25 replies to this topic

[pyroduck7]

hi i have some three inch shells ready for nov 5th but last year i did one and it bascially rolled out of the morter and went over the fence ( into a woods) and exploded there, litterally scimmed over the fence, this is my upmost fear ever since then i have put into the shells more than enough lift powder, but im just wondering - how much is too much? like what willl fllwerpot theshell#/ also i dont want to to bee too loud (naouboes probbley wont of herd that many cat4shells going off yards from there windows hahah) i know that the avg percentage ammount of bp to shell ratio is usally arround 10 - 12.5 percent but i have loaded up the shells with like 30 - 38 percent of the shells weight! ov corse safty is paramount but could my fearof putting too littlelift in a shell is a hazzord? i dont want a flour pot but nor do i want anouther innsadent of last year, i could do a dummy shell , with say - 15percent of the shell weight and just use a tenniss ball full with the respective weight in dirt?

please tell me your thoughts on this matter, and sorry if im making anouther post on what has alredddy been coverd, but i couldent find any!

[digger]

hi i have some three inch shells ready for nov 5th but last year i did one and it bascially rolled out of the morter and went over the fence ( into a woods) and exploded there, litterally scimmed over the fence, this is my upmost fear ever since then i have put into the shells more than enough lift powder, but im just wondering - how much is too much? like what willl fllwerpot theshell#/ also i dont want to to bee too loud (naouboes probbley wont of herd that many cat4shells going off yards from there windows hahah) i know that the avg percentage ammount of bp to shell ratio is usally arround 10 - 12.5 percent but i have loaded up the shells with like 30 - 38 percent of the shells weight! ov corse safty is paramount but could my fearof putting too littlelift in a shell is a hazzord? i dont want a flour pot but nor do i want anouther innsadent of last year, i could do a dummy shell , with say - 15percent of the shell weight and just use a tenniss ball full with the respective weight in dirt?

please tell me your thoughts on this matter, and sorry if im making anouther post on what has alredddy been coverd, but i couldent find any!

You win First prize for the worst spelling I have ever seen, boy was that difficult to read (was this spelling on purpose).

Anyway to answer your question. The usual rule is 1 ounce per pound of shell, but it all depends on the grade of powder and how good it is. I would use about 20 grams of a decent 2FA, but you may need up to 30 grams depending on weight and quality (assuming you have decent BP).

[Arthur Brown]

Well in answer to what I think you meant to write;

If 6 - 10% lift weight to shell weight doesn't work for you then your lift is no good, simple. what is the break charge like?

If you are planning to launch shells "yards from the neighbour's windows" you are bringing the whole fireworks hobby into disrepute. A 3"(75mm) mortar should be 75metres from any person, vehicle or structure. No debate on that figure, so those "yards" better be all of 75yards.

[digger]

Well in answer to what I think you meant to write;

If 6 - 10% lift weight to shell weight doesn't work for you then your lift is no good, simple. what is the break charge like?

If you are planning to launch shells "yards from the neighbour's windows" you are bringing the whole fireworks hobby into disrepute. A 3"(75mm) mortar should be 75metres from any person, vehicle or structure. No debate on that figure, so those "yards" better be all of 75yards.

I guess it depends on the size of the shell to the % of lift.

The bigger the shell the less lift is required as a percentage of the weight (also as shell size increases the powder speed needs to decreased).

Ultimately there is not an exact answer, as the amount used will depend on the grain size. A bigger grain size will require more powder than a smaller grain size.

So go and shoot some dummy shells in a nice wide open space and time the flight time for different powder grades and amounts. This will allow you to optimise the break height for your shells.

[CCH Concepts]

You win First prize for the worst spelling I have ever seen, boy was that difficult to read (was this spelling on purpose).

Anyway to answer your question. The usual rule is 1 ounce per pound of shell, but it all depends on the grade of powder and how good it is. I would use about 20 grams of a decent 2FA, but you may need up to 30 grams depending on weight and quality (assuming you have decent BP).

ha ha, i knew there had to be someone that had worse spelling than me.

but on subject, whats everyones thoughts on using benzolift. I've read about it and some people love it and some people see it as cheating. whats everyones thoughts.

[Arthur Brown]

Having once seen the unrolled remains of a mortar tube which failed when subjected to whistle misused as lift, which wasn't good. PLEASE follow tradition and use good BP for lift until you are competent enough to develop ideas of your own and have the space to do so.

