I need to drop fps....and I don't know how!!! - Airsoft Sniper Forum
       

Go Back   Airsoft Sniper Forum > General > The Lounge
The Lounge Off-topic chat. Speak your mind!

Like Tree13Likes
Reply
 
LinkBack Thread Tools Display Modes
Old 01-23-2020, 09:46 AM   #1
Experienced Sniper
 
Zero Roaster's Avatar
 
Join Date: Mar 2017
Location: Canada
Posts: 1,566
Laughing I need to drop fps....and I don't know how!!!

I wasn't sure where to post this, so when all else fails, take it to the bar...

So, here's the deal, our 'legal' limit here in Canada is a minimum of 366 fps. There's a CQB field in Calgary where the limit is 350 max...I know it's complex, here nor there.

Anyhew, Young Sasquatch is moving to Calgary next summer and we were bs'ing about hitting the CQB field after we move him into his place. But here's the rub, nothing in the closet is under 390 fps...and that's already sand bagged!

So, he's got this neat little G&G MP5, shoots like a DMR at 410fps and handles .3's like a boss. I was thinking of moving the port forward and finding a wet noodle for a spring to hopefully drop it like a rock to about 340.

Thoughts? Ideas? Discuss...
__________________
...and nary a whisper was heard..
  Reply With Quote
Remove Ads
Old 01-23-2020, 11:56 AM   #2
Nilye   Nilye is offline
Young Gun
 
Join Date: Jun 2018
Posts: 47
Dont know if piston head from gearbox v2 will fit but you can do this:
https://www.leesprecision.com/cnc-ma...-head-pro-pack
Great precision.
Michal
Zero Roaster likes this.
  Reply With Quote
Old 01-23-2020, 12:01 PM   #3
Snappuh   Snappuh is offline
Young Gun
 
Join Date: Feb 2014
Posts: 6
Well from what I’ve read you likely have more experience with AEGs than I do, and your plan is exactly what I would do. And have done. But I guess I will offer my limited experience anyway.

I actually had a hard time getting an ICS CXP (the really short barrel version, not sure on the specific model) down to ~300 w/.20 without chopping my weakest spring (from the junk parts box) down to where it almost has no pre-load. I do have a standard M4 ported cylinder in there so it is probably over volumed at least slightly but I’m not concerned with it since it’s a CQB gun only- I run lighter cheaper bbs in it since range and accuracy is not a high concern. That reminds me, porting and volume balancing do help with energy efficiency so using a different ported cylinder may actually allow, or rather, force, in your case, you to use a weaker spring yet. I haven't played around with with porting/volume balancing much but it makes sense that giving the piston more time to accelerate will net you more energy efficiency as long as you are not under-volumed.

But yeah. I did exactly what your plan is (without all the crap I ranted about concerning volumes) and it worked out.
Haven’t checked joule creep in my ICS but I would imagine it is at least moderate in my short tight barreled build. As long as you know they don’t chrono in joules you should be good to aim for that velocity w/.20.
Zero Roaster likes this.
  Reply With Quote
Sponsored Links
Advertisement
 
Old 01-23-2020, 12:48 PM   #4
Experienced Sniper
 
Zero Roaster's Avatar
 
Join Date: Mar 2017
Location: Canada
Posts: 1,566
Yeah, my specialty is long range AEG's...usually when I see a 350fps gun on my bench, it's broken! hahahaha

That's kind of what I figured, 60 fps is quite a drop, so maybe I'll try an M90 and I have a crappy ported cylinder that should bleed off quite a bit of air...seems almost a shame to stifle such a neat little gun.
__________________
...and nary a whisper was heard..
  Reply With Quote
Old 01-23-2020, 01:25 PM   #5
Advanced Sniper
 
Corriander's Avatar
 
Join Date: Jan 2014
Location: Louisiana, US
Posts: 879
Spring rate, cylinder volume and barrel length are the determinants of output energy on an AEG. You’re already on the right track.

Since TCA added their SMG class that is limited to 1j, there has been a local influx of dedicated builds. Most of us are running P90’s, EVO’s and MP5’s.

Half-volume cylinders are the norm with whatever spring thrown in that roughly gets to the limit. Fine spring tuning is then done by clipping or preloading with spacers to settle in right at a few FPS below limit.

While not part of the compression components, make sure to appropriately downsize you motor and battery to avoid unpredictable precocking or double firing.

