Powder Coating 101 (picture HEAVY)

[TrinityMaker]

By popular demand, I'm creating this post. Without getting too detailed as to "why" you should powder coat your slugs, I will refer you to the thread titled "Most slugs are a waste of money because you did not slug your barrel" by our friend Roachcreek, who brilliantly explained the importance of utilizing a slug that not only engages your lands, but seals the grooves of your barrel as well. You need the slug to be .0005 to .001 larger in diameter than the groove diameter of your rifle. If you're using a Lothar Walther .22 barrel, you should be using a slug with a diameter of .2215" to .222", NOT .217" or .218" (which is currently what 100% of slug manufacturers sell their slugs in). If you're shooting a Lothar Walther barrel in .25 caliber, you should be shooting a slug with a diameter of .2545" to .2550". This is because the groove diameter of the LW .25 barrel is .254", and the groove diameter of their .22 barrel is .221". There's a LOT of good info as to why you need to do this on Roachcreek's thread. So before you read through this, PLEASE (for your own good and piece of mind) read all of the posts on that thread. 

Well, since 100% of slug manufacturers mass produce slugs smaller than the groove diameter of every .22 barrel manufacturer and almost every .25 barrel manufacturer, what do you do to compensate for the concentric gap that is present around the circumference of the slug when it's seated in the breech/barrel? The gap that allows for the slug to cant, which induces wobble and instability, and the gap that ALSO allows for high pressure air to escape around the slug before the slug ever even exits the barrel- which ALSO results in instability and wasted energy? The answer is you powder coat your slugs. If done properly, you can build up a concentric and even level of material to compensate for the gapping, and create a slug that seals against the grooves in your barrel. So it is my intention to educate you guys on this process. This thread will be VERY picture heavy. 

Disclaimer..... I am by no means an expert on powder coating. I've been doing it for about 6 months now, and through a lot of trial and error I have come up with a process that works well for me. So it's safe to say that if you follow my advice, you can achieve similar results. Also, since no slug manufacturers (with the exception of Stephen from AVS slugs who makes a proper .254" slug for .25 caliber) currently make slugs that actually properly seal in your .22 or .25 barrels, you will need to bite the proverbial bullet and take the time to do it properly. This is NOT a fast process. But if done right, they results will be BEAUTIFUL, evenly coated, concentric slugs that seal your barrel, and prevent leading. So here goes:

The following are picture of the materials you will need for this process:

1. Small Toaster Oven (able to get to 400 degrees F)

2. Silicon Baking Mat (cut to fit baking sheet from toaster oven)

3. Digital Caliper (Harbor Freight is fine)

4. Harbor Freight Vibratory Tumbler

5. Good Powder Coat (Eastwood or Powderbuythepound.com)

6. Acetone ($6 from Home Depot)

So the first thing you're going to want to do is to clean the manufacturing lubricants off of your slugs. Powder coating powder HATES oil. So the slugs need to be really clean. That's what the acetone is for. Pour some acetone into a plastic container with a lid and add your slugs. Let them sit in the acetone for about 10 minutes. Swirl them gently, but not aggressively. You don't want to run the risk of damaging the small details of the slug, like the hollow point or the edges at the rear. It's not necessary to shake the crap out of them to remove the oil. The acetone will take care of business! 

Once the slugs have soaked, pour them through a strainer and save the acetone. You can use it over, and over again. Dump them onto a paper towel to dry. Make sure all of the acetone evaporates off of them. If there's any acetone on the slugs, and you put them into the powder, the acetone will melt the powder into a goopy mess. They MUST be dry. DO NOT touch your slugs. Use nylon gloves when handling throughout the entire process. 

Also, get yourself a good pair of needle nose (medical tweezers). This is what you will use to handle the slugs once the process of coating begins. 

Now lets start coating!

Pour a few heaping tablespoons of the powder into the tumbler. Less is more. You DO NOT need to dump the whole container. The powder WILL stick. The reason the powder sticks is the whole process of the slugs tumbling and rubbing against the plastic bowl create an electrostatic charge. Like when you rub your shoes on the carpet and zap someone. The powder takes on a charge, and the slugs take on an opposing charge. The oppositional charges are attracted to each other. So the powder will evenly and concentrically stick to the slugs. The more slugs you coat at once, the stronger the electrostatic charge, and the faster they will coat. But the coating will only get so thick. Don' think that if you leave the slugs in for an hour, you can get away with one thick coat instead of 4 or 5 thin coats. It's just not going to happen. Just enjoy the process, and come to terms with the fact that it's going to be a bit time consuming. But the reward will FAR outweigh the sacrifice. 

