Hobbyist mill BP

[justvisiting]

Hey folks, this is my latest run of BP tests, which I don't think I've posted here previously. It examines issues of mill times, screen-mixed vs. 3 component-milled powders, and moisture levels when pucking. The lift performances of six different powders were compared, using baseballs fired from a 3" mortar tube. Some folks may find something of interest in my write-up.

http://pyrobin.com/files/Black%20Powder%20six%20ways%20V.2.pdf

[ExplosiveCoek]

Thanks for sharing your work. I recall that some pyro's also used premilling the separate ingredients, and then finished it off by milling together for one hour or so. This was also done due to safety concerns when milling the complete live powder for a longer period of time

[MadMat]

I ran a bunch of baseball tests on my BP a few years ago as well. BP milled as a mix ALWAYS performed better. If the mix is run in an optimized milling procedure, peak performance occurred after four hours of milling. Any extra time was simply a waste of time. Now, I will never say that it is completely safe to mill BP as a mix, but, I have made literally hundreds, if not thousands of batches of BP without incident. Still, I run my mill inside of concrete blocks filled with sand. My "hardened bunker" for my mill is not sealed! It would be foolish to try to contain an explosion, but rather I try to direct the blast wave in a safe direction (in my case straight up). Now I have posted this before, but, I have found that making charcoal from wood that is semi-rotten, made dramatically superior BP. My tests also concluded that BP pressed into pucks and corned, on average, out performed BP that was made with a binder and granulated.

Edited November 15, 2019 by MadMat

[Arthur]

I like your work, it shows differences caused by method well. If you want to test a particular wood for charcoal then you need to do some tests with a well known wood, by the same method, for comparison.

[Mumbles]

Madmat, I'm curious what you think your results with semi-rotten wood tell. Do you think it gives an overall better product, or rather it just gets to optimal performance faster? Have you tried anything from the same source, rotten and "fresh"? I'd be curious to know if they give different results, and if the fresh wood can achieve the same level of performance, perhaps with a longer milling time.

 

David, great work as always. It's great to see actual numbers and testing being done to back up theories, instead of anecdotal evidence or general descriptions. I think it pretty clearly shows your pre-milling and screening method produces comparable powder to three component milled powders. I had a few questions. These are basically out of pure curiosity.

 

How closely grouped are the flight times, or rather what would you say is the standard deviation on the flight times?

 

How do these results compare with something made in the Rebel 17 mill, if you have something to compare?

 

How much of the nitrate, sulfur, and charcoal fail to pass the 40 mesh screen after milling?

 

What RPM does the smaller mill run at?

 

Do you think there would be diminishing returns for milling the charcoal longer than 6hr?

[MadMat]

I have compared charcoal made from both willow and red cedar in pristine and semi-rotted conditions. In every case, the charcoal made from the semi-rotted wood out performed the charcoal made from pristine condition wood in baseball tests. The difference was approx 1-1/2 to 2 seconds of flight time in the baseball tests. I posted a long time ago that the first time I made BP from rotted wood charcoal I used it for lift of a three inch shell in the same manner as my other BP and actually blew up my mortar tube (it was a cardboard tube, but still...) not to mention the star pattern of that shell looked decidedly oval as (as I believed) the shell was still in a rapid ascent when my time fuse went off. This is what prompted me to do the baseball tests to compare the different charcoals. I also learned to change my lift charge

Edited November 16, 2019 by MadMat

[justvisiting]

Thanks for the comments folks! My BP investigations started when a generous pyro wanted advice on making nozzleless rockets, but absolutely refused to mill black powder as a complete mix. That started me on the journey to produce screen-mixed black powder that rivalled commercial powder. Each set of experiments was done to examine specific aspects of black powder production and performance. If black powder were a jigsaw puzzle, I'd say I've got the corners done, and most of the perimeter, but there's a lot of the middle to be done yet. Since my investigations are done as 'stand-alone' examinations, I've not settled on an exact procedure that would allow comparisons between them in an apples to apples kind of way.

