Dynatec, Dynatex, VTG, BFG - how it works and take down

[amateurstuntman]

So, the Dynatec grenade.

 

It has been my trusty companion for many years now, I forget how many.

 

I bought mine direct from HFM Pyrotechnics many many years ago, could be more than 10 years - probably is.

 

I have seen it referred to as a delay type BFG (Blank Firing Grenade) which I suppose it is and a Dynatex grenade too.

As Zero-one had it in stock as a Dynatex I am inclined to believe it is actually called a Dynatec.

 

To be honest I can't remember what it was called when I bought it.

 

Recently SWAT Tactical has released the VTG or Versatile Training Grenade which is (as far as I can tell) exactly the same thing in a different casing.

They advertise spares and repair for the older grenades and when refining their product for release they said they were trying to get the internal dimensions of the casing correct for a 4 second delay - that implies they were trying to make their grenade work with a shuttle with the same dimensions as the previous model.

 

Anyway, none of that matters - what matters is that (in my opinion) the Dynatec is the best reusable bang available anywhere.

 

Here is how it works.

 

Inside there is a shuttle with an o-ring round it and a metal pin on the top.

When you cock it you push the shuttle down - against a spring, through an area where the o-ring does not touch the sides of the casing and into an area where it does.

Once the shuttle enters that area the o-ring forms an air-tight seal and usually you wouldn't be able to push it all the way.

 

The shuttle contains a tiny air bleed valve that lets it go all the way down though.

 

Once it is all the way down a cam holds the shuttle in place and the spoon holds the cam in place.

 

When fired the cam is released and the spring pushes the shuttle up, because the shuttle's o-ring is sealed against the sides of the shell a vacuum is formed and the shuttle can only move very slowly as the air very slowly gets through the bleed valve.

 

Once enough air has got by the bleed valve the shuttle enters the part of the body where the o-ring does not touch the side.

 

All of a sudden there is no vacuum and the shuttle shoots up to the top of the case where the pin on the shuttle hits the blank and you get your bang.

 

 

Enough wall of text, on to the pictures.

 

Here is a picture of a Dynatec dismantled, it is a very early one:

 

Here is a drawing of one showing it in a pre-fired state and while firing:

 

I hope that makes sense.

 

 

 

To pull one apart.

 

With SWAT now selling spares you may want to pull your grenade apart - here's how (if you are ham-fisted and mess it up it's on you, OK?).

 

First you need to cock the thing, don't do it uncocked - things could go *poing*.

 

Then, put the grenade upside-down in some hot water until it is pretty hot, this softens up the plastic and will reduce the chances of the case splitting or cracking.

 

Once out of the water, dry it off and put something sturdy though the blast holes in the cap:

 

 

 

Then you need to firmly lever up on the sturdy thing you have placed in the holes.

 

The top will just pop off.

 

 

On close inspection you will see that the top has a protrusion that fits into a groove in the casing.

 

 

 

 

Once that is out you can place something into the grenade body to push down on the shuttle and then pull the pin.

Very slowly let the shuttle up, when it hits the part of the casing that is wider is will jolt, be ready for it.

 

Once the shuttle is out it will look like this:

 

 

Here is the hole through which the vented air moves:

 

 

Here is the bleed valve right up in the body of the shuttle:

 

 

 

 

Once that bit is out you can see into (and clean) the casing of the grenade:

 

 

 

You can tap out the pin holding the spoon:

 

 

And you will be left with a totally stripped grenade:

 

 

 

Re-assembly is the opposite, put the shuttle back in, cock it and then put the top back on (warming the plastic).

I close it in a vice to ensure even pressure.

 

 

Hope that helps.

[RSM]

Nice guide, I think I've seen the cut away diagram before....is it possible to adjust the jet at all to increase the time taken for thing to go off?

[TheEgo]

Supposedly yes the original BFG's are adjustable. No idea about the VTG copies!

[amateurstuntman]

If you want it to take longer to go off you can leave it cocked for ages.

It takes some of the tension out of the spring.

A tighter o-ring might do that too.

 

The speed of the shuttle is set by the size of the hole in the brass plug. The hole is tiny, I'm not sure how one would go about adjusting it.

I'll try a few things.

 

 

 

[farrasdevell]

I love you, i have been needing to do this for sooo long one of my bfg's striker pins has become rounded and unreliable ow i can get in there and replace it

[hotelkilo]

nice article and pics, im sure i recognise some of those images..

 

btw it is  'DYNATEX'  i have an original box from a long long time ago. 

 

the original inventor sold these in gunmart as long as 20 years ago (for £35 each !!)

