Lift charge calculation

[BillyBobBodean]

I am using home-made granulated BP for lift charge. My initial test with a baseball (at 148 grams weight) I used 10% (15 grams) of lift powder in a 3" mortar. I was very pleased with the result, I got about 300 ft. of lift. My question is, do I just use 10% for bigger shells. If I have a 6" shell that weighs 800 grams do I use 80 grams of lift? I don't want to blow the shell apart in the tube. Thanks!

[Arthur]

It's all part of the shell design, your design, and of course your powder comes into it too!

 

With a good fitting shell in mortar 10% should lift a 3" but as the size increases the proportion decreases. The one rule of thumb "an ounce per pound" leaves small shells bursting low and big ones ( 10", 12", 16") bursting in outer space.

 

If you need more than 15% to launch a 3" then look at the mortar length (should be about 5 x it's bore,) or powder speed and strength.

[Jordan123]

Me, i use 7% of the weight of my shell, for example :

Shell weight : 100gr

BP weight : 7gr

 

I use this and is very good for a nice BP granulated

[fredhappy]

#billybob: as shells get larger they need less lift!..

 

For instance, If you need about 12% under a 3", a 4"would need about 9.5% , a 5"er 9% and a 6"er 8.5%. These are the amounts I use myself. My lift isn't the most powerfull but it gets the job done.

 

Be sure to test out your own lift and take notes. Carefully note down milling times and the kind of charcoal you've used. Try to make everything standard and do not change anything once you have the lift dialed in.

 

I hope this helps,

 

best

 

fred

[eb11]

for my 2inch shells that weigh in at 136g i use 4 grams of bp

[Mumbles]

As others have indicated, there are so many variables. Larger shells need proportionally less lift. Tighter fitting shells will use the lifting power more efficiently so can tend to use less lift charge as well. Grain size of the lift also affects things. What works for big shells does not work for small shells, and vice-versa.

 

For my own powder, I use an ounce per pound (6.25%) if I am using 2FA, and probably around 10% if I'm using 4FA. The cutoff for where I use 2FA vs. 4FA comes around 500g. Typically I'll add a little extra if worried about fallout or at PGI.

[BillyBobBodean]

Thanks to all for the input, I appreciate it! It really helps clear it up for me.

[dynomike1]

It's all part of the shell design, your design, and of course your powder comes into it too!

 

With a good fitting shell in mortar 10% should lift a 3" but as the size increases the proportion decreases. The one rule of thumb "an ounce per pound" leaves small shells bursting low and big ones ( 10", 12", 16") bursting in outer space.

 

If you need more than 15% to launch a 3" then look at the mortar length (should be about 5 x it's bore,) or powder speed and strength.

Am i reading the rule of thumb right? I understand the heaver the shell the more pressure it will build up to move it. This is why i ask. My 4" dummy shell weighs 10.6oz, 2 oz of my bp will send the shell to its apex in 4 sec. A 3" weighs 3.4oz. and the time with .75oz.= 3 sec.. 1 oz.= 4sec..Both of these shells are loaded with Cotton seed. These are actual test. 5&6" are coming, maybe tomorrow.

 

3" shell=3.4oz.=.75 oz. bp=3 sec.

1 oz.. bp=4 sec.

 

4" shell=10.6oz.=2 oz. bp=4sec to apex

[Mumbles]

The ounce per pound thing really doesn't start working all that well until you get over a pound or two. To be fair, the total rule of thumb is "an ounce of lift per pound of shell weight up to 10lbs, then one half ounce of lift per pound of shell weight there after."

 

It was based off of a particular commercial grade of 2FA produced by Goex. The powder has since gone down in potency as the manufacturing plants have changed locations, and possibly charcoal sources. People in the know have recommended modifications, such as using 3/4oz per pound over 10lbs, or just using 1oz per pound across the board. Others have suggested to use slightly more, such as 1.25oz per pound of shell weight. It really comes down to knowing your lift if it's homemade, and understanding that small shells will need more lift and/or a finer grain size of lift.

 

I personally use 4FA at around 10% for shells less than a pound, and 2FA at the ounce per pound (6.25%) rule of thumb, but generally round up to the nearest half ounce, for shells over a pound,

[ollie1016]

Has anyone tried black powder coated rice hulls for lift? Edited July 12, 2013 by ollie1016

[Seymour]

Yes. They work well. I'd consider them similar to rough powder- as in, they burn faster than pressed grain, and with hot powder you've got to take care with quantity.