Here are the slugs I will be using for the coating process. As you can see, they are exactly .218" in diameter. They are 28.5gr NSA in .22 caliber and 30gr from Griffin slugs in .22 caliber. I coated 12 of each slug. 

Here's the tumbler with 3 heaping tablespoons of powder in it. 

I recommend you warm up your slugs first. Get them up to 140-150 degrees. The powder sticks better when the slugs are warm. Don't get them too hot though, or the powder will clump. 140-150 degrees is perfect. Then dump them into the powder, screw down the lid TIGHT, and turn on the tumbler. Let it run for 10 minutes. In the meantime, get your toaster oven up to 400 degrees. After the slugs have tumbled for 10 minutes, turn off the tumbler and remove the lid. You will see some beautifully, concentrically coated slugs. The coating will be thin. Don't worry about it. You're going to repeat this process 4 or 5 times. 

Take your tweezers and 1 by 1 remove the slugs. If they have a hollow point, squeeze the slug with the tweezers flip the slug upside down, and while gripping the slug tap the tweezers once ot twice on the rim of the tumbler (dumping the very small amount of powder in the hollow point back into the tumbler). Carefully place each slug base down onto the silicon mat that's lining the baking sheet. Make sure you have it set on a very flat surface. 

Now some of the YouTube videos that guys make who coat bullets talk about pouring the slugs onto a mesh aluminum screen and shaking the powder off of them. I don't recommend this with small caliber slugs. The slugs there guys are coating are 175+ grain, and they are coating 300-400 at a time. So the surface area of the slugs in conjunction with the electrostatic charge of the tumbling process not only allows the powder to stick better, but it creates a thicker coat. You're not going to get this with the smaller caliber slugs. You will get better adhesion with larger batches, but not like the adhesion you'd get with a large batch of large slugs.

Also, they will water quench their slug when they pull them out of the toaster oven. Don't do this. That hardens the lead. Just let them slowly air cool.

The powder takes 20 minutes at 400 degrees to fully cure. HOWEVER, you will NOT be fully curing it yet. It is possible to over cure the powder, and it will change color and become brittle. You want it rigid, yet malleable to conform to the inside of the barrel. So instead of going 20 minuets, you will go 5 minutes. Just long enough to get the powder to form a cohesive shell. After 5 minutes, pull the slugs, and let them cool down to 150 degrees. If you have a laser thermometer, it will be of great benefit to you as you can aim it at a slug and tell precisely when the slug has cooled to 150 degrees. When they reach 150 degrees, dump them back into to powder for round 2 of coating. I want to reiterate, DO NOT touch the slugs with your bare hands! Use the gloves. You don't want to deposit your body oils onto the slugs and contaminate the process. The powder will not stick if there are even trace amounts of oils present. 

You are going to repeat this process 4 or 5 times. If you do it 4 times, you will add approximately .0015" of concentric girth to your slugs. That means .003" of increase in diameter. I suggest 4 coats minimum. The following are pictures of the 4 coats I added step by step. Notice how each coat reveals less and less of the lead showing from the slug. 

Coating #1 (First pic are slugs when pulled from the tumbler. Second pic, slugs cured for 5 minutes at 400 degrees)

Here's layer 2. Same process as Layer 1.

Here's layer 3

And finally Layer 4. The last layer will go for the FULL 20 MINUTE CURE TIME! In this final baking step, you are fully curing all 4 layers into 1 layer. Here's the 4th layer before the cure, and after the cure. Notice how BEAUTIFUL and shiny, and evenly coated the slugs are.

Now it's time to see if all our work paid off. I left the caliper at the original diameter of the slug- .218". Let's see if they still fit in the gap of the caliper.

The answer is, NOPE! They're definitely bigger. But how much bigger?

Looks like we added .0015" of concentric thickness to the slugs, for an overall increase in diameter of .003" My barrel is a custom .22 made by my buddy Alex in Russia. It has a groove diameter of .220 and a twist of 1:16. 

Here's a shot of the empty barrel mounted on my Air Force platform.

Here's me slugging the barrel with one of the Griffin 30 gr .22 slugs in .218" diameter. I didn't slug the .22 NSA slugs because for some reason Nick added antimony to this batch of slugs, and they were very difficult to push through the barrel with a cleaning rod. 

Which brings up another issue.... There's no need to EVER add antimony to slugs used in air rifles. You want your slugs to be pure lead. The only reason you would increase the BHN (hardness) would be to prevent leading and deformation associated with superheated gasses from powder burners. It's not necessary for air rifle slugs! PERIOD! But Nicks ammo had antimony added, so I only slugged the Griffin slugs. 