 

he had invested a lot of ££ in having all the poly bodies made up in 1 big batch and was hoping to see a return on his investment,

 

after a few years of lack lustre sales to re-enactors (this was just as airsofting was taking off here as a pastime) he sold everything he had left to HFM pyrotechnincs and moved onto other projects, like the impact grenade.

 

so HFM took over the uk based sales of these items, putting the price per unit up AND putting the 'bone-fide use' restriction on them, (that never existed legally afaik)

 

ill see if i can get a pic of the original box and of an old gunmart ad

[hotelkilo]

here is a scan from page 122 of sept 1996 Gunmart

 

 

(removed contact details) 

[thatguy404]

Thanks Stunt for all that handy information!
Pretty sure I have spare o-rings for these.
Joys of working in the motortrade

[Sidewinder-forge]

Excellent info, now what about the impact one?

 

SAS

[gisburn20]

Beautiful work Stunt, 

 

Now, who is going to start building these for us at a bargain price in their garage?

 

The Impact version was supposed to be easier and cheaper to manufacture due to the lack of a timing device,

 

yet they are more expensive than the originals.

 

I'd love a pair of the impact version but the price point is beyond me currently.

 

end rant.

 

Good work Stunt!

 

Jim

[Apex]

This is it now, we are all getting shafted on the price for these :<

[amateurstuntman]

I never understood why these were never cloned.

 

I mean, there are only 6 major parts.

 

For low volume runs, you could machine the body out of ally.

 

I would make the top solid with just a firing hole and have the bottom screw off for maintenance.

You could do a variable delay one with a carburettor style adjustable needle perhaps.

 

I would love to meet John Ellis, these are so simple yet so reliable and tough - he is clearly a genius.

 

 

 

I could do a take down of an impact BFG but I don't have one.

All it probably has is a knife-edge sear inside it.

[TheEgo]

There are 2 types of impacts about from dynatex.

They cheaper poly/alu body version

The steel body. Which were restricted sales to Police etc.. (not a legal restriction)

 

I have the steel bodied version. I believe they operate in the same way. Although the steel bodied variant is more reliable (quite a few reports of the poly/alu version misfiring/not firing)

 

Impacts don't have a sear as it's not a breaking action that drives the pin out and it doesn't need to be reset. It's a sprung loaded counter weight. More than likely against a concave/convex surface.

[amateurstuntman]

So it's just a weight on a pin?

 

That means it would only go off if it landed pin side down right?

 

 

Seems a bit silly.

It would be much more complicated but one that fires due to an impact on any side can't be that hard to make....

[thatguy404]

Didn't SWAT BFG, claim their M84X device to be more reliable drop end on end?

http://www.blankfiringgrenade.co.uk/shop/category_8/bfgx-m84x-training-device.html?sessid=b8OjA638Ht8AdsFIUHUmkIQdqjYCLw3JAoHPgHcsP12CPqLdAnES6gFisgeXHkvV&shop_param=cid%3D%26

[amateurstuntman]

Yeah, they say it'll go off on either end, what if it lands on its side?

[thatguy404]

Which is what holds back my purchase...

first and only don't allow the use of the vtg yet, so what's the deal with no current alternative apart from someone's ancient abused overpriced bfg.

[DrAlexanderTobacco]

Which is what holds back my purchase...

first and only don't allow the use of the vtg yet, so what's the deal with no current alternative apart from someone's ancient abused overpriced bfg.

Really? I spoke to one of the marshalls at F&O The Mall and they said I could use one no problem.

[thatguy404]

Maybe miscommunication then.

vtg ahoy I suppose

[TheEgo]

Yeah, they say it'll go off on either end, what if it lands on its side?

 

 

The Dynatex Steel bodied impact grenades function regardless of orientation.

It's sprung loaded counter weighted. If the top toggle part moves off it's axis in any orientation with sufficient force the pin is driven out.

It might not be clear the function from my explanation but they work incredible reliably.

 

This is not the case for the Alu/Poly bodied version which I believe suffer from "non firing" due to how they land. I'm also led to believe that the SWAT M84 and M84X also suffer from this. Although this is only from observation on the demo videos as it seemed sensitive to which way it was thrown/dropped.

[LordElpus]

F&O Midlands and North are not allowing this at the moment.

[amateurstuntman]

The issue is (I believe) their insurance carrier.

Their policy specifically names Dynatex grenades, they will add the VTG but they need some documentation from the manufacturer which has not yet been supplied.

That's what I understand, I could be wrong.

[Sidewinder-forge]

How does it self reset though?

 

SAS

[TheEgo]

How does it self reset though?

 

SAS

 

The Dynatex Impacts?

 

 

The counter weight is sprung loaded, (So in a stationary position the spring puts the firing pin in a retracted position)

[Apex]

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