Does black powder always clump in your mill?

December 26, 2024

I've been making my own BP for a few years. Mostly for pyro, and 4-6 hours in a mill seems good enough for stars, lift, etc.

If I go any longer all the powder starts sticking to the sides of the jars. (Sometimes sooner) I read somewhere folks saying that just means it's done.

I've tried larger jars, more media, less media, switching from hardened lead to various sized brass balls and shapes without any better results.

I recently got into muzzle loaders and I'm trying to emulate some of these folks and their powders. One guy in particular mills some of his for 48 hours or more.

I can't understand how it can be done. I bake my KNo3 for a number of hours to make sure it's dry, my charcoal comes straight from the retort to the grinder, to the jar. But no matter what I do or try, after a short period the powder clumps and I have to knock it off the sides, or rescreen it constantly.

I'm fully aware that there are other methods for making BP, but I'm just wondering if this is just the nature of the beast for eternity, or is it just me?

Thanks.

December 26, 2024

If you dry your KNO3, then I wouldn't be surprised if you still have some moisture in your charcoal, it seems to have a magic ability to gain and retain moisture.

I am of the opinion that smooth surfaced, short & long mill jars (with or without lifters) seems to make the clumping issue worse. I could speculate, but it would be a pure guess. Are you using a homemade mill jar, if so what kind?

For clumping in the mill jar, I used to typically get clumping after a few hours, especially in the summer, but sometumes in winter when its colder (even when I dry the KNO3 and Charcoal) when using a short but long ball mill jars (PVC / sponenburg type). Now I use the rebel mill jars, and rarely have clumping as an issue from milling for 2.5-3 hrs. After 2.5-3 hrs, that's been the "point of diminishing returns" for B.P. strength for me (I don't see much improvement after that, nor do I need anything stronger).

I also noticed that when the KNO3 was already talcum fine, and the charcoal was not, that I would get clumping. Again, no science there, just observation - now I mill both together instead of keeping individually milled components on hand.

Comparing what we call B.P. (where decent power and good consistency is most important) to theirs (where max fps based on the most they can pack in a small /given space) is an "apples to oranges" comparison in my uneducated opinion. The B.P. folks I've seen that prove their B.P. by shooting muzzleloader and measuring maximum fps achieved process it differently tgan most pyros do. They said they aren't using an optimized mill with the correct amount of media (correct as we in Pyro community believe it to be), in fact the T.P. B.P. guy (I think) showed an unmodified rebel ball mill that turns at 36-40 RPMs, far below the 69-75 that is used by pyros. They also press and corn tgeir B.P. to a specific density for both density and sometimes volumetric measurements. Point is they process it differently and receive different results.

If you're powder is good for your purposes, why mess with a good thing.

December 26, 2024

After rereading your clumping issue, I've never had it stick to the sides of the container. Mine has been mostly at the ends or a big solid clump of B.P. and occassionally milling media just rolling around.

What kind of media are you using?

December 27, 2024

To reiterate, I don't have much problem running a 4 or so hour pyro batch, using either my harbor freight small rubber jars, or my large homemade 10" tall 15" long HDPE jar with lifters.

It's when I go beyond 4 hours or so that the sticking starts.

As I previous wrote, I take my charcaol straight from the retort once cooled, run it through the blender, and straight in the the mill jars. There's no time for moisture to infiltrate. Besides that, I live in the AZ desert. Very little humidity.

I've used hardened lead, as well as brass.

As far as pyro powder goes, mine is just fine, but at this point I AM after the faster FPS for muzzle loading, and I've seen it proven over and over that longer milling times do make a difference. And as for my shooting powder, I do the whole press and corning thing under a 20 ton press.

I've also experimented with different carbon sources from cottonwood, to bamboo, to TP, to hemp and so on, and believe me they do all contribute to differences in behavior and cleanliness in their burn. I've also experimented some with ratios, but haven't proven a difference to myself yet.

It's just the clumping that's driving me nuts. Once it starts, it can only be broken up or screened and packs up again within minutes.

Thank you for your thoughts and reply.

December 27, 2024

My guess was either the jar or media needing drying, but it sounds like your location should eliminate that as a problem.

December 28, 2024

21 hours ago, Giuseppe said:

To reiterate, I don't have much problem running a 4 or so hour pyro batch, using either my harbor freight small rubber jars, or my large homemade 10" tall 15" long HDPE jar with lifters.