After seating the slug in the breech, I went to the muzzle end to stare down the barrel. Notice the LED flashlight I have shining behind the slug. 

So when you guys see this next picture, you're going to automatically think that I mixed up the pictures, and that the flashlight is shining down an empty barrel. You are wrong. The following picture is with the slug in the lead of the breech. Most barrel manufacturers "soften" the lead, and remove some of the aggressiveness of the rifling. That way you can partially insert the slug into the barrel before the rifling concentrically engages the slug and "grabs" it. So there's going to be more light present at the breach than anywhere else in the barrel during the slugging process. 

Here's the slug pushed 12" into the barrel. Notice the nice little star pattern of light. The lands are fully engaged, but the grooves are NOT sealed.

Here's the slug pushed to the end of the barrel. The larges portion of the diameter of the slug still fully engaged in the rifling. Notice how much light can be seen from the grooves around the slug.

And here's the slug after being pushed all the way through. Notice the nice engagement of the lands, but ZERO rubbing or deformation in between the engagement points where the grooves would/should seal.

Now lets repeat this with the powder coated slug.

Here's the slug seated in the breech. Remember, the rifling in the breech is VERY loose, so there may be trace amounts of gapping and light present. But as the slug is pushed through the barrel, it will completely and totally seal, and there will be zero light in the grooves.

Powder coated slug in breech:

The next pics display the dept of the slug in the barrel. I'm estimating 14-16 inches. You can tell the depth by the cleaning rod I'm using to slug it. It is touching the back of the slug in the barrel. 

Here's looking at the front of the barrel with the powder coated slug 1/2 way inside. Notice ZERO light can bee seen from the grooves.

Here's the slug pushed to the muzzle, just like the un-coated slug. Again, ZERO light. This means proper seal of the slug throughout the length of the barrel

Here are the two slugs (after slugging) side by side

And that's it guys! That's how you add concentric mass to your undersized slugs to increase efficiency and accuracy, and eliminate lead fouling inside of the barrel. 

This last picture is to prove the durability of the powder coating. It's the "smash test". You take one of your powder coated slugs and smash it on the ground (nose side up) with a hammer. The little dimple near the center is the bottom of the hollow point:

This is the smashed slug turned sideways. Notice the mark from the rifling is still present. But most importantly, notice the ZERO of the powder coat rubbed or chipped off, even after smashing with a hammer. If it doesn't rub off with a hammer strike, it's not going to rub or flake off in your barrel

If you guys have any questions whatsoever.... I'm an open book. I want you guys to be the best marksman you can be! 

Thanks for reading. I hope you enjoyed.

 

[Guest]

Please pardon my own ignorance but it appears the emissitivity of both rounds appear the same (relating to frictional coefficient) and the grooved rifling on both projectiles are equal. It appears that the powder coated round has more rifling engagement towards the nose which suggests out of round and energy expense resulting mass centering and spin stabilization? Based on the images shared and rifling engagement it seems the uncoated projectile is superior?

Thank you in advance!

 

[MScottLeeman]

I would avoid putting acetone in anything plastic!

Other than That, Thank You for your work,

Mike

 

[Loren]

Good Job!

A tip for laoding them standing up on your baking sheet/pan.

Also use nitrile gloves, with fingers dipped in the powder to handle vs using tweezers.

I use 9mm pistol ammo trays. Load in trays and then with baking pan vertical to sligthly upside down I hold the trays in the pan and then flip it over.

 

[Corvid_hunter]

Very interesting. Thanks for the post.

 

[TrinityMaker]

This is the container I use to soak my slugs. It's plastic. It was designed to hold acetone as the Walgreens label indicates. Maybe I should have said, clean them in a chemical resistant plastic container. 

 

[TrinityMaker]

I'm not sure why the term emissivity was used as all I've read on it pertains to thermal applications. 

If your reference to frictional coefficient was in response to my implication that the powder coat increases lubricity, then that would be an accurate application. NSA started lubricating their slugs before shipping now because lubricated slugs decrease lead fouling and friction. That's what lubricants do. That's what the powder coat does. Its like a malleable Teflon coating. You'd have to hold it in your hand and squeeze it between your fingers to understand. But it also increases concentric mass, which dry film or silicon lubricants do not. 

Since the diameter of the slug increased by .003", then the rifling engagement will be slightly deeper, and the marks will appear longer on the slug, encroaching higher towards the nose since the rifling engagement on the non coated slug stopped at the curve towards the nose. It's simple physics. That being said, There's no indication whatsoever from the picture of the slugs that the coated slug sat canted inside the barrel. 

