HDPE Mortar Explosion

[MicroGram]

Hey guys I just wanted to show you whats left of a 4" HDPE mortar tube after an "incident" recently.😂

I also posted this in the Discord channel. But long story short, I recently switched to using Hemp coal instead of Willow. Initially I thought they were of relatively equal strength, just based on burning small piles on camera. However, when I actually started shooting the shells I noticed this powder had quite a bit more power. My shells were going noticeably higher then usual. I usually use 10% lift for my shells, and a little less for salutes; around 8%.

Anyhow I shot a few diff shells, then shot a salute filled with 150g 7/3 (50/50 Indian Blackhead/325 Bright Flake), plus a bit of puffed rice to top it up. Spollette either got rammed in (I glued both sides of the hemi then glued again after the gummed tape) or it compacted/ruptured and or sheared in half. My first flowerpot and it happens to be a salute.🤣

I don't think my shells were particularly under pasted, but something clearly went wrong! 🤷‍♂️

However the HDPE tube did its job very well. It stretched and twisted instead of fragmenting into hazardous chunks. There was almost no trace of the 5 gal bucket of sand i had the tube in, besides the base.

Stay safe everyone!

 

 

[cmjlab]

Are you using 75/15/10 (KNO3/Hemp Charcoal/Sulfur)?

[Richtee]

Yeah..that ain’t easy to do. Well, unless on purpose

[Guest]

I’m thinking last night should be blamed on the moon.🤪

 

[MicroGram]

On 12/1/2023 at 5:41 AM, cmjlab said:

Are you using 75/15/10 (KNO3/Hemp Charcoal/Sulfur)?

Yessir was regular BP. Granulated.

[cmjlab]

Thanks, that's interesting.  

[Arthur]

Bigger granules may help, Be very sure that the shell is well sealed by the fuse inside the lift cup, use extra glue or hot melt adhesive (piles of it!). Try 10 or 20% less lift,

[MicroGram]

On 12/6/2023 at 1:45 PM, Arthur said:

Bigger granules may help, Be very sure that the shell is well sealed by the fuse inside the lift cup, use extra glue or hot melt adhesive (piles of it!). Try 10 or 20% less lift,

Yep I was using thick PVA but I'm back to using hot glue again. Thick dabs on both sides of the hemi at the spollette then another big dab of glue on the outside after taping. I'm also using less BP now, 6-7% seems perfect. No problems since that one "incident".  😂

Regarding granule size, my last batch of BP actually did have more fines then usual. I've only granulated BP a few times now, and the last batch had a little bit less water then it should have when I granulated. I debated sieving out the fines and re granulating it, but it's only a kilo or so. Just going to adjust how I use it and try to avoid that many fines in the future. 👍

 

[Arthur]

Get some mesh sieves, research the numbers and separate your BP into OFA, 2FA and 4FA and maybe 6FA. lift is usually coarser than the burst. 

Make a dam out of a half inch long, 1" diameter "tube" round the fuse(s) and fill it with hot melt glue. 

[Mumbles]

When you're making BP regularly, I'd suggest sieving it.  It might seem wasteful, or like you're losing material, but there's a use for basically any cut.  It's just not always the same use.  It will make things more predictable for lift at the very least.

I have always used something equivalent to 2 + 3 FA for lift. 2FA is -4+12 mesh.  3FA is -10+16 mesh,  I've usually used a wider cut of -4+16 for lifting smaller shells or something that can take the harder hit.  Big shells gets a coarser cut.  I use -16+30 as kind of a 4FA sub, for lifting small inserts or star tests.  I use anything -30 to make spolettes, for priming fuses or spolettes, priming comets, or anything that requires something fairly fine.  

When granulating through a 4 mesh screen, I generally get about 70-80% lift, 15-20% medium, and about 5% fines.  Everyone's mileage varies, but it might be helpful for reference.  

