[STIHL]

@CWLONGSHOT very nice video, it’s nice to see how someone else does it first hand. I like the basket trick. Those are much nicer than my homemade rigs out of hardware cloth.

 

[Ian]

I like to pre-size bullets when they're going to come out more than .002" larger than I want after coating. I usually size them dry, but if they give me problems I roll them on a case lube pad and wash them in acetone afterwards.

An example, the MP 311-180 silhouette drops at about .3115" with my alloy. I seat the gas checks and partially crimp them with the Lyman 45 and check seater stop from a 450. Then I push them through a Lee .309" sizer. Then they get coated and air cooled, then right away, before they start to precipitation harden, I nose-first size in a two diameter die to clean the nose and size the body back to .3095" in concentric fashion.

For .458 Socom I shoot the Lee 457-500FNGC without the check. They cast about .459" and I knock them back to .458" and then coat, then size the noses to .452" and the body in a .458" die so they come out about .4585" which is perfect. If I try to do all the sizing after coating, they spring back to .458" and won't chamber. I suppose I could get a smaller die, but it's too much to size from .461 to .458+.

 

[STIHL]

I’ve been getting away with .003 or so on sizing. On those 457-193 down to 458. Been using a die in the SAECO I haven’t looked for a 458 Lee push though. But if I keep foooong with these 45-70 PC then I’ll get me a push through.

 

[Brad]

.003 is a bit of sizing.

I would try sizing first, coating, the sizing again.

 

[fiver]

especially if your die doesn't have much taper to it.

 

[Brad]

Sizers with a gentle lead in taper are to die for