If your lift is no good then your BP is no good, so you are not ready to make display shells.

[digger]

Having once seen the unrolled remains of a mortar tube which failed when subjected to whistle misused as lift, which wasn't good. PLEASE follow tradition and use good BP for lift until you are competent enough to develop ideas of your own and have the space to do so.

If your lift is no good then your BP is no good, so you are not ready to make display shells.

Would that have been at a certain event where someone abused one of my mortar tubes per chance (with a salicylate whistle, one of the more pokey versions)?

Benzolift can be used on small shells in limited quantities, however it can go high order if larger amounts are used so it should not be used in anything other than small quantities.

Ultimately get your BP consistent and then there will be no issues.

[cooperman435]

it was a good demo of what not to do though ?

[Mortartube]

Firstly is your lift BP granulated. I.e has 5% dextrin added and dampened then pushed through a sieve and dried. If not that is a problem straight away.

Is your BP as fast as this? If it is much slower then that is also your problem.

[seymour]

Pyroduck, I know you have many answers, but I will add mine too, hopefully without adding any coonfusion.

You seem to be worried that by adding too much lift, your shell may not survive the violence of being shot out of the mortar. It is true that large shells (three inch shells are definitely in the small shell catagory here), as well as poorly made shells (especially canister shells) are liable to not make it out intact. However, a well made three inch ball shell is going to be very hard to damage due to too much black powder lift. Indeed, I have sent them up with up to 200g of lift, and they still survived, though they break at a height that makes them look piddly and pathetic, especially after the thunderous lift boom.

I will elaborate on the factors that make a 'good three inch ball shell'.

The shell must have internal structural integrity, which means that the contents must be packed tightly (which is why shells are sliggtly over-filled with burst, before they are closed- with dificulty. They should not rattle when you shake them.

They should have a very strong case. This means that they are pasted well, with good paste soaked kraft that lays flat over the shell. Make sure that there are sufficient layers, and that they have dried before firing. Patience is a necessity in this hobby, and i do understand how frustrating waiting can be early on.

Lastly, you need to ensure that there are no gaps around the timefuse. These gapsa need not be visable to cause problems, so taking precautionary action is much more advisable than looking to see if it seems ok. One very good method that is often employed on commercially produced shells, is to wrap paste-soaked string (all natural fibres, none of the synthetic crap) around the timefuse, forming a conical mound over where the timefuse meets the shell casing.

However, just because a shell can be made to survive excessive lift does not in any way mean that using excessive lift is an alternative to quality lift. Just because the shell has a very high chance of surviving lift, does not mean that you should expect it to. Consider the worst possible outcome, and make sure that only means the loss of your firework.

[Arthur Brown]

Weak lift is likely to be slow lift, If you have a small slow fire in the bottom of your mortar then you have a good chance of cooking or burning the actual mortar tube. If the lift is good you need less, so less heat is made and the mortar tube will be safer, you will get a better lift, and the shell will break at the right height.

[a_bab]

For a 3" shell you need something like 10 grams of commercial BP. With homemade, I'd go for as much as 15 grams. If more is needed, then try to get a better bp.

As someone said, being able to make good quality bp is one of the first skills to be learned. I can't understand how people are not able to get it (it's because of the mill for sure), but if you are serious about this hobby a mill is one of the basic tools.

Edited by a_bab, 11 October 2009 - 03:41 PM.

[PyroCreationZ]

I agree with a_bab.
It's most likely the mill you're using (if you're using one!?)
Not to brag but I have a pretty good (homemade) ballmill.
If I put my meal in it and let it mill for only 10 minutes I get a very descent, fast burning meal. However, mostly I mill it for half an hour.
The burning speed is then superb.
So I'd say try to get a better mill, make sure your meal / BP is very fine particles and then make granules.
I bet you'll get much better results.
Good luck.

[blasterbert]

I agree with a_bab.
It's most likely the mill you're using (if you're using one!?)
Not to brag but I have a pretty good (homemade) ballmill.
If I put my meal in it and let it mill for only 10 minutes I get a very descent, fast burning meal. However, mostly I mill it for half an hour.
The burning speed is then superb.
So I'd say try to get a better mill, make sure your meal / BP is very fine particles and then make granules.
I bet you'll get much better results.
Good luck.

i find 27.2 grammes of 2fa gets a 3"shell to a nice height and 36.7 for a cyl shell.