Incredibly low FPS. rounds only flying about 10 feet.

[DA8GizMo]

Hi all.
As above, I took my rifle to a skirmish yesterday and at chrono, to my horror, the bbs were only flying about 10 feet from the barrel.
All the work that's been done on this has been by myself and I'm fairly confident on stripping a gearbox and putting it all back together again.

G&P Magpul Sentry
Guarder M110 Spring
Madbull Ultimate Hop
Madbull Black Python 6.03 Barrel
Shooting at a consistent 350fps with 0.25s

Now I've never had any problems with this but I thought the gearbox was just a touch on the noisy side so I decided to re-shim the gears.
Plus I fancied a few other upgrades so I picked up an Lonex Titan A2 Motor, Modify 8mm Ceramic Bearings and some 11.1v lipos

What I've done :

Swapped out the stock G&P High Speed motor for the A2 (which included swapping out the G&P screw in style motor connectors for some SRC Gold plated Spade connectors).
Swapped out the bearings for the Modify Ceramics
Did a full re-shim (pinion to bevel gear)
Whilst I had the gearbox open I also decided to short stroke the piston to see how much of a difference to the fps and rof it would make.
I removed the last tooth from the piston and the last tooth from the sector gear.

put everything back together and dry fired to test everything was working.

Trigger response with the new motor and 11.1v lipos is much faster and nicer!
rof seems insane now too!
Smiles all round! (or so I thought)

Stupidly, I didn't put any actual rounds through it before going to skirmish. Silly me!

So now I'm at site, go to chrono and then disaster.
I leg it back to the safe zone and do the quickest gearbox strip known to man.
I figure that it's an air seal issue as the gears still all seem to be working and rounds are feeding and leaving the barrel.

I took the piston and cylinder out, placed my finger over the end and and pushed on the piston.
I seemed to get full air seal as I could only push the piston in a little ways before hitting resistance (due to my finger over the end)

My mate also runs a G&P Sentry so we decided to swap uppers (hop and barrels included) to see if it was a problem there.
His gun continued to fire just fine with my upper and mine still just dribbled out bbs with his.
So that, in my mind, rules out the hop chamber, hop rubber and barrel.

So I'm thinking that it must be an air seal problem in my gearbox, but as i said, i did test the seal with the piston and cylinder.

I'm not sure what else it could be or what to check.
Is it possible that short stroking one tooth from the piston and sector gear cause this?

Any advise or help would be greatly appreciated.

Thanks

Giz

[G33m4N]

Re: Incredibly low FPS. rounds only flying about 10 feet.

I'm not sure what else it could be or what to check.
Is it possible that short stroking one tooth from the piston and sector gear cause this?


Yes it could it the piston is not giving full compression, I would try it with a different piston and sector gear.

[Boo-Sabum Ben]

Re: Incredibly low FPS. rounds only flying about 10 feet.

Are you firing on semi only? Or full auto?

Did you have a look at the tappet plate and associated parts?

[rjb]

Re: Incredibly low FPS. rounds only flying about 10 feet.

Interesting problem...

You've done all the right things so far, so we know what its not, which is a good start. What would be useful info is the current FPS from the weekend's chrono if you can remember.

Two possibilities remain (assuming that the compression is OK - maybe be worth checking in non-safe zone conditions!)

Nozzle and general seal between gearbox and hop unit - Is the tappet plate seated correctly? Is the tappet plate spring correctly installed? How does the nozzle seat? Is it double feeding? All points made above by Boo

Gears and piston is the next possibility... Is the piston properly seated (i.e. on its rails)? How do the teeth look? Can you maybe post a picture of you handiwork?

Cheers

R

[dexadrine]

Re: Incredibly low FPS. rounds only flying about 10 feet.

Did you take the tooth off the pickup end of the sector gear?

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[G33m4N]

Re: Incredibly low FPS. rounds only flying about 10 feet.

Did you take the tooth off the pickup end of the sector gear?

Yer that's a good point.

[DA8GizMo]

Re: Incredibly low FPS. rounds only flying about 10 feet.

Hi all, thanks for the replies.
I'm at work at the mo but will post up some pics later on.

No, I removed teeth from the other end. The pick up end and AOE were still the same.

Sadly I didn't get to see what the chrono result was, the marshall just said " There's something drastically wrong here mate"
But like I said, it would only travel about 10 feet. I could flick a bb harder and faster with my finger!

As we were chrono-ing , we were only firing semi. Didn't try auto.
I had a quick look at the tappet plate but assumed it was fine as it was feeding rounds from the mag ok.
I'll check how it is all sitting and post pics later.

Thanks so far guys!

Giz

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[dexadrine]

Re: Incredibly low FPS. rounds only flying about 10 feet.

No, I removed teeth from the other end. The pick up end and AOE were still the same.

When short stroking you need to remove teeth from the pickup end of the sector gear, otherwise you will mess up the timing of the tappet plate/piston cycle. If this is the case it could well be part of the problem.

[DA8GizMo]

Re: Incredibly low FPS. rounds only flying about 10 feet.

Bugger. I thought you had to remove teeth from the same end..
So on the piston I removed the last tooth it catches before sending it home (i.e. the tooth nearest the piston head)
And then I did the same on the sector gear.
But should I have actually removed the first tooth from the Sector gear..?

Thanks

Giz

[dexadrine]

Re: Incredibly low FPS. rounds only flying about 10 feet.

You remove teeth from the pickup end of the sector and the release end of the piston rack (this is not essential, it does save some weight tho). Make sure your release tooth on the rack is metal.

[DA8GizMo]

Re: Incredibly low FPS. rounds only flying about 10 feet.

Ahh ok then. Well that explains is then!
So thankfully all I need now is a new sector gear!

Or would it make more sense to get a whole new gear set (so that they all match) ?

Thanks again!

[dexadrine]

Re: Incredibly low FPS. rounds only flying about 10 feet.

Given the price of a set of SHS gears, you may as well get a whole set.