[Arthur]

Having different mesh cuts of BP is important, as is using them wisely. However it's not a destructive process. If you grate a damp lump than you can simply incorporate previous surplus cuts into the next damp lump. If you puck and corn then you can return unwanted cuts to that process. Lift is usually larger granules, as BP burns from the outside of the grains then big grains burn relatively slowly meaning a slower but sustained pressure spike in the mortar.

Are you certain that your shells are fully dry? All the paper and glue needs to be totally dry before it has all the strength to resist the lift. Make the same shell but leave it in a warm place for a week (to a month) to ensure that it is fully dry.

[MicroGram]

Yes in the future I'll start sieving and grading the powder. It's ironic because I planned on sieving it and actually started doing so (just sieving out the fines to start) but decided against it and threw it back, as I don't yet have all the screens I'd like to. I did make some more screens since I made that batch of BP however, and have some other sizes of mesh on the way. 👍

I'm quite sure my shells are dry, though they rarely sit for more then a few days before I fire them. I always make sure each layer of tape dries a bit before I apply another. Usually just by making a few shells at a time and placing them in a dry, warm area with air movement in between layers helps with that. Also its quite dry here.  Even D1 cut stars dry out completely in just a couple days!

Here's the latest shells! Two D1 and two salutes, one perc and one nitrate. I fired them this evening. No incidents or unexpected explosions!😂

And here's some vids of the shells! I was experimenting with a prime which turned out very poor, as only one of the comets ignited! 

https://www.youtube.com/shorts/Zm5pA58vCs4

https://www.youtube.com/shorts/xsr8KRDDD78

 

Edited December 13, 2023 by MicroGram

[Zumber]

4 hours ago, MicroGram said:

Yes in the future I'll start sieving and grading the powder. It's ironic because I planned on sieving it and actually started doing so (just sieving out the fines to start) but decided against it and threw it back, as I don't yet have all the screens I'd like to. I did make some more screens since I made that batch of BP however, and have some other sizes of mesh on the way. 👍

I'm quite sure my shells are dry, though they rarely sit for more then a few days before I fire them. I always make sure each layer of tape dries a bit before I apply another. Usually just by making a few shells at a time and placing them in a dry, warm area with air movement in between layers helps with that. Also its quite dry here.  Even D1 cut stars dry out completely in just a couple days!

Here's the latest shells! Two D1 and two salutes, one perc and one nitrate. I fired them this evening. No incidents or unexpected explosions!😂

And here's some vids of the shells! I was experimenting with a prime which turned out very poor, as only one of the comets ignited! 

https://www.youtube.com/shorts/Zm5pA58vCs4

https://www.youtube.com/shorts/xsr8KRDDD78

 

Very nice shells MicroGram...!!

To ensure prime on comets I prefer black powder slurry and coarse bp granules It works just fine.

I love your shell pastings.

Can you provide more details on how you paste shells. Any diagrams and more detail process?

I have refered shell pasting article and diagram from Shimizu book  "FAST" but not clearly understood. Also refered lots of youtube videos but clear information is not shown.

Edited December 13, 2023 by Zumber

[MicroGram]

18 hours ago, Zumber said:

Very nice shells MicroGram...!!

To ensure prime on comets I prefer black powder slurry and coarse bp granules It works just fine.

I love your shell pastings.

Can you provide more details on how you paste shells. Any diagrams and more detail process?

I have refered shell pasting article and diagram from Shimizu book  "FAST" but not clearly understood. Also refered lots of youtube videos but clear information is not shown.

Thanks Zumber. Regarding taping, I just do 3 or so layer of strips of tape, alternating poles and whatnot. Then a couple layers doing a "continuous strip" method, like a taping machine would do, which is quite a bit more then a regular layer just using strips. I really have no idea how to describe it beyond that!

[Zumber]

54 minutes ago, MicroGram said:

Thanks Zumber. Regarding taping, I just do 3 or so layer of strips of tape, alternating poles and whatnot. Then a couple layers doing a "continuous strip" method, like a taping machine would do, which is quite a bit more then a regular layer just using strips. I really have no idea how to describe it beyond that!

Okay Thank you for response...!!😊