Everything else is pretty much the same as a respectable AEG build - well shimmed gears, reliable hop/bucking/piston/etc, decent quality barrel and MOSFET if you’re using a lipo.
bmr3 and Zero Roaster like this.
__________________
Beware the tactical kitty ears
  Reply With Quote
Old 01-23-2020, 01:41 PM   #6
1tonne   1tonne is offline
Veteran Sniper
 
1tonne's Avatar
 
Join Date: Jun 2012
Location: New Zealand
Posts: 4,821
EDIT: (I see Corriander has beaten me to it)


Here are some things that may help


-Cut coil off of spring
-Add weight to the piston
-Make the port smaller (Sometimes if it is a short barrel, you can even put in a full cylinder and you will lose fps)
-Put in a shorter inner barrel (at least with this you do not have to pull apart the gearbox)
Zero Roaster likes this.
__________________
Live in New Zealand and want Action Army Parts? Check out this thread:
https://www.airsoftsniperforum.com/sh...807#post160807

Advanced VSR Sniper Building Guide
https://www.airsoftsniperforum.com/showthread.php?t=6075
Advanced L96 Sniper Upgrade Guide
https://www.airsoftsniperforum.com/showthread.php?t=6465
Choosing the right spring and making it work
https://www.airsoftsniperforum.com/32...tml#post127126

Last edited by 1tonne; 01-23-2020 at 01:43 PM.
  Reply With Quote
Old 01-23-2020, 04:17 PM   #7
Experienced Sniper
 
Zero Roaster's Avatar
 
Join Date: Mar 2017
Location: Canada
Posts: 1,566
Hey Corriander, thanks for the tip about the motor and battery...excellent point. Cut off its fuel supply....I like it!!
__________________
...and nary a whisper was heard..
  Reply With Quote
Old 01-23-2020, 04:25 PM   #8
Snappuh   Snappuh is offline
Young Gun
 
Join Date: Feb 2014
Posts: 6
Oh yeah! Forgot the rest of my internal build and what Coriander said about overspin reminded me: JG hight torque blue motor, standard ratio gears, 7.4 lipo, NO mosfet, Stock ICS piston and head, stock cyl head and nozzle, ICS hop chamber(required, thanks to ics specs being proprietary for hop chamber/nozzle relation), 6.035 1714 alum arrow shaft barrel(never measured exact length, no more than 220mm I’m sure) with silicone tubing section over window and probably a SHS 70deg bucking over that. Pretty much all applicable air seal mods(outside of chamber/barrel) have been done along with AOE and hammars silicone cyl head mod.

I am fortunate to never get close to having double shooting or partial pre-cocking with the 7.4v but it does try to with an 11.1v, Id say it does about 30-40% precocking every other shot, meaning: first shot = little overspin. Second shot = normal. Third shot = little overspin. Fourth shot = normal, etc. So I just stick with the 7.4. I never use full auto anyway.

Also forgot to mention another thing I’ve never tried: short stroking your piston/gears. It would be a lot more invasive than just messing with springs and cylinders but may be worthwhile if you really want to play around with performance. A few years ago I was very tempted to do a dsg build just for the trigger response and it would be so easy on an ICS. Maybe I will some day.
Zero Roaster likes this.
  Reply With Quote
Old 01-23-2020, 04:59 PM   #9
cetane   cetane is offline
Jr. Sniper
 
cetane's Avatar
 
Join Date: May 2013
Location: Markham & Stouffville, Ontario, Canada
Posts: 449
I’d just start with a generic brass barrel and start chopping it down while chrono checking it with 0.20’s until you hit your sweet spot. It may be over volumed like crazy, and probably will creep energy, but it’ll get you to cqb speeds without gb disassembly.
Zero Roaster likes this.
  Reply With Quote
Old 01-23-2020, 09:36 PM   #10
Advanced Sniper
 
Corriander's Avatar
 
Join Date: Jan 2014
Location: Louisiana, US
Posts: 879
Quote:
Originally Posted by Zero Roaster View Post
Hey Corriander, thanks for the tip about the motor and battery...excellent point. Cut off its fuel supply....I like it!!
Once upon a time I put a magnum motor with a massive 11.1v lipo in to an MP5K with a 90mm barrel. It was loud as hell a drained a mid cap in under 2 seconds. Completely impractical on the field but it certainly carried an intimidation factor.
1tonne, Zero Roaster and Jbrinker1 like this.
__________________
Beware the tactical kitty ears
  Reply With Quote
Old 01-24-2020, 01:29 PM   #11
Experienced Sniper
 
Zero Roaster's Avatar
 
Join Date: Mar 2017
Location: Canada
Posts: 1,566
Quote:
Originally Posted by Corriander View Post
Once upon a time I put a magnum motor with a massive 11.1v lipo in to an MP5K with a 90mm barrel. It was loud as hell a drained a mid cap in under 2 seconds. Completely impractical on the field but it certainly carried an intimidation factor.
Y'know, contrary to every engineering bone in my body, sometimes impractical is WAY more entertaining. That in itself is something worth thinking about. After all, this is still a game, right?

Hey Cetane, I'm digging the idea of the brass cylinder...