I'm wondering if you had an opportunity to read the other thread I referenced at the beginning of this thread? Then you would have a solid understanding of why I posted this in the first place. 

Perhaps you could tell me what other images I shared indicate the non coated projectile is superior, since your whole concern revolved around the 1 picture of the 2 slugs that displayed the marks from the rifling engagement. 

These questions are not to challenge your character or intellect. I just don't think there's a more refined way to ask them. 

 

[Vetmx]

Thank you. Nice job.

 

[jwrabbit123]

HI wow you sure put alot of time in this , great information , However , I have to disagree , I have been using lead slugs for decades .

First not all slugs should be pure lead , low power slugs yes but the bigger hunting slugs need to be harder for a few reasons

1.penatration

2.they shoot better long range

3.better presentation

4. they dont get damaged during packaging ,

I use and all major airgun slug companies , (not backyard casters ) use 95% lead 5% or close ,



Next powder coating

While I see you are correct with filling voids ,

The real problem is the coating is too hard ,

Alot of slug manufactures have tried it and when it ate up sizing dies prematurely it was dropped ,

also the sizing dies are much harder then airgun barrel ,

You need to research this ,

Barrels will be worn out very fast and with lead they never wear .



LOU

 

[Loren]

Lou, can you provide some reference data to support your claims?

Such as how hard should a lead bullet be for an airgun?

How does a harder projectile shoot better at long range?

How hard is the typical powder coat? Is it harder than 95/5 lead alloy?

How many barrels have you seen worn out from powder coat use? How did you know it was worn out?

 

[TrinityMaker]

Lou,

I disagree with several things you said. First of all, the powder coat (if cured properly) is smooth and malleable (soft/pliable). It encases the slug and becomes a singular cohesive film/shell. 

If the coated slug ruins dies, it's because they are doing the process wrong. All of the online channels dedicated to powder coating will tell you to resize the slug prior to coating it. Then after you coat it, resize it again. Then you're only stepping it down by .0005" to .001" increments. 

Also, these guys all water quench their slugs when they're done curing. They take lead that is already blended with antimony and tin to increase hardness and they rapidly cool them from 400 degrees to 50 or 60 degrees by dunking them into a bucket of water. This makes hard lead even harder. Remember, the reason they increase the hardness of their lead is to prevent lead fouling in their barrels. Superheated gasses plus 50,000 psi to achieve supersonic speeds is a recipe for leading in the barrel. That's why they powder coat. The pressure used to push the hard lead down the barrel of the powder burner is 15-20 X's the pressure your valve and tank use to propel your slug downrange. 

Loren's questions are very valid. If you're shooting big bore rifles, your slugs are more than likely cast, not swagged. The smaller the projectile, the more susceptible it is to negative performance effects of small deformations from shipping. But not so with big bore ammo. The larger surface area lends it to be less susceptible to negative aerodynamics and performance from small deformations on the nose, sides, or rear of the slug. 

Most of the big bore shooters I know cast their own slugs. And their goal isn't bench rest accuracy. It's hitting a "kill zone" on a target. MOA shot placement takes a back seat to penetration and energy. Close is good enough when your target is a 6" x 6" heart/lung shot. 

But I can personally tell you that the powder coat absolutely, positively is NOT hard. The only time it would become hard would be if it was over cured (in which case it would just crack and crumble off when you pushed it into the breech). If there was increased hardness, it comes from the alloy blend or rapid quenching. That's why I specifically said to let the slugs air cool after the final cure. They take about 4 minutes to cool, thus you're not tempering them. 

 

[nomojo65]

Deleted 

 

[TrinityMaker]

Here are pictures of the 2 slugs. You are correct that different ogives will yield different results regarding engagement. 

The only reason I didn't slug the barrel with the NSA slugs is because for some reason Nick at NSA used an alloy blend for his lead wire instead of pure lead. So although I could get the slugs to engage the lands from the lead, I didn't feel comfortable pushing them through the length of the barrel. I didn't want to run the risk of applying so much force that once the rifling fully engaged, and the slug started to move, I would have enough force and momentum behind the rod that IF for some reason it canted in the barrel, it could damage the rifling. So I conceded to just slugging the 30gr slugs with the 2s ogive. To be honest, I believe the NSA slug with the larger hollow point and less aggressive ogive would have better engagement. 

But I assure you that all the slugs I held, pictured, and pushed through my barrel were the same. 

