Detonator Casings

EDIT: Double post, a moderator may delete this

[Edited on 24-9-2013 by Mathias94]

Quote: Originally posted by Mathias94

I don't know what your primary of choice is, but remember that mercury fulminate and probably a lot of other primaries is uncompatible with aluminium.

Blasting cap from paper

I just found a pile of discarded arrows at my gun club archery range. They were bent or fletchings were damaged and then discarded. You can also find these things on ebay as auction lots of either functional arrows or whatnot. You can find them at a price of $1 per shaft. The trick is choosing an elegant method of closing the bottom. As a way of keeping this post scientific (here's looking at you Bert )... +2 for brittle/high strength aluminum tubing. On the fracture toughness curve materials like this will absorb less energy during a charpy test demonstrating that less deformation energy is taken from the shock front... the material will deform elastically until the fracture point as opposed to a material that will transition past the elastic behavior into the plastic deformation zone and absorb energy inelastically. Though this shouldn't matter much if the quantity of primary is sufficient. And one last note, primaries don't really get characterized by critical diameter, but a composite cap with a boosting secondary should force you to compare this secondary critical diameter with the tube ID.

Quote: Originally posted by TGT

22 Magnum bullet casings I think would be perfect. You could heat them red hot and crash them in water or oil to make the metal more brittle, just a suggestion. TGT

Detonator Materials

Quote: Originally posted by Microtek

This is why caseless or semi caseless detonators are nice. If you use a cast energetic or a PBX for the base charge you can leave the end open, and therefore getting the most intimate contact possible between donor and receptor explosives.

True that, but cast base or pbx might be relatively hard to initiate, at least in the classical dimensions of an initiator charge. Depends of course what composition is used.
But perhaps the easiest way would be to leave the end of the base exposed....as in pressing the base charge into an open ended tube type containment. That way one can still retain structural integrity of the unit and have the added value of the exposed base charge tip. Just my 2 cents...

Quote: Originally posted by Microtek

You just have to have the lower part of the base charge cast (or bound). If you simply press the charge, you will lose too much structural stability. If you are worried about initiability, use something like nipolit (RDX bound in NC or NC/NG in a solvent casting process), a PETN analogue, PTX-II or you can use a small percentage of an inert binder such as a PU based epoxy. In a base charge there is no need for mouldability (indeed, in a semi-caseless or caseless design it would be counter-productive), so an appropriate glue can be used in amounts of just 2-5 % to make a hard PBX, which is easily initiated.

Yes, options are plentyful and limited mostly by the reach of our own imagination or lack of knowledge

Though I'm a bit worried about the critical diameter of PBX or melt cast bases with "classical" initiator dimensions (6-8mm). Depending on formulation this might become a limitation to success. Not saying that it will happen, just another aspect that must be accounted for when designing such a device. I've often ran into trouble when trying to initiate charges with limited dimensions and high density, either due to pressing, phlegmatisation additives or inert binders.

I have found the best option to be using basic plastic pen cases, the tubes can be cut to length, easily loaded and fused.

I have never had a failure in initiating a charge with these caps I made. People like to try and get clever and creative with detonators when I see no need to do so. There isn't much sense in using cast melt explosives or PBX's in the detonator itself. 500-1000mg of Pressed RDX, PETN etc. with 30-150mg of primary is all that's needed.

As seen here:




Here is a 17g TNT cast with the hole molded:



45g Picric Acid booster w/ same detonator:





A 60g ETN cast here detonated with the same detonator:



Decomposition of said ETN cast:






I've done quiet a few detonations but always stuck with the same style detonator, 700mg ETN and 200mg roughly SADS

Well, it depends on what your goal is....if you need a simple and working solution that does nothing more than fulfilling its function, then there is no need to get more clever about it

On the other hand one might feel the need to explore the effects of a more complicated and untried system. Who knows, perhaps we might stumble on something interesting in the process.....

Good to see you staying heart healthy by getting some cardio.

I don't want to get too far off topic, but I thought I would include the following jpg of a table taken from an old defense document (Powder and Explosives by A. G. Gorst). It provides some minimum mercury fulminate initiator charge weights for cast and pressed TNT and Picric Acid. As you know, granular TNT and picric acid are much easier to initiate than their cast forms. Very commonly, granular or crystalline TNT or picric acid was used as a booster to initiate cast TNT and cast picric acid.

BTW, did you check the melting point of your TNT? TNT even when of high purity is relatively insensitive to initiation.

TNT does take a bit of time to make, but after doing it a couple of times I find it fairly straightforward and with the right equipment (large flasks, etc) it could be made in large quantities relatively safely. It wouldn't take much longer to make a pound batch than it would to make a 15g batch.




[Edited on 20-12-2014 by Hennig Brand]

What is wrong about syringe casing?
I found some pics for this but it doesn't look nice
i personally shape it in a better way
is there anything attractive about metal casing?

Quote: Originally posted by ecos

What is wrong about syringe casing? I found some pics for this but it doesn't look nice i personally shape it in a better way is there anything attractive about metal casing?

An old photo:

4 mm dia Transparent straw casing, with direct contact HE plug, handpressed.

12% inert PETN PBX ribbon on 3 mm Al, covered in sand.

Quote: Originally posted by markx

Quote: Originally posted by ecos   What is wrong about syringe casing? I found some pics for this but it doesn't look nice i personally shape it in a better way is there anything attractive about metal casing? There is nothing intrinsically wrong with syringe casings...just one has to pick a suitable size and work out a neat and clean assembly and a "safe" process for it. For example insulin syringes would be of more appropriate dimesions. The ones on the picture are quite horrible and I would stay well away from using or handling such devices. If one can not spare the time and effort to perform clean and reproducible work, then researching the field of energetics is not a suitable passtime. Apart from unrivaled mechanical integrity in construction and handling there is not much more attractive in a metal confinement. In fact I would avoid it in amateur practice at all cost. The danger of shrapnel outweighs any possible advantages of metal casings for me. That's my personal opinion on the matter, but one has to make up its own mind about these choices.