Fence Post Prime Question

[deepdixie]

Greetings friends!

 

As a fairly new shell builder I have learned through trial and error that Perchlorate based stars are hard to ignite, especially with a BP prime. I plan on priming my next batch of Perc stars with Fence Post Prime. A formula I have read about here and elsewhere for Fence Post consists of the following:

 

Potassium Nitrate - 65

Air Float Charcoal - 15

Sulfur - 10

Diatmaceous Earth (pool grade, coarse) - 5

Silicon - 5

Dextrin - 4

 

Can the Diatmaceous Earth be substituted with Wood Meal without compromising the performance of this prime that has a reputation for igniting even hard to light stars?

 

Has anyone ever had to add a BP prime layer to the Fence Post for any star comp?

 

Thanks

[Bobosan]

I think you would be okay with the wood meal. It should be very fine though.

 

I've tried the fencepost prime with some perc blue stars and although the prime burned successfully it still did not ignite the stars consistently. I step primed over the fencepost with the perc comp and BP and finally got consistent burns. Eventually went to monocapa prime but still requires a BP prime. Working with rolled Shimizu blue.

 

Mumbles as mentioned that perc based blue stars have a nasty habit of blowing blind.

[deepdixie]

I am working on Blue Perc stars at the moment strangely enough. I have had several shells perform quite well with only a heavy BP prime on the Blue stars, while other shells blew completely blind with no star ignition at all. I will double coat the Blue stars in the future, first with Fence Post and then BP.

[psyco_1322]

Fence post prime should not need any prime layer over it. That's one of the pluses to it. Perc blues are not very vigorous burning stars, so it's not uncommon to have issues. If you were to cut the stars, they may light and stay lit better.

[Bobosan]

Fence post prime should not need any prime layer over it. That's one of the pluses to it. Perc blues are not very vigorous burning stars, so it's not uncommon to have issues. If you were to cut the stars, they may light and stay lit better.

 

Thanks pysco. I can see the fencepost burning when it leaves the gun but fails to ignite the rolled star. Haven't tried to cut any yet. That's next on the "to do" list for these blues.

[psyco_1322]

I've always had bad luck testing from star guns too, they always seem to blow stars blind randomly. Maybe I over load the lift, but I like testing in shells or mines.

Edited July 20, 2014 by psyco_1322

[marks265]

DE is also another form of silicon. I can't remember if it is the same or a variant. I always called DE crushed dinosaur bones.

[jessoman]

I thought DE was primarily SiO2, silica, or silicone dioxide and other matter. In a prime they have different characteristics. The slag from the high temps that form with SiO2 get fire to the star and keep it lit. Also offer an irregular and pretty hard burn surface, aiding in ignition. Considering it's high percentage of SiO2, it may be worth trying to blend up kitty litter crystals and subbing . Just a thought! I'm not sure if wood is the go.

Concerning silicon metal, it's characteristic in a prime is a hot fuel.

This is what I have read anyway.

In your question OP, FP is a standalone prime usually. But there is no harm in throwing BP over the top. Even just a dusting. I do it, never had a blind star in my life. Regardless of star gun or super hard break. I believe there are a few tricks, but they depend on the actual chems your using and how they relate to how a prime works. or. Taking fire, temp, slag etc.

 

Concerning blue, they have to light and stay lit as has been mentioned. Blue stars can blow out and this is thought to be due to the burn temp being lower.

[psypuls]

KCLO4 67
Charcoal 14
Red gum 9
Silicon 5
Dextrin 5

Wouldn't this perform just as good?

[Sparx88]

Perc blues were the first colored stars I started learning with and after many trials and errors, this is what I have been doing that works for me.

 

Star comp, is a tweaked Hardt blue #6 Mumbles came up with awile back that I have been using since.

 

Potassium Perchlorate - 62
Sulfur - 18
Copper Oxide - 12
Parlon - 4
Dextrin - 4
Addition of aluminum not critical, only if want bright sparks
Aluminum - 5 (I add 4% dark flake and 2% firefly flake or 30-60 mesh.)

 

 

The prime that I came up with that lights these stars well;

 

50 PPerc

25 BP meal

5 granulated bp (lift) adds the rough texture

15 drk alum

8 sulfur

3 dextrin

 

I spritz the stars with 70% isoprop while rolling around in a ceramic bowl and add the prime until 1-2 mm thick. I don't have silicon, I would use that if I did, but this here is what works for me with out it. So adding some would'nt hurt.

 

heres a 2" shell with those stars with that prime done on the 4th this year, video quality is bad but you can see even lighting on the stars.

