VSR 10 very low fps?

[-Dan-]

hello all

i upgraded my vsr-10 with all the necessary parts to run a 150% 170% spring.

i wanted to see what fps it was shooting with the 170% spring. i was expecting some were between 500-600 fps with 0.2

what i got was 410 fps.

what would be causing it to be so low?

the only thing i can think of is the o-ring around the new piston head was very loose, is this normal?

any help please.

ta

[leiwin]

what spring did you use a 170 systema spring ?
or was it another Brand there are different ratings by maunfaturer from what i understand
did you upgrade the barrel or hop up at all if so make sure the seal is in there correctly
the o ring is free floating on the stock cylinder head but im not sure with upgraded ones ...

[-Dan-]

sorry it was a laylax spring.

[BBS]

you probably did something wrong upon re-assembly of the gun. try using teflon tape to tape any parts where air would pass through and make it airtight.

[-Dan-]

i have put a tightbore barrel in, but the hop unit is stock.

[bean]

Ok do you have the o-ring that came with the original piston? If so use that one over the one that comes with the silent piston. Also does your piston have a huge hole in the center of it? If so its missing the silent shaft or grub screw. If it has a white shaft that is how your losing a lot of speed. It plugs up the cylinder head for the last bit of the pistons travel. This creates a pocket of air to slow the piston down and make it "silent". If you have the grub screw thread lock it and replace the white shaft with that. If you don't you can cut the shaft down. Make sure the threads between the cylinder head and cylinder are teflon taped. Once you do this take the trigger/cylinder group. Cock the gun and put your finger over the hole in the cylinder head. If the piston inside doesn't move you have a good seal but if it comes in contact with the front of the cylinder head without you removing your fingers the seal is bad. Try that out and get back to me. Taking apart the hopup unit and teflon taping it is also a good idea.

[-Dan-]

bean to the rescue again.

i dont have any oringinal parts, how ever the piston head does have the white shaft on it. i just cut this down flush with the piston head?

i will also put teflon tape around the cylinder head and hop unit.

do u mean put my finder over the hole when cocking the gun, or when firing the gun?

cheers

[bean]

cock the gun then put it over the hole. Your looking for an air leak within the piston group. Yes cut the shaft down so its flush. Its rather useless. It causes fps inconsistency's and drops the speed a whole lot.

[-Dan-]

ok, cheers for your help as always bean. i'll do the mods and report back when there done.

[tsuru]

Some pistons (don't ask me which ones right now, all I know is that they exist) will fail the piston compression test that Bean outlines even though they have normal compression. With a 150 or 170 spring I too would chop the airbrake (white shaft sticking out of the piston) as this could account for your entire FPS discrepancy and it's not going to make your gun any quieter at the FPS it should be shooting at.

[-Dan-]

Cheers for all your help guys.

i have finished all the mods, taking some pics along the way. if you could have a quick look and see if what i have done is correct that would be great.
unfortunately i will not be able to chrono the gun untill the 27th. but at the moment it seems to be firing fine.

one thing i was concerned about, and you can see in the pictures is how bent the spring is. Is it normal for the spring to become twisted and bent like this? and will it cause any problems?

pics

http://img172.imageshack.us/img172/5049/dsc01462fp3.jpg

http://img523.imageshack.us/img523/8357/dsc01457oz3.jpg

http://img376.imageshack.us/img376/7030/dsc01459tt2.jpg

http://img408.imageshack.us/img408/4336/dsc01472xj9.jpg

http://img365.imageshack.us/img365/6628/dsc01478vv7.jpg

http://img458.imageshack.us/img458/5708/dsc01479rf0.jpg

http://img470.imageshack.us/img470/1263/dsc01482if1.jpg

[bean]

Looks good man. I hope it works good for you. The spring is bent like that because its quite a bit longer then the actual cylinder. When it is stuffed inside it can only compress so much without anything holding it in a straight line. So in other words its fine. It should be firing a lot better. Get a cylinder head pro or if you know someone who is competent in metal work get them to widen the inside of the nozzle on the cylinder. It will allow for better airflow and a better fps. With the larger spring it can be trying to force the air out so fast that its creating a pocket of air because it cant push it out fast enough. If far to lazy to crap my fluid mechanics book and do the work to figure it out so those are just my suggestions.

[CDN_Stalker]

Originally Posted by bean

cock the gun then put it over the hole. Your looking for an air leak within the piston group. Yes cut the shaft down so its flush. Its rather useless. It causes fps inconsistency's and drops the speed a whole lot.

Ditto, that's the brake, it cuases a lot of problems with upgraded VSRs, low velocity and such. Slice it flush, you are good to go.

[-Dan-]

Holy crap!!!

just had the chance to shoot a few rounds. the difference is amazing. think i'll have to drop the 150% spring back in tho, as this thing is kicking out some serious FPS. way to much for skirmishing. very good for plinking tho.

thanks again for all your help guys.
Dan