 

It is true that 3 component milling gives the longest flight times per amount of powder than any of my screen-mixed powders- but not by a huge amount. Hopefully by now I've shown that screen-mixed black powder is an acceptable option for those that can't (or don't want to) mill the complete mixture. I've milled plenty of black powder without incident myself. It's not like an accident inspired me. For me, it's not that I think my mill will explode, it's about the amount of time I spend worrying about the possibility, and the life-changing impact a mill explosion could have on me. Europeans don't have the wide open spaces we enjoy here in North America, so for many of them, single component milling is a less dangerous way to produce black powder.

 

Thanks for the endorsement Mumbles. I'll attempt to answer your questions.

 

1) How closely grouped are the flight times, or rather what would you say is the standard deviation on the flight times?

 

For each group of three flights, there is significant variation in the times. The greatest spread between the lowest and highest times for a group was 1.3 seconds! That's uncommon though, and may have been a mistake in the reporting. The least spread in a group was .25 second. The average spread for all the results in this investigation was .5 sec. That's still significant. Baseball testing is not the most accurate method for evaluating powder performance. However, it's easy, inexpensive, and uses easily accessible materials. Also, the powder is tested in a real world scenario, lifting a 'dummy' shell. Readers can easily understand the results, and reproduce the work if they so desire.

 

I've tried to pinpoint the reasons for such deviations. Some people just pour the powder into the mortar loose. That's sloppy work, and does not mimic the way the powder would be used to lift a real shell. The powder could all go to one side, the mortar could be damp inside, or residue from previous flights could affect results. I use identical lift cups for each set of tests, center the cup in the mortar tube, and use uniform lengths of black match to ignite the powder. I weight the powders on a triple beam balance now, just in case my digital scales were a source of inaccuracy in measuring. Still I get significant variations. 'My' 2FA grade powder (4-12 mesh) has a significant range of particle sizes, compared to 'my' 1Fg (12-16 mesh). The variations don't seem to be more or less with one grade, on the whole. The results could be affected by weather, so all my tests are done on the same day. Buildup on the mortar could skew the results, especially when testing slower powders. I wash and dry the mortar as necessary. I use the same baseball where possible, but after a few flights they get pretty ratty! I make sure the balls I use weight the same as each other, when using more than one. The mortar tube is mounted to a heavy steel base, which is placed on the same (level) spot for each test I do. I feel like I've covered all the common sources of error, and my times have tightened up some, but the inherent inaccuracy of the method remains, to quite a degree. My guess is that the stitching of the ball is the main culprit. I'd like to design a test that gives tighter results, but baseball testing is what is recognized as the best real-world method for powder testing, so I continue using the method. Doing 3 flights per powder type gives a pretty good picture of what to expect from a given type of powder, so I forge on with this popular method of testing.

 

 

How do these results compare with something made in the Rebel 17 mill, if you have something to compare?

I can only comment in a general way on this, as I haven't done apples to apples comparisons. A larger diameter mill jar definitely mills more efficiently. The flight times from my various sets of tests show this trend. There are other considerations besides jar diameter to take into account too, like jar shape and RPMs. I have no doubt that my average flight times would be higher if these powders had been prepared in larger batches in my larger mill.

How much of the nitrate, sulfur, and charcoal fail to pass the 40 mesh screen after milling?

What RPM does the smaller mill run at?

That's an interesting question. I received the mill for free for testing (as a gift) , and I've been hesitant to talk specifically about its performance. But since you asked ;

After milling 250 grams of crystalline potassium nitrate in this mill for 2 hours, +2 grams failed to pass 40 mesh. Using a new 250 gram batch of milled nitrate and a 100 mesh screen, 20 grams failed to pass. I was alerted to the problem when I noticed white specks in my first puck, which I had not seen before when milling with the larger (Rebel 17) jar. I had a similar problem when milling the pelletized sulfur I bought when my rubbermakers sulfur became unavailable where I live. The sulfur was passed through a 100 mesh screen before continuing. About 15% failed to pass. It's commonly known that a smaller mill jar will have less 'fall', and that longer mill times are necessary with small mill jars. However, I didn't think the difference would be so obvious and dramatic. The jar on this mill turns at just under 75 RPM. Lloyd's chart for optimal jar speeds (on Pyrobin) shows an ideal RPM of 92 for a mill jar of this diameter.

