Consistency at High Speeds

[pestobanana]

Hey

So I've been working on my M14 to try and get a faster trigger response, but at high rates of fire the FPS is extremely inconsistent. When it's set at 31 rps, even on semi-auto fps fluctuates from about 350-455, and even a few oddballs at 250. When the rate of fire is set lower to around 18, the fps is a consistent 455. Feeding is fine at any speed, but how do you guys get consistent FPS at high speeds?

[ThunderCactus]

works fine at slow ROF but not at high ROF.
So break it down, what's changing?
piston releases at the exact same speed
if it were pre-engaging, it would be stripping
really the biggest difference is the tappet plate needs to move faster, so it's likely just not getting back to the forward position fast enough.
Push the air nozzle back with your finger to test for resistance, if you need to, increase the tension on the tappet plate spring, or shave down one side a little bit (like .1 or .2mm), and lightly grease it and the ways.

[Hectic]

Are you trying to build high speed or is it just trigger response you want?
If its just trigger response try a merf3.2
You can buil a higher speed setup then turn the rof down.
What then happens is the first shot the box cycles full speed then it meters itself down to the rof you set.

[ThunderCactus]

His problem is that he's having inconsistent fps on semi-auto
So having semi at full speed and slower full auto wouldn't fix the problem
Being able to lower the overall ROF slightly might help though

[Hectic]

Yeah i was kind of thinking its one of two things. Either the hop up cant return to the nozzle fast enough (thats assuming it like an m4 hop up in the sense that it moves back n forth as i dont know about m14 hops)
Or that the nozzle isnt seating into the hop up either because its getting pulled back by the tappet too quickly or tue tappet to sector interface is off a lil on the high speed setup or the return spring isnt pulling forward fast or hard enough.
Tho rereading the post now that im fully awake it seems the only change being made is ramping up the rof and that leaves me confuzzled as if it works consistantly on lowwer speeds it should in theory work fine on higher speeds.
Unless the myth of suckback is presant and at the higher speed the piston is starting its rearward cycle befor the bb has left the barrel.
Wonder what barrel cylender combo is in this thing?.
Also perhaps the cylender head oring is just inconsistant in expanding/contracting when its tryin to do it rappidly?
Dunno kinda stumped based on the fact it performs normaly at lowwer speeds.

[ThunderCactus]

not sure what you mean by the first one
it's most likely the nozzle isn't coming back forward fast enough
just because a gun works fine at 800rpm absolutely does not mean it will work at any rof above that
suckback is not physically possible unless you have a seriously low fps, and unvented piston head, and it's typically not an erractic problem, it would be very consistent.
the piston head O-ring is fine, because the piston is always being released and moving forward at the exact same speed, there's no reason it should be failing to compress at higher ROF

either something is slowing the tappet plate down, lack of grease, rough edges, sector gear shimming, or maybe it needs a more RIGID tappet plate.
I've seen issues at higher ROF where the tappet plate bending too much caused feeding issues, could be a similar problem for fps.

[pestobanana]

It is definitely not pre engaging, the piston is still in good condition.
Suckback is not possible, because as dumb as the theory is, it wouldn't apply in semi auto.

I've already short stroked the tappet plate and put in a stronger tappet spring, I guess I'll take the thing apart again and shave more material off, modify my sector delay chip to release earlier and regrease.

I guess if I can't get it to work I'll have to use my MERF's rof control

[lurkingknight]

you'll need a sector clip, stronger tappet spring and you'll need to get into the rails the tappet slides in and polish them with super fine sandpaper. Also polish your tappet plate where it interacts with the rails. Sand the front face of it as well, try go get it to sit farther forward.

You could also have poor air seal at higher speeds from bad sealing components like the o-rings. Sometimes they make a difference.

I have a feeling though this is more to do with the hopup not being stabilized to the front of the gearbox or the tappet isn't returning forward fast enough.


also... at that fps are you using a soft rubber or hard rubber?

[pestobanana]

Originally Posted by lurkingknight

you'll need a sector clip, stronger tappet spring and you'll need to get into the rails the tappet slides in and polish them with super fine sandpaper. Also polish your tappet plate where it interacts with the rails. Sand the front face of it as well, try go get it to sit farther forward.

You could also have poor air seal at higher speeds from bad sealing components like the o-rings. Sometimes they make a difference.

I have a feeling though this is more to do with the hopup not being stabilized to the front of the gearbox or the tappet isn't returning forward fast enough.

also... at that fps are you using a soft rubber or hard rubber?

I already have a sector clip, but feeding is not an issue so I'm going to remove it or modify it to release earlier. I'm using the strongest spring I can find (came off a G&G), I don't know where to find tappet springs for a CA/G&G M14. Front of tappet plate has already been sanded, I'll try sanding more off the front and sides though.

One good thing about this gearbox design, is that the hop up unit is literally screwed on to the gearbox, and I have o-rings on the barrel that really push the unit tightly against the gearbox.

I'm running a modify moundless rubber, not sure if it's considered hard or soft.

[lurkingknight]

yeah, the hopup is mated to the gearbox on g&g/ca m14s.. it's a nice feature.

Only issue is if the CA is like my g&g, the tappet spring is a compression spring not an extension so you can't just clip loops off. You'll probably have to take measurements and go through mcmastercarr or fasental to find a stronger spring.

[pestobanana]

Problem resolved

It turns out the problem was that the sector gear clip was causing pre-engagement of the tappet plate, which is why my fps was extremely inconsistent. Fortunately the gun still feeds reliably without the clip, even though I short stroked the tappet plate thinking it was moving too slowly.

[ThunderCactus]

Does anyone remember when sector clips didn't exist and we were still doing 1500rpm? lol
Should only use a clip if you're already having feeding issues, not if you're anticipating feeding issues.

[Azathoth]

Originally Posted by ThunderCactus

Does anyone remember when sector clips didn't exist and we were still doing 1500rpm? lol
Should only use a clip if you're already having feeding issues, not if you're anticipating feeding issues.

What are you talking about? People have been sanding nylon bushings and turning them into DIY sector clips for YEARS.

[ThunderCactus]

They weren't commercially available.