FPS fail

[HuntR]

Right so here goes. I have a dboys M4 as a backup rifle, and it had a leaky air nozzle. So i replaced it with a guarder air seal nozzle and a guarder double o-ring cylinder head. Now the air seal is very good. So i put on a Guarder SP90 spring also. Now my issue is it's getting about 260-280 fps. Is that right for that spring. I was under the impression that a Guarder sp90 should have gotten me close to the 330 mark. The rest of the gearbox is standard.

[guard-sniper87]

Re: FPS fail

No the sp90 will give less then the 310

best to check your hop rubber or airseal on the hop unit see if it is damaged

[HuntR]

Re: FPS fail

Hmm i must have read things wrong. I've checked the seal on the hopup all seems fine. Right i'm going to put an sp 110 now to see if it is ineed my chrono. I'll report back when iv'e done it.

[guard-sniper87]

Re: FPS fail

The 110 spring should give you around 360 mate

[paulyboy]

Re: FPS fail

I recomend a m100 mate as you said you have re done all the air seals so would say it will be runnin 330 ish to 340 ish

[HuntR]

Re: FPS fail

spring is guarder. Tighter coils on the spring guide right

[guard-sniper87]

Re: FPS fail

Yeah tighter ones over spring guide

check the hop rubber mate and also see if the piston head o ring is ok

[HuntR]

Re: FPS fail

Cheers Guard it was indeed the spring. Put the SP110 in there and it's doing 310-320 with .25's. Ran out of .2's to chrono. So it's about 350-360 with .2's After the spring is bedded in it should work nicely.

[guard-sniper87]

Re: FPS fail

Glad to help mate

Enjoy

[gijohn2]

Re: FPS fail

I recomend a m100 mate as you said you have re done all the air seals so would say it will be runnin 330 ish to 340 ish

Not allways.
My friends guarder m100 kicks out 360 FPS.

[sj_asc]

Re: FPS fail

Guarders always shoot hot, the SP90 i fitted in a team mates TM g36c is still getting high 330s. All SP110s i have fitted hit a nack above 400 from fresh and settle to just below. I would check the air seals and are you matching the cylinder to the barrel length>?

[Gaffa]

Re: FPS fail

Have you been doing your testing with the hop turned off?

My AUG lost 20fps - 25fps simply because I tuned the hop to get the best range.

Also, if you're still having problems, check the piston head. Can you push the piston (with head of course) into the cylinder all the way whilst keeping your finger over the air seal nozzle?

[HuntR]

Re: FPS fail

As i said guys all the seals are excellent. You can't push the piston into the cylinder with your finger over the end no. No matter how much pressure you put into it. With the finger off the nozzle it goes nice and easy. Piston head o-ring is in good condition. What it doesn't have is a bearing spring guide, or bearing piston head. So that will reduce the fps abit as far as i'm aware.

Cylinder to barrel length is not matched no. It's the stock cylinder that came with the gun, which is a non ported cylinder. All old dboys come with these. Barrel length it 363mm by the way.

However this is my dmr project, so i will be getting a 509mm barrel for it when my new front end comes.

Hop is what i believe to be all the way off. All the way to the left on the unit, so yes all the way off

[richardy]

Re: FPS fail

well there you go, switch to a full cylinder theres another 10 - 20 fps, give that a go

failing that theres millions of other points of air loss its just being anal or fastidious enough to track them down, i had an m14 the other day with unknown air loss, it was the return spring on the tappet plate. it just wasnt returning it fast enough. fit a spacer in behind the spring in the tappet plate spring channel and increased the fps from 250 - 350 with an m100. 100 fps air loss from a crappy spring which wasnt working properly..

just an example ..

[HuntR]

Re: FPS fail

It is a full cylinder mate, hence non ported. But the fps is fine as is now. Any more and i wouldn't be able to use it at my site. When it's short stroked by 3 teeth it should fall nicely into the 330 range. Sites fps is 350 max on all guns. It's just a backup gun for when my main decides to splodge itself. But it would still be nice for it to actually reach someone.

Basicly when i got it it was 270 fps, so i changed the barrel to a tightbore. Fps went down to around 50 and i couldn't figure out why. So i stripped it, and found the air nozzle to be utter shite. Upon further inspection, the dramatic fps loss was due to the barrel. The guy i got it off hadn't ever cleaned it. It was so thick with crap it took me a good hour to clean it thoroughly.

Fps then went back up to 270-280. So today my air nozzle and cylinder head arrived, now me being a total newbie with internal work, got a new spring too. So i don't know what the fps with the old spring was.

I was however under the impression that the Guarder sp90 would have gotten me closer to the 1 joule mark. Now my pinion head on the motor comes off by itself. So i don't know if that could be the cause. Perhaps when it gets put under stress from the spring it spins the opposite way so the piston isn't making a full cycle.

I've not heared of the above happening before, but it does sound logical to me. And i can't put my other motor in there as it's a systema turbo. And with a pretty much stock dboys i just don't want to risk it to see if that is the issue.

I am now getting it seen too, and having some upgrades installed and some mods doing to it. Like AOE for instance and short stroking. I have an element max speed motor on route for it, along with prometheus metal bushings and a bearing spring guide. I only plan to run it on a 9.6v battery. I do have a mosfet for it too, as it's going to be my DMR.

Now i know someone's bound to say why are you short stroking a DMR, and my answer to that is...

As my site limit is only 350, i want a very fast trigger response, without having to switch to a lipo battery.