intentionally mismatching barrel to cylinder to control fps?

[lurkingknight]

I have a p90 that I have 2 receivers for... I was wondering, could I change the ported cylinder to a non ported (or leave it alone for that matter) and change the barrel length to lower the fps depending on if I need the gun for indoors or outdoors? I could potentially put together a longer barrel with hopup and silencer to swap in and out depending on indoor or outoor play.

Now the question is... can I get enough of a difference in fps by mismatching barrels to cylinder?

I don't think I can drop 40-50 fps just with a barrel swap, but I'm curious.

[Ninja_En_Short]

Not only will you not lose enough FPS but you'll also lose accuracy dramatically.

[Azathoth]

Originally Posted by Ninja_En_Short

Not only will you not lose enough FPS but you'll also lose accuracy dramatically.

Not true

I run a non ported cylinder with a 247mm barrel the gun shoots a very consistent 423 and accuracy is not affected. If you require your gun to run ~400-435 their is no reason to run a non-ported cylinder. In my mind their is no reason to run a ported cylinder ever, anywas but that's another matter.

My suggestion is to buy a stock TM gearbox or a cheap JG one and downgrade it to 1j. Then treat the gun as a PTW with a more difficult cylinder swap. That would be the best way to handle your requirement of being able to go from field limits to CQB limits

If you own two P90 lower frames or bodies then I don't understand why you would even be asking this question as you would have 1 gun to pickup for the field and another for CQB.

[CDN_Stalker]

Cylinders are ported get the maximum BB velocity instantly in order to get them out of shorter barrels at the proper velocity. Put in a full cylinder, the maximum velocity is gradually acheived during the piston stroke, which is fine for longer barreled guns but brutal for shorter barreled guns. I tried a full cylinder in my MP5 w/330mm barrel one day, lost 30fps instantly.

[m102404]

Don't know about the P90....but I did that with M4's.

SIG length inner barrel....resulted in 399fps w/0.20's. Great for outdoors.

Shorter M4 CQBR inner (shorter than what the cylinder called for) shot 345fps. Great for indoors.

So...either swap uppers/barrels/etc...or just swap the inner barrel to result in two different FPS' for different scenarios.

So the gun was really setup for 400fps...then I cheated the system and made it less effecient with a short barrel to kill off speed.

[cetane]

I did some tinkering with my m4. CQB'ish barrel with m100 shoots about 400 (+/- 3) with a ported cylinder. I put a piece of aluminum foil duct tape over the port & it dropped to 370. Didn't try shooting targets to see how it effected that but with like a m95 spring it could get you to below 350 for indoor & 380'ish for outdoor. $0.02...

[lurkingknight]

Originally Posted by Azathoth

If you own two P90 lower frames or bodies then I don't understand why you would even be asking this question as you would have 1 gun to pickup for the field and another for CQB.

I have 2 uppers, 1 body. The 2nd gearbox that was shipped to me (original TM) is in pieces and the gearset for it is wrong, they bind in the rotation, I'm guessing they got mixed up with another set of gears or something is twisted.

The p90 is easy to swap out gearboxes, but I'm installing a mosfet, and changing the wires every time can be a pain, or changing the trigger group, I don't want to overwork the crappy metal in the gearbox casing and strip a screw hole and be out a gearbox.

If people have done it with success, I may try it later on, when I have a setup properly working, as it is right now, it's still in a few incomplete pieces, and lacking a lipo heart.

The spring in the gearbox currently is a sp120, I have an M100 and sp110 as well I can try later on once I get my hands on a non ported cylinder and a second barrel.

Originally Posted by m102404

Don't know about the P90....but I did that with M4's.

SIG length inner barrel....resulted in 399fps w/0.20's. Great for outdoors.

Shorter M4 CQBR inner (shorter than what the cylinder called for) shot 345fps. Great for indoors.

So...either swap uppers/barrels/etc...or just swap the inner barrel to result in two different FPS' for different scenarios.

So the gun was really setup for 400fps...then I cheated the system and made it less effecient with a short barrel to kill off speed.

what spring were you using?

with the sp120 and whatever guarder bits are in there, this gearbox is doing about 405-410 with a 247mm 6.03 (or .02? it's a madbull) barrel (regular p90 length)

[m102404]

I think it was a s110...can't remember.

I basically built it to field length and power level...then used a shorter barrel to kill off the FPS, and the front end I was using (JP) had a bunch of different barrel length screw on bits....so I just changed out the end of the barrel/flashhider for field vs. CQB

[ThunderCactus]

It's less work to change the spring than the cylinder.

[lurkingknight]

think you missed the intent :P

[ThunderCactus]

I'm just saying, you can run it 350fps indoors and out, you don't need a 400fps gun outdoors, you're not going to see a huge difference in range there...

[lurkingknight]

probably not... but I'm just trying to find a practical use for the 2nd receiver :P

[ThunderCactus]

one RIS with laser and flashlight, one with just RDS, for an indoor/outdoor setup? lol

[mrbishi]

If you just have a weaker spring you wont be putting the GB under as much strain, back home some cowboy retailers & owners drill cylinders and nozzles as a quick & cheap downgrade method, to get her under the Joule, but fail to see the inefficiencies of such.

To me its like driving around with your handbrake on to keep it under the speed limit.

If you're wanting to separate GB's for indoor and outdoor games or whatever just use the correct spring and fire away.

[Styrak]

Originally Posted by lurkingknight

probably not... but I'm just trying to find a practical use for the 2nd receiver :P

Fix the other lower receiver, have 2 separate guns.