M700 AICS fps questions

[SBranson23]

Well I finally got my chrono and have some odd results.

-Tanaka M700 AICS. (non-PCS version. damn)
-mags have G&G Gas Route Connecter Spring and G&G Power Pack
-DB Custom 6.01 tightbore
-Forse enhanced nozzle

With green gas results seem typical to what I would expect with .2g at room temperature being up around 580fps with a high of 600fps. Way too hot for the field. (looking for 500ish)

So I try super duster, the tetrafluoroethane134 variety and I only hit about 350fps with some crazy wierd shots down in the 280fps (or less!!) range. Not what I expected or hoped for.

What the hell?... Could it be the tightbore causing suck back because the 134 can't get the bb out fast enough? Or am I just wrong and this is what I should expect.

Right now the only solution I can imagine is to machine a new nozzle with some restriction in it and try green gas again.

The rifle is useless as it is now so any help would be appreciated.

[Skruface]

Originally Posted by SBranson23

What the hell?... Could it be the tightbore causing suck back because the 134 can't get the bb out fast enough?

That's not the problem - there is no piston to cause "suck back" like in a extra-long barreled AEG. The only [roblem I could see relating to the barrel (other than it being dirty or damaaged) is that you have insane reaction time and motor skills and are cocking the gun so fast that the bb is still in the barrel when you cock the bolt for the second shot (thus opening your pressurized tube at both ends), but I doubt that. Try using half and half (duster and propane).

Another issue might be that the valve spring is too stiff, and isn't open long enough to allow a sufficient volume of duster through, which has a MUCH lower pressure than Propane.

What's your velocity with the stock barrel (assuming you have it)? Have you done any testing with a stock magazine?

[SBranson23]

Originally Posted by Skruface

Another issue might be that the valve spring is too stiff, and isn't open long enough to allow a sufficient volume of duster through, which has a MUCH lower pressure than Propane.

That's what I was thinking too. I thought of trying to modify the rocker arm slightly so it depresses the valve just a little more. I also just machined an inner limiter for the nozzle so I will try that first.

I'd rather not go back to the stock barrel and revert the mags back to stock but if this limiter doesn't work I will.

As far as mixing gas, I tried filling the mags with duster then tried to put a fart of Green gas on top (I figured the higher pressure would add just a bit) but the result was a horrible drop in FPS down to the mid to low 200's.

Go figure that...

[ILLusion]

How did you remove your nozzle?

[SBranson23]

The first one, the original, I removed with some vise grips
I picked up two of the Forse nozzles and have modded the second. I still haven't gotten around to removing the one that's in there yet but I suspect it won't be as messy as the first time.
(having some pistol problems at the moment.)

[ILLusion]

So you basically just yank the nozzle out?

[SBranson23]

Yeah, you bascially have to yank it out. You could probably do it without mangling it so badly but I figured it was destined for the trash anyway.
The new one is just held in with a thin film of super glue so hopefully I won't wreck it when I try to remove it.

[Spitfire]

get a powerbolt ;-)

[LyquidFyre]

You could always try a differential metal expansion trick.....if they're differing metals

YOu know, just hit one with some hot water and then the other with a good upside down spray of duster. Who cares if you might crack stuff in the process

[SBranson23]

The problem with the power bolt (as told to me by a friend with one) is that the nozzle is integrated and quite short. The replacement nozzles that are longer seat the BB in the chamber better with more consistency and thus producing more accurate results.

I had success last night! I picked up some brass tubing from a local RC/Hobby shop. The lengths are sold such that the inner diameter of one is the almost exactly the outer diameter of the next smaller size. So I got a few lengths of different sizes. The first one took about 1 1/2 hours of patient sanding, filing, polishing to get it to slide inside the nozzle opening. Chrono'ed that and still too hot, mid 550's with a few up higher. So I drop in the next tube, reducing the nozzle opening size just a little and presto. After the first shot (which is always low) it seemed to settle around 510fps. Pretty hot weather these days so I am confident this will be about exactly right. If not I can always thread the next sleeve in reduce the fps further.
Neat system.

[Skruface]

Sounds like success. You should document this, with tubing sizes and measurements, for other non-PCS TANAKA owners.

[Spitfire]

hehe fortunately i have the pcs still on.. from 380-850 fps... all possible :-D

[SBranson23]

I'd love to see a photo of the PCS system. I wonder if the non-PCS could be modified.

[B.C.Hawk]

Are these clear enough? These are just some quick shots.

[Styrak]

Holy blurry! Put on macro mode man!