It's when I go beyond 4 hours or so that the sticking starts.

As I previous wrote, I take my charcaol straight from the retort once cooled, run it through the blender, and straight in the the mill jars. There's no time for moisture to infiltrate. Besides that, I live in the AZ desert. Very little humidity.

I've used hardened lead, as well as brass.

As far as pyro powder goes, mine is just fine, but at this point I AM after the faster FPS for muzzle loading, and I've seen it proven over and over that longer milling times do make a difference. And as for my shooting powder, I do the whole press and corning thing under a 20 ton press.

I've also experimented with different carbon sources from cottonwood, to bamboo, to TP, to hemp and so on, and believe me they do all contribute to differences in behavior and cleanliness in their burn. I've also experimented some with ratios, but haven't proven a difference to myself yet.

It's just the clumping that's driving me nuts. Once it starts, it can only be broken up or screened and packs up again within minutes.

Thank you for your thoughts and reply.

Then good luck to you, maybe you should ask the guy that mills it for 48 hours 😉.

Edited December 28, 2024 by cmjlab

December 28, 2024

4 hours ago, cmjlab said:

Then good luck to you, maybe you should ask the guy that mills it for 48 hours 😉.

I have, twice even. No reply. But I suspect I'll get one eventually, or maybe he'll take the time to make a video on the whole thing.

Many in the pyro industry say there's nothing to be gained after it reaches the caking and clumping point after a few hours with a decent mill, and I agree, but the velocities, or FPS that can be gained in muzzleloaders with extra mill time is hard to argue with.

In pyro, fast is good, sometimes, too fast might not be what the Doctor ordered.

On top of it all, being a noob in the realm of flintlocks, I'm enjoying the learning, the experimentation and the ride.

Maybe I'll even post a few videos once I get some things dialed in.

Edited December 28, 2024 by Giuseppe

January 1

Are you baking your C & KNO3 in a gas or electric oven?

Electric ovens are 'almost' foolproof. But benefit from occasional opening to remove vaporized water.

If using a gas stove, you need to vent the natural water product of combustion more frequently, or it will just get immediately reabsorbed by your chems. Charcoal is a water magnet. I have seen C with 10-15% water content that looked/felt bone-dry. Others have reported 25% water mass in dry-appearing C and I believe them. KNO3 always gets cooked, too, though it can only absorb around 2% additional mass in water (i.e., mildly hydrophilic)

For cooking water off of chems in a gas stove, you need to vent the oven frequently (just wafting the door open/closed a bit periodicaly) to remove water vapor that is released from the gas burning or it will just get sucked right back up into your chems. Same for C, KNO3, & strontium nitrate. That's all the chems I ever bake, but do so always, for all three.

Early early on I had a few episodes of BP clumping in the mill. Fixed that pronto and have never, ever, had it happen again. Dry chems is the solution. Failsafe.

Clumped BP in mill does NOT equal a 'finished' batch. Ever. That's a stupid myth that should die. Clumped BP in a mill indicates poor technical practices.

January 8

The level of diminishing returns is definitely different between pyro uses and firearm uses. The bore and projectile weight/fit are vastly different. The larger bore and heavier projectiles in some ways give pyrotechnics more leeway. It's probably not so much that the powder doesn't continue to improve with milling for 24 or 48hr, it more that the effect isn't really noticeable and doesn't become worth the additional processing.

There are a few extra things you can try to dry out to help prevent clumping. Some people will throw a dessicant packet in with their sulfur. Sulfur on it's own is actually quite hydrophobic, but depending on the grade it can have small amounts of additives or impurities that can cause it to absorb a little bit of water. Others have had success making sure their mill barrel and media are also dried. Sitting it out in the sun for a few hours once it warms back up some might help.

Have you possibly tried other charcoal sources? It should be fairly dry coming straight from the retort, but nearly all woods have some level of resins and waxes that might eventually be rearing their heads. A higher temp or longer cook may also be beneficial. Again, these are not things that probably impact pyrotechnics much but with lengthy mill times to produce firearm grade powder it could become more of a factor.

January 9

You say "from the retort". Are you actually using a vented retort, are you using a TLUD or similar setup?

Past discussion mentioned the possibility that the sulfur is becoming a binding agent, especially when milling in hot environments.