 

I personally don't see a lot of benefits though, other than the simplicity of using one thing for burst and lift. I get this, but I just do away with hulls and use rough granulated BP for lift and burst.

[Mumbles]

It's easy to use the same thing for burst and lift, just make cylinder shells. It's these guys making ball shells that are screwing themselves up.

[ollie1016]

It's easy to use the same thing for burst and lift, just make cylinder shells. It's these guys making ball shells that are screwing themselves up.

 

Mumbles, what ratio do you recommend for bp coated rice hulls? 3:1? 6:1? Thanks

[Mumbles]

It's been a while since I've made any, but I think I used to use 5:1.

[TYRONEEZEKIEL]

I make 7:1 for my 3" shells, and do 5:1 for my 4"s

[ollie1016]

Any recommendations for 2" shells burst?

[Carbon796]

For burst charge ? BP rice hulls + about 1.5 grams SFB

[ollie1016]

Sorry Carbon, I wasn't very clear at all. What ratios of BP to rice hulls would you use for breaking a 2" shell? I am starting to get some kind of spherical break on my shells now , and I'm fed up of using gran BP as a filler. I have made 1:1 Bp coated rice hulls, and they are very weak. In the open they burn like slow meal-d! Just wondering if you use different ratios for different sized shells? Ollie

[Carbon796]

Most people stay in the 4:1 to 7:1 range. Most shells under 5" will benefit from a booster or need a booster. Even with straight BP in a 2" you will probably need a booster for a good break. Or add more confinement if you have enough room with your mortar. There is only so much room left in a 2" shell after stars are added that the BP to hulls ratio won't matter too much. Edited July 25, 2013 by Carbon796

[pyroman2498]

Any recommendations for 2" shells burst?

What i use is 5:1 Bp to Rice hulls, with about 1-2g of whistle.

 

For my smaller cylinder shells i use just rice hulls , for my 2's and up i use granulated/corned BP.

[Livingston]

Ive usually use %10 of the shell weight.. but im curious to know how much lift i should use for my 6's.. I have a few made but not sure I how much i need. the 2 shell weighs 1275g..any help will be mostly appreciated!!! thank you

[Sulphurstan]

Question about lifting comets.

 

I've been reading that the lift charge for items less than 10 lbs is -rule of thumb- 1oz for 1 lbs.

Does this also apply for very small items, like 5 grams comets (0,17 oz)?

 

That would mean lifting my comet with as little as 0,35 grams (0,012 oz)! This sounds terribly little to me: looks like a pinch only!

 

I understand that it all depends on grain, hot or "cold" BP, grain size etc etc. But i just want to know if there is also a rule of thumb for this very light weight items ...

 

Thanks in advance.

[memo]

on a shell of that weight I would use 1 oz. per pound of 2 fa or larger or about 79 grms. of lift of good lift powder

[stix]

on a shell of that weight I would use 1 oz. per pound of 2 fa or larger or about 79 grms. of lift of good lift powder

 

I think you got the weight mixed up memo. Sulphurstan is talking about a 5 gram Comet.

 

@Sulphurstan

 

My standard comets are 17mmID (6-7) grams inserted into a 19mmID tube.

I used 1.7grams of hot home-made 4FA for lift. The comet went up approx. 25mtrs (80ft) - which was pretty much perfect for my glitter composition.

 

I'm not sure if there is a "rule of thumb", but Col on this forum helped me to work out Lift/Comet/Endplug etc. for my star gun - he may also have given advice on the amount of lift required. I tried to search for the post but couldn't find it.

 

Hope this helps in some way.

 

[EDIT]

 

Found the link: https://www.amateurpyro.com/forums/topic/10445-attempting-my-first-star-mine-questions/

No real info on the rule of thumb for lift, and I was using 1/4" cut stars in a 19mmID tube and since have moved on to comets. Still, there may be some worthwhile info.

 

Cheers.

Edited February 24, 2018 by stix

[Sulphurstan]

Hi Stix.

This is EXACTLY the Kind of information I was looking for, for comets gun and stargun also.

Thank you!