 

[Vetmx]

TrinityMaker, your topic is called Powdercoating 101. You spent enough time and effort telling guys how to powder coat slugs. Don’t waist your time trying to debate it. That’s for another topic. There is no need to sell it to skeptics.

 

[Loren]

Amen!!

 

[Guest]

I'm not sure why the term emissivity was used as all I've read on it pertains to thermal applications. 

If your reference to frictional coefficient was in response to my implication that the powder coat increases lubricity, then that would be an accurate application. NSA started lubricating their slugs before shipping now because lubricated slugs decrease lead fouling and friction. That's what lubricants do. That's what the powder coat does. Its like a malleable Teflon coating. You'd have to hold it in your hand and squeeze it between your fingers to understand. But it also increases concentric mass, which dry film or silicon lubricants do not. 

Since the diameter of the slug increased by .003", then the rifling engagement will be slightly deeper, and the marks will appear longer on the slug, encroaching higher towards the nose since the rifling engagement on the non coated slug stopped at the curve towards the nose. It's simple physics. That being said, There's no indication whatsoever from the picture of the slugs that the coated slug sat canted inside the barrel. 

I'm wondering if you had an opportunity to read the other thread I referenced at the beginning of this thread? Then you would have a solid understanding of why I posted this in the first place. 

Perhaps you could tell me what other images I shared indicate the non coated projectile is superior, since your whole concern revolved around the 1 picture of the 2 slugs that displayed the marks from the rifling engagement. 

These questions are not to challenge your character or intellect. I just don't think there's a more refined way to ask them.

No offense taken at all and thank you for taking none to my initial ask as well. I've been reading down and I see that you've answered many of my own ignorant questions with more data. Thank you for taking the time to make this post, respond to my question with an exceptional explanation, and answer additional questions with more information. Nicely done and appreciated!

 

[TrinityMaker]

TrinityMaker, your topic is called Powdercoating 101. You spent enough time and effort telling guys how to powder coat slugs. Don’t waist your time trying to debate it. That’s for another topic. There is no need to sell it to skeptics.

You're right. Thank you for reminding me. 

 

[Long_Shot]

 Great post you've done. I like to try new things. So this caught my attention, when you mentioned doing it back in the other slug bore size post. 

My only concern would be the tumbler step. For a small delicate HP .25 cal. I might need a "dimmer" to lower the vibrating speed on mine. If I had powder here I could toss a few slugs in and find out if it damages them. I might need a slow speed and an introduced static charge to the plastic tumbler bowl to get the powder to stick without damaging them. 

TrinityMaker, your topic is called Powdercoating 101. You spent enough time and effort telling guys how to powder coat slugs. Don’t waist your time trying to debate it. That’s for another topic. There is no need to sell it to skeptics.

Well put. Keep it a how to. 

A different post about the very strange property's of some "soft" plastics ability to destroy Carbide or any hardened steel very fast, is it's own topic for sure. 

 

[TrinityMaker]

Don't worry about damaging your slugs from the vibratory tumbler. The only time the tumbler damages anything is if it's filled with abrasive media to remove rust or to polish rough edges. I've run my slugs for an hour straight with zero damage. One of the slugs that I powder coated on the thread was a 30gr slug in .218 from Griffin slugs. They are made from pure lead wire, and they are very soft an malleable. As you can see, there was zero damage to the fine details of the nose or the base. I think this is due in part to the process I use. Remember, you're adding multiple concentric layers. You're only tumbling the slugs for 10 minute intervals. And once the first layer of powder has been applied and semi-cured, you have a great layer of protection for the additional layers and tumbler runs. Every layer you add gives you more protection from any potential adverse effects from tumbling. So at most, the longest they tumble in their virgin form is 10 minutes. After that, you're home free. 

But like I said, in my R&D from tumbling slugs, I've run small detailed slugs for almost an hour without any deformations or negative side effects. This is just a 10 minute run, then you're set and you can be confident the additional runs will have zero negative impact. 

Loren uses loading trays to expedite the process. I think that's a BRILLIANT idea. I may buy some, or make my own from polycarbonate or acrylic sheets. That's WAY FASTER than loading them onto the tray 1 by 1 with tweezers. Thanks for that suggestion Loren. I shall adopt it for future coating jobs! 

 

[Vetmx]

I just did a batch of .250 slugs. After 4 coats they came out .258. Used Harbor Freight powder so we know where that stuff came from. My guess is the type/quality of powder will have an effect on how many times you coat them to achieve what you are looking for. Waiting on better powder before I proceed. Next time I will check the slugs diameter between coats.