Edited January 9 by FrankRizzo

January 10

I wonder about the quality of the potassium nitrate. It wouldn't be prills, would it?

One thing that was suggested to me to address clumping was to add a couple of pieces of extra large media, theoretically to break off any buildup that starts to form on the mill jar walls as it forms. It seemed to work for me in the few times I had clumping concerns. I wouldn't have a need to mill powder for more than 4 hours though.

The BP pump set in the picture is what I used to make pucks of a specific density with my 20 ton press. I'd use a weighed amount of powder with a weighed amount of additional water to press a puck of a given thickness. The guy's setup for making pucks on the Everything Black Powder YouTube channel is pretty loosey goosey tbh, considering that he's looking for maximum uniformity powder for firearms use. This particular set is for 1/2" thick pucks, and could easily be altered to make pucks that are thinner and easier to break up. The burn rate of BP goes down quite a bit if it's pressed to too high a density, so I think density would be worth considering when making ballistic powder.

January 10

I just pick up my rubber jar every so often and whack it with a stick 😆

Edited January 10 by Richtee

January 11

14 hours ago, Richtee said:

I just pick up my rubber jar every so often and whack it with a stick 😆

So simple, yet so effective. I used to do that when using the PVC mill jar. The rubber lined rebel mill jars are a dream though, provided you made a decently aligned mill.

January 11

18 hours ago, DavidF said:

I wonder about the quality of the potassium nitrate. It wouldn't be prills, would it?

One thing that was suggested to me to address clumping was to add a couple of pieces of extra large media, theoretically to break off any buildup that starts to form on the mill jar walls as it forms. It seemed to work for me in the few times I had clumping concerns. I wouldn't have a need to mill powder for more than 4 hours though.

The BP pump set in the picture is what I used to make pucks of a specific density with my 20 ton press. I'd use a weighed amount of powder with a weighed amount of additional water to press a puck of a given thickness. The guy's setup for making pucks on the Everything Black Powder YouTube channel is pretty loosey goosey tbh, considering that he's looking for maximum uniformity powder for firearms use. This particular set is for 1/2" thick pucks, and could easily be altered to make pucks that are thinner and easier to break up. The burn rate of BP goes down quite a bit if it's pressed to too high a density, so I think density would be worth considering when making ballistic powder.

I wonder if another contributing factor is the charcoal consistency. Light and fluffy never seems to clump as long as it's dry (moves like water and gets airborne when disturbed too much). I've had charcoal come out of a retort, get milled, then lose another 13 - 15% (+/- it wasn't super exact) weight in a drying box over night (mainly with weeping willow charcoal and red maple). I don't know - so many factors.

January 11

All kidding aside, just because one (or two) pyros are OK with whacking a jar of BP with a stick doesn't mean it's safe. I would never do it, even once. A Florida pyro had a BP mill explosion from large ceramic media clacking together while milling. Also, BurritoBandito shook a jar of BP with glass marbles in it and it blew up in his hand.

From Dagabu:

"I just got off the phone with Burrito Bandito, he is in the hospital with some second degree burns and is missing his right pinky finger when his ball mill jar exploded late on the 4th of July when he was tending the jar after it caked up on him.

BB was using glass marbles as his grinding media and a Harbor Freight rock tumbler rubber jar with the aluminum cap. When the jar became caked, he shook the jar to dislodge the caked BP and the jar exploded in his hands. I am sure there are other injuries and I am sure he is still very much in shock but he wanted me to share this with all of you as soon as i was able to implore you all to NEVER use glass marbles for media, to never shake or hit your jars and to always wear your PPE!"

Just sayin'...

January 11

Well... I have only ever used lead, now brass media. I’d be leary of ceramic and would never use glass. And of course the rubber jar flexes a bit, absorbing some of the shock, and deforming a bit to help break up the clumping. I’d have to think any mill jar explosions were the result of the media. I’d also never use a PVC jar. That’s just a grenade invitation. That rubber jar might pop a bit, but flame would be the main result.

January 11

3 hours ago, Richtee said:

Well... I have only ever used lead, now brass media. I’d be leary of ceramic and would never use glass. And of course the rubber jar flexes a bit, absorbing some of the shock, and deforming a bit to help break up the clumping. I’d have to think any mill jar explosions were the result of the media. I’d also never use a PVC jar. That’s just a grenade invitation. That rubber jar might pop a bit, but flame would be the main result.