Now about that whole super modified DSG/short stroke business...I'll let that pass. I'm still very much a one shot type of guy. If I CQB, it's a 1911, and a revolver with shotty shells...no rifles.
__________________
...and nary a whisper was heard..
  Reply With Quote
Old 02-15-2020, 08:09 AM   #12
Jr. Sniper
 
BlackDogAirsoft's Avatar
 
Join Date: Nov 2019
Location: Earth
Posts: 457
You could buy a new spring. Other than that, this is a bad idea, but stop your aeg at half cycle I.e. with the spring compressed but don't fire it. Leave it like this overnight.
Otherwise just cut the spring.

Sent from my SM-A505FN using Tapatalk
Zero Roaster likes this.
__________________
Hidden by the leaves...
SiliconSword told me to add the following:
(\ __ /)
(= '.' =) This is a little rabbit.
(") _ (") Copy / paste it into your signature to help it dominate the world.
  Reply With Quote
Old 02-15-2020, 08:41 AM   #13
Young Gun
 
chainsaw squirrel's Avatar
 
Join Date: Aug 2017
Posts: 34
Quote:
Originally Posted by Zero Roaster View Post
I wasn't sure where to post this, so when all else fails, take it to the bar...

So, here's the deal, our 'legal' limit here in Canada is a minimum of 366 fps. There's a CQB field in Calgary where the limit is 350 max...I know it's complex, here nor there.

Anyhew, Young Sasquatch is moving to Calgary next summer and we were bs'ing about hitting the CQB field after we move him into his place. But here's the rub, nothing in the closet is under 390 fps...and that's already sand bagged!

So, he's got this neat little G&G MP5, shoots like a DMR at 410fps and handles .3's like a boss. I was thinking of moving the port forward and finding a wet noodle for a spring to hopefully drop it like a rock to about 340.

Thoughts? Ideas? Discuss...
Not a big expert on AEGs, but what I do know works is running the battery down a bit before taking it to the game. Once charged, fire it full auto for like 10 seconds straight a few times. That'll get rid of that big power spike from the peak of the battery's charge.
Failing that, try a lower power battery then adjust the weight on your piston if you need to step it up a bit.

Note that batteries are a little like gas power in a small way. Even when it seems like the battery is fully depleted, their power supply bounces back slightly when allowed to recover. But this happens no matter what the charge state of the battery is. With gas this is obviously because the gas is given time to reheat and gain extra energy from the surrounding atmosphere. No idea why this happens with batteries tho, but it's something I've noticed in lots of things. I had a lot of battery powered toys when I was a kid lol.

EDIT: if you're still interested, perhaps it's the heat built up that increases internal resistance in the circuits and motor which creates this effect, and therefore the efficiency of power usage is reduced, until the circuits and motor cool down. Also of course, as the battery loses charge, its power output will go down, so there's that too.
Zero Roaster likes this.
__________________
TM l96

PDI 6.05 stainless inner barrel
Maple leaf autobot 60C bucking
Action army Teflon cylinder+head
Airsoftpro 90 degree trigger
Airsoft pro piston (2015)
Airsoft pro m160 spring
Airsoft pro spring guide 13mm

Last edited by chainsaw squirrel; 02-18-2020 at 02:22 PM.
  Reply With Quote
Old 02-15-2020, 02:27 PM   #14
1tonne   1tonne is offline
Veteran Sniper
 
1tonne's Avatar
 
Join Date: Jun 2012
Location: New Zealand
Posts: 4,821
Quote:
Originally Posted by chainsaw squirrel View Post
Not a big expert on AEGs, but what I do know works is running the battery down a bit before taking it to the game.
Battery strength does not effect fps. It only changes the cycle rate.
What changes the fps is the parts inside the cylinder and your barrel length as well as you air seal between the air nozzle and the bucking and also how much hopup is applied. Work with these and it will make a change in the fps.
Zero Roaster likes this.
__________________
Live in New Zealand and want Action Army Parts? Check out this thread:
https://www.airsoftsniperforum.com/sh...807#post160807

Advanced VSR Sniper Building Guide
https://www.airsoftsniperforum.com/showthread.php?t=6075
Advanced L96 Sniper Upgrade Guide
https://www.airsoftsniperforum.com/showthread.php?t=6465
Choosing the right spring and making it work
https://www.airsoftsniperforum.com/32...tml#post127126
  Reply With Quote
Old 02-15-2020, 08:31 PM   #15
SHEED   SHEED is offline
Young Gun
 
Join Date: Apr 2019
Location: New Zealand
Posts: 18
For my DSG build I got everything running perfectly, no double strokes, no pme etc. Only to find once chronoed on .30g that it was over the local limits. So the only part I wanted to change was the air nozzle. I got a spare plastic one and filed it down very carefully. Went from 1.30j to 1.08j. Right were I wanted it under the limit with some headroom in case I run .28s.

In short - you could file the front of the air nozzle. Or spend $$$ and get the retro arms adjustable air nozzle.
  Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -5. The time now is 01:16 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
SEO by vBSEO ©2011, Crawlability, Inc.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.