This sudden development was quite vexing. I decided to fabricate a larger diameter jar with the same internal volume as the jar that came with the mill. The new jar is 6 1/2" outside diameter and much shorter (pancake jar). The same charge of potassium nitrate and media was again screened. This time, all of it passed 40 mesh. Less than half a gram sat on 100 mesh. It's interesting that such an improvement was had, considering that the RPM of the new jar was only 25, a mere third of the original 75 RPM.

I screened more sulfur the same way and was not so impressed. I didn't record the results. In sheer frustration, I went out and got a Magic Bullet (blade mill), and used it to reduce the sulfur pellets. Well, THAT sure worked well! The blade mill did in a minute or two what the ball mill did in 2 hours. After that, I screened all my sulfur through 100 mesh after blade milling, and re-milled any that didn't pass, with the next load. Most folks wouldn't know that sulfur responds better to blade milling than ball milling, because most folks get their sulfur as an already fine powder. I imagine that ball milling the blade-milled sulfur that passed 100 mesh would reduce the particle size quite a bit further, and maybe increase baseball flight times a bit- but I didn't do it. I just used the -100 mesh sulfur 'as is'.

I can't comment on how much charcoal sat on 40 mesh exactly, since the charcoal used in these tests started as -12 mesh. I will say that when preparing my screen-mixed powders, I didn't see any dark specks on my 40 mesh screen.

Do you think there would be diminishing returns for milling the charcoal longer than 6hr?

I'm not sure. In a small mill jar, I think the charcoal would be milled finer with smaller diameter media than I used. Increasing the jar diameter would give an improvement too I think (even though the RPM goes down), based on what I saw with the potassium nitrate. For milling charcoal by itself, the best performance I've seen is with 5/16" stainless steel media. I chose 1/2" media for this run of tests, because it's what is already in common use by many pyros.

The manufacturer of the mill (Pyro-Gear in the UK) has now come out with a higher capacity mill that features a larger diameter mill jar, which runs at a higher RPM than my smaller one does with a larger jar on it. That's sure to be a nice improvement in efficiency over the original. I'm confident the smaller mill and jar could make powder just as good as what the larger mill makes- it would just take longer, is all.

[WillowPineAndBoom]

Did anybody try different compositions of bp ? Or everybody use the standard ratios ? I have try many comp ratios the fastest so far was 62k 20c 18s.kno3 was crystals the charcoal was pine and sulfur was oil factory rocks and milling about 1 hour(and all ingredients was pre milled for several hours separate)1 meters batch light in 1 second or less i think(not granulated)!If anyone try enother ratios please reply. I love to see something different and why not more powerfull! Happy Christmas to all guys and happy new year with our own pyros Edited December 25, 2019 by WillowPineAndBoom

[Boophoenix]

W&B, Dave ( Justvisiting ) has dabbled lightly in the area and I have to a much lesser degree. Different charcoal products can benefit from altering the ratios it seems. Charcoal particle size is one thing that can be overcome a little by fiddling with the ratios. Your ratio gives the hint your particle size may not have been milled real well just by looking at the ratios. Dave did an experiment with unmilled commercial airfloat to gain an acceptable lift height in which the ratio change was the main key.

I am of the belief that different source materials could benefit from slight changes and have felt that for some time now. I plan to do some testing in the area at some point while doing some other charcoal tests.

Richard H. and Ken G. from Pyro-Gear did some testing with ratios also and sped the burn rates up, but sacrificed performance if I recall correctly.

There are a whole slew of variables with charcoal as it is used in BP so I wonder how often we are comparing apples to apples when we start trying to compare our tests.

[Arthur]

Anyone reviewing the production of BP could well read any of the books on https://www.royalgunpowdermills.com/rgm-historic-reprint-series This is original data from the time when BP was normal war materiel and was made in different types for small arms right through to 16" naval weapons.

 

The e-books may suit non UK readers but the hard copies are good to read if postage isn't a problem.

 

Just remember that they made batches in the order of tons not pounds!

 

Big shells were propelled by 14mm AF hexagonal lumps of BP with holes through them, as the outside reduced the inside increased in surface area so the burn and chamber pressure were steadier than with just a granular powder.

[Boophoenix]

We have many listing for declassified military research papers in the US if you search around. I’ve found them interesting, but threw further research found some variables may be different. A paper I have on Swiss black powders talks about firearms BP being cooked at lower temps than that for fireworks.