CA M14 FPS Efficiency

[pestobanana]

So I'm duped. My M14 doesn't necessarily have a bad air seal, it will shoot whatever speed in m/s the spring is rated for. I'm looking to get it up to the level that my other guns are at. My G36 gets 445fps with my M120, but my M14 gets 40 fps lower than that with the very same spring. At one point my G36 was getting 405FPS with a M100.

I've checked air seal in the gearbox and it's perfect. I've also swapped and played around with every single air seal component, without much of an increase in efficiency.

Any ideas on what it might be? Help and suggestions appreciated!

Here's a list of parts I've tried:

Hop up unit: CA metal, Lonex
Hop up rubber: CA stock, PDI W-Hold, Guarder Clear, A+70, Prometheus soft
Barrel: CA tightbore, Prometheus 509, Prometheus 550
Cylinder: CA stock, Modify
Air Nozzle: CA stock, Modify AUG, Lonex M14
Piston: CA yellow, Lonex Red, Modify Quantum
Piston Head: CA metal, Modify Aluminum, Lonex POM, King Arms metal

[Styrak]

Whether you have a bearing on your spring guide or piston head can also affect what your gun is shooting. And different guns will shoot different FPS with the same spring, just because of different air seals from the design of the gun and also the length inside the mechbox where the sprin sits.

445fps is extremely high for an M120. 400ish is the normal range for that spring.

[pestobanana]

I thought it might have been gearbox length, but when I measured the distance from the back of the piston in a fully forward position to the back of the spring guide, it was the same as on my V2 and V3 gearboxes.

My pistons and spring guides all have bearings.

Would you have any idea on how to seal up some of these leaks? I'd prefer to get as much mileage and efficiency as I can when I run heavy springs.

Thanks

[ThunderCactus]

Did you test the mechbox for air seal?
If you have perfect air seal, the piston will not move AT ALL when you test for compression. Make sure the tappet plate is forward too, I've seen leaks of up to 50fps between the air nozzle and cyl head

[Styrak]

Originally Posted by pestobanana

I thought it might have been gearbox length, but when I measured the distance from the back of the piston in a fully forward position to the back of the spring guide, it was the same as on my V2 and V3 gearboxes.

My pistons and spring guides all have bearings.

Would you have any idea on how to seal up some of these leaks? I'd prefer to get as much mileage and efficiency as I can when I run heavy springs.

Thanks

Like I said, 400fps is normal for an M120 spring. Your M14 is normal, sounds like no air seal issues.
It's your G36 that's the abnormal one.

[pestobanana]

Originally Posted by ThunderCactus

Did you test the mechbox for air seal?
If you have perfect air seal, the piston will not move AT ALL when you test for compression. Make sure the tappet plate is forward too, I've seen leaks of up to 50fps between the air nozzle and cyl head

The piston does not move at all. I was having that issue when I tested with a Modify air nozzle, but when I switched to Lonex nozzle and cylinder head the air seal was perfect.

I guess I'll have to just accept that my G36 is abnormally awesome and my M14 is just normal awesome lol.

[ThunderCactus]

Yeah, it's not unheard of.
My G&P 249 when I first got it tended to get an extra 20fps out of any spring I put in it. Some guns are just better than others lol

[Hectic]

Cylender volume vs barrel volume will also make a big difference. An example is in a vsr 10 the optimal barrel length is 500mm. When you start going to say a vsr10 gspec you will notice a huge rediuction in fps so say you have a full cylender ( no hole) and are running the "socom" style front set with the short inner barel you will have a lower fps the the same gun with a full sized front end with the long inner
http://arniesairsoft.co.uk/?filnavn=...andbarrels.htm
That link will help you figure the best barrel length for your cylender (longest one for the cylender is best)
Back to the vsr when using a gspec the inner barrel is ony 330 mm or shorter 313 depending.
Running that on the same setup as a 500mm one will lose up to 100fps. By shortening the compresion zone on the cylender the fps will go up once you shorten it enough the cylender and barrel will be matched thus no wasted air and the same or simaler velocity with the same spring on a shorter barel
Example
With the following compression zone lengths the 313mm length barrel chrono'd as such:
93mm ~400fps (no hop) ~6mm was taken off from 1st Project
79mm ~430fps (no hop) +30
70mm ~458fps (no hop) +28
64mm ~478fps (no hop) +20
64mm ~510fps (hop set for bb retention)
You can see how the fps goes up as the cylender is made smaller to compensate for the shorter barrel
Here is where the info came from
http://www.airsoftretreat.com/forums...?topic=88662.0

[pestobanana]

Hectic I've swapped barrels and cylinders between the two guns, barrel length isn't the issue. At the moment they're both sporting CA stock cylinders and Prometheus barrels. I've swapped the two barrels between the guns and there hasn't been a difference.

[Hectic]

CA stock cylender doesnt mean anything they make cylenders in all sizes (read port location) as an example a jg m4 can come with a 3/4 or a 4/5 port tho most will always have a 363 mm inner swapping to a 430 or 460 in those cylenders will increase the fps. If they both have the same pot location on the cylenders then you should expect simaler results between the different barrel lengths. Conversly if they have different cylenders going to an inner that is longer then the volume wouldnt really decrease fps but it would increase stress on the mechbox at the cylender head due to the airbreak effect the bb has while its in the barrel once the bb exits if the piston isnt fully forward it will slam forawrd the rest of the way alot harder then if the bb was still in tye barrel.
At any rate i wasnt sure if this was your issue i just thought id suggest it incase it mayne was causing the problem. Not that its a huge problem just tryin to figure why the fps difference.

Another thought is if its the exact spring in the two guns or just the same spring and rating as they could vary from batch to batch or even be misslabled say a 130 in a 120 package or what have you
Edit i re read and see its the same spring u are using

[pestobanana]

They are both unported stock CA cylinders, and I've even swapped them around, along with the piston/piston head assembly. It's the exact same spring I even checked with other springs and the G36 is consistently 50 fps or so above the spring rating, and the M14 is right where the spring is rated.

I'm just OCD so I'm trying to figure this out lol

[Hectic]

Lol no worries it seems a lil odd to me too ive seen 10-20 fps but 40 seems a lil much especially when uve take care of the rest of the variables.
Only other one i didnt see you mention is the hop up rubber tho id find it hard to create a 40 fps diference there but i guess it could be posible from an extreemly hard to an extreemly soft rubber

[pestobanana]

I tried testing all the hop up variables too, changing barrels, air nozzles, hop up units, rubbers and even nubs.

Hop up units: CA metal, Lonex
Hop up rubbers: CA stock, PDI W-Hold, Guarder Clear, A+70, Prometheus soft
Hop up nubs: CA, Guarder, Prometheus soft, Firefly flat, Prometheus bridge, SCS
Barrels: CA tightbore, Prometheus 509, Prometheus 550
Air Nozzle: CA stock, Modify AUG, Lonex M14

I just found it odd, because there is no apparent reason for this 50 fps difference.

[pestobanana]

UPDATE

Performed the following mods:

Sanded front of tappet plate, heated and bent for better alignment
Reshimmed hop up unit, using cardstock and O-rings
Relubricated hop up unit

Installed the following:

SHS Steel Cylinder