With the PVC jars there is a rubber gasketed lid that doesn't screw on. It just has a mechanism to squeeze the rubber gasket pushing it against the rim of the jar and closing it that way. In my mind, you'd have close to the same mitigation of the end being blown off since B.P. has a "heaving" deflagration vs. a true "shattering" detonation.

**However, I admit that banging on the side of a mill jar is not the best course of action. I also agree that using glass media is also a horrible idea. I've never used ceramic media, but have read about the sparking risk from it.

January 11

1 hour ago, cmjlab said:

With the PVC jars there is a rubber gasketed lid that doesn't screw on. It just has a mechanism to squeeze the rubber gasket pushing it against the rim of the jar and closing it that way.

Same with my rubber jar. You tighten a wingnut, expanding a rubber gasket. No threads. All you’s possibly get is a pop and a WOOSH.

January 11

Guys.. is your BP so poor quality as to be a woosh? Unless you have an ignition in the very early minutes of a mill run, it's going to be an explosion.

Monday at 04:34 AM

On 1/11/2025 at 3:05 PM, FrankRizzo said:

Guys.. is your BP so poor quality as to be a woosh? Unless you have an ignition in the very early minutes of a mill run, it's going to be an explosion.

You seen mine. No slouch. It’s not a bomb. Now, err on the side yer comfortable with. I whack my mill bottle with a stick.

Monday at 04:36 PM

On 1/11/2025 at 3:05 PM, FrankRizzo said:

Guys.. is your BP so poor quality as to be a woosh? Unless you have an ignition in the very early minutes of a mill run, it's going to be an explosion.

I don't really feel like arguing about this, there is plenty of information on ball mill safety on here. I admit that certain practices carry more risk. I will also say that aside from a purposely lit ball mill for testing, I've not read about any ball mill explosions related to them going off during the milling of B.P. (when all appropriate measures were taken). I've read plenty about people using glass, milling metals, etc, then having an incident. None about a ball mill going off during milling of B.P.

Again, I am not saying you should throw caution to the wind. Each one of us will have to make their own decisions based on what people tell them, and take their own risks. Nothing about what I've ever provided has suggested that you should do anything I've done, and I do my best to never provide unsafe suggestions for milling practices. I will also admit when I'm wrong (as I did about banging on a jar with a stick).

As to whether or not a mill jar would explode or not based on the lid, I can't say I'm too concerned as I always prepare as if it will, and ensure that nobody and no property will be hurt if it does. If you're not milling that way, you have no business milling anything flammable at all.

Edited Monday at 04:37 PM by cmjlab

Wednesday at 04:22 PM

On 1/13/2025 at 10:36 AM, cmjlab said:

As to whether or not a mill jar would explode or not based on the lid, I can't say I'm too concerned as I always prepare as if it will, and ensure that nobody and no property will be hurt if it does. If you're not milling that way, you have no business milling anything flammable at all.

Correct. If we're going to talk about ball mills exploding, please do so in a responsible fashion. There's not going to be a "popping of the lid" or other such nonsense. You're going to have an explosion. Prepare accordingly.

Thursday at 07:33 AM

15 hours ago, FrankRizzo said:

Correct. If we're going to talk about ball mills exploding, please do so in a responsible fashion. There's not going to be a "popping of the lid" or other such nonsense. You're going to have an explosion. Prepare accordingly.

Yet we ALL know about using BP for a burst.. straight up- not coated rice hulls, etc...is very difficult without stringent containment. Just saying. I’mma buy a rubber jar with a friction fit top to blow up. it’ll be lackluster. A threaded top on PVC is a grenade

2025-01-17T15:09:12Z

On 1/16/2025 at 1:33 AM, Richtee said:

Yet we ALL know about using BP for a burst.. straight up- not coated rice hulls, etc...is very difficult without stringent containment. Just saying. I’mma buy a rubber jar with a friction fit top to blow up. it’ll be lackluster. A threaded top on PVC is a grenade

I think it will be enlightening! Lloyd Sponenburgh did it many years ago, with his rubber-capped PVC pipe "Sponen-jars".

http://dave2.freeshell.org/ammo/bp60/the explosion of a ball milling jar.pdf

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