NBB Five Seven

[Stealthbomber]

Just daydreaming about this...

 

I was wondering about building an NBB version of the TM 5-7 for all the sneaky-beaky Sam Fisher stuff I currently have a Mk23 for.

 

Just looking for any advice or suggestions for this.

 

For starters, IF the gun had a double action trigger, basically all I'd need to do would be to fit something to the trigger which'd push the GBB chamber back and then allow it to spring forward again(so a BB could be loaded) before the gun actually fired.

This I could probably manage but, given that the Marui 5-7 has a single action trigger, it doesn't actually help me much.

 

Soooo....

 

I think I need a more radical solution... which I have no idea about as yet.

 

Thing is, the bottom line is that it will HAVE to work off GBB mags so it WILL have to have a GBB unit that moves backward and forward (with the trigger, most likely) to scoop a BB out of the mag and poke it into the barrel before firing.

 

Other than that, I have no real idea where to start.

 

Anybody know of a cheap NBB with a DA trigger that I could, perhaps, buy and cannibalise for parts?

 

Ideally, to save a few bob, I'd like to not have to buy a complete Marui 5-7 and then chop it up (probably cos I'd never do it) so I'd like to, instead, buy an NBB of some kind and then a Guarder 5-7 kit and mash them all together.

 

Suggestions?

[renegadecow]

This is about as cheap as it gets.

http://www.rsov.com/index.php?target=products&product_id=6364

 

You might have some luck in making the trigger and hammer a DA jobbie because the trigger pull itself is fairly long. The problem ensues with the hammer and loading mechanism. Wanting to keep the existing GBB mags would leave you with a design similar to Marui's Mk23 where it has a GBB looking nozzle but goes forward along with the trigger to load a bb. How about slapping the 5-7 shell around an NBB and call it a day? There's just far too many parts to fabricate if you want to keep the 5-7 mag.

edit:

Or why not have a whack at short stroking a 5-7? They're a great deal quieter because the slide doesn't move around as much and doesn't pick up as much inertia. Not as quiet as a Mk23, but could be done in say 30 minutes tops.

[Stealthbomber]

FWIW, the basic, blurry, plan (if you can call it that) that I currently have involves having a GBB chamber which is sprung so it's usually in the retracted position.

 

All I'd then need to do would be have a bar sticking up, vertically, from the trigger linkage which'd push the GBB unit forward, pick up a BB and then seat fully forward just as the hammer released to fire the gun.

You then release the trigger, the GBB unit retracts and it's ready to fire another shot.

 

Thinking about it, I guess the hammer assembly is gonna be the big issue.

It'd need to be compatible enough with the 5-7 to fit in the frame and work the mag but also be double-action.

Bugger.

[AnotherJesus]

Interesting idea. I'd given some thought before to making my spare ARMY Detonics Combat Master into an NBB type gun. The way I thought about it was to stop the gas from pushing the slide back during firing. I wondered if you removed the valve from insdie the blowback chamber, would all the gas choose the easier option of escape and go out the front of the gun? Or would it just lead to most of the gas going out the front, and the slide still moving an annoyingly small amount. If that's the case, to stop the silde from moving at all would be difficult. You might get away with it if you just whacked in a great big recoil spring, and a metal slide.

 

So, if the slide doesn't move, you're going to need some way to reset the mag valve. This could potentially be done by removing the part that locks the valve knocker forward. I'm not sure of the design on a 5-7, but I'm sure I found a way to do it on a 1911. This in turn, might just decrease the amount of gas you're letting out of the mag, and end up with BBs trickeling out of the barrel. So you could whap in a bigger hammer spring, and hopefully that would somewhat compensate for it. The bigger hammer spring would in turn increase resistence on the blowback mechanism, slowing the slide down even farther.

 

If this all worked of course, you'd end up with a single action GBB. So one shot, cock it, and fire it again. Which if you were to do, would be the equivilent of how some RS firearms work with low velocity amunition anyway. I think M14s work like this on subsonic ammo, and if Metal Gear Solid 2 is anything to go by, so do m9s when they're useing tranquilizer darts .

 

Might be doable that way, but you're effectively just increasing resistence untill the system stops working, and there's something that sounds bad about that idea to me. Also, if you modify anything, and it turns out it didn't work, you're left with a borked gun.

[renegadecow]

Want for a single action, single shot from a GBB, you can simply remove the floating valve entirely and plug up the rear either by physically blocking it with some kind of material, or you replace the nozzle return spring with a stiff rod so it prevents it from moving. Then you remove the part that holds the valve stopper so all the gas doesn't go out in one go.

Next, if you were using a WA magna system, this is all you need to do. But on Marui, the hammer still imparts pressure on the valve knocker until it's reset by the slide. You need to modify the MSH so that the hammer only provides tension up to a certain point and stop so that the valve knocker can reset itself. You need to get at your MSH and remove the retaining pin at the side. A new hole situated lower (requires some calculation) has to be drilled out for the pin to be relocated. Alternatively, the hammer strut itself can be shortened so that it does not engage the hammer spring after a certain point.

edit:

forgot we're talking about a 5-7 here and not a 1911

[Stealthbomber]

Well, a while back I tried turning my KSC Mk23 into an NBB simply by removing the shuttle valve inside the GBB chamber and then replacing the little springs fitted to the blowback unit with lengths of brass rod.

 

All worked relatively well but it DID make it clear that having a gun that needs to have the slide manually cycled prior to shooting is not ideal.

 

As I say, I think I could get around that in a similar manner that Marui do it on the Mk23.

The standard GBB chamber could be used, which'd be handy cos it does the job of loading the BB and channeling gas out of the mag and into the barrel, but be controlled by a vertical bar sticking up from the trigger bar to pull it forward into position prior to firing.

 

If the 5-7 had a DA hammer we'd be 95% of the way there but, alas, cos it's SA only I'd need to come up with a whole new way of getting the gun to fire.

 

As for resetting the mag, what I really need is a system a bit like the KSC Mk23, where the hammer hits the striker and then immediately bounces backward again.

That'd just release a small amount of gas and then (hopefully) let the valve close again.