 

http://www.youtube.com/watch?v=xhr6Ej12D9w

 

 

[Bobosan]

Sparx,

 

You mentioned rolling the prime onto the stars. Did you also roll on the star comp?

[Mumbles]

KCLO4 67

Charcoal 14

Red gum 9

Silicon 5

Dextrin 5

 

Wouldn't this perform just as good?

 

 

That is basically just pinball prime. It works well, and is the prime I generally use. It does require a layer of black powder over the top to ensure it lights well though.

[schroedinger]

Why don't you try to use wood meal. For example veline prime uses it to rough up the structure. Did you try veline prime?

[psypuls]

 

 

That is basically just pinball prime. It works well, and is the prime I generally use. It does require a layer of black powder over the top to ensure it lights well though.

so it is absolutely required to use an outer layer of black powder? screened ? or ballmilled meal?

[nater]

I would not say it is ABSOLUTELY required, but a final layer of BP is the best practice. Use screen mixed BP as the slag helps pass fire to the layers and not milling the powder leaves a rougher surface which aides ignition.

[gun410]

I would use green mix it works for me

[Bobosan]

I've always had bad luck testing from star guns too, they always seem to blow stars blind randomly. Maybe I over load the lift, but I like testing in shells or mines.

 

psyco, you do piston or bag mines? Been thinking on trying a piston mine for height. Stars keep getting bigger and bigger as I roll more primes.

[marks265]

I thought DE was primarily SiO2, silica, or silicone dioxide and other matter.

 

I believe you're right Jess. I knew there was a difference, I just couldn't remeber what in the midsts of another pet project or two.

Mark

[jessoman]

Bobosan, Pistons are great for achieving decent height. The are extremely simple and quick to make with a bit of hot glue.

 

I would use green mix it works for me

 

gun410, please do not give advice to people. Especially without any explanation. Considering you are so new you have demonstrated your actions could be dangerous to yourself, please do not make your advice dangerous to other. Just thought I would nip it in the bud. In this case it will not likely be dangerous, unless it is a chlorate star.

[Sparx88]

Sparx,

 

You mentioned rolling the prime onto the stars. Did you also roll on the star comp?

 

 

I used a single 1/4" pump, cylinder. Wood hammer to wack'm tight and dried them in a dehydrator at 125 F 24 hrs or so. then when dry added the prime.

[nater]

The sentiment is true, but your statement is not entirely true.

 

 

gun410, please do not give advice to people. Especially without any explanation. Considering you are so new you have demonstrated your actions could be dangerous to yourself, please do not make your advice dangerous to other. Just thought I would nip it in the bud. In this case it will not likely be dangerous, unless it is a chlorate star.

[Bobosan]

 

 

I used a single 1/4" pump, cylinder. Wood hammer to wack'm tight and dried them in a dehydrator at 125 F 24 hrs or so. then when dry added the prime.

 

Thanks Sparx. Going to try a poor man's 1/4" pump first before ordering one. I keep having this nagging feeling that rolling these perc blue stars is not the best way for a hard to light composition.

[psypuls]

 

 

That is basically just pinball prime. It works well, and is the prime I generally use. It does require a layer of black powder over the top to ensure it lights well though.

So what kind of black powder over the top, I screened bp 10 times for a green mix/scratch mix and it hardly ignites.

I don't think I've ever made green mix before so I don't know how it's supposed to be

because when I try to set it on fire, I have to burn it for a long time before something happens, then it just smolders slightly and goes out, and i have to re-ignite it, the long ignition time worries me, i even did it with a torch light. is this what the final layer should be like? or do i make meal with the ball mill first? also +5 dextrin, any Si?

Edited July 21, 2014 by psypuls

[psyco_1322]

So what kind of black powder over the top, I screened bp 10 times for a green mix/scratch mix and it hardly ignites.

I don't think I've ever made green mix before so I don't know how it's supposed to be

because when I try to set it on fire, I have to burn it for a long time before something happens, then it just smolders slightly and goes out, and i have to re-ignite it, the long ignition time worries me, i even did it with a torch light. is this what the final layer should be like? or do i make meal with the ball mill first? also +5 dextrin, any Si?

 

Green Mix

Finely powder potassium nitrate - 75

Airfloat charcoal - 15

Sulfur - 10

Dextrin - 5

 

Screen this 3-4 times through a 30-40 mesh screen. Apply as needed. It's essentially just unmilled bp. You obviously should have everything powdered, no coarse charcoal, no granular nitrate, it won't burn like that. If you are still having troubles, I suspect you have an issue with your chems.

[schroedinger]

If your green mix doesn't burn on itself, you also could make a quite similar powder by adding everything to you mill and mill just for 10 to 30 minutes. This is no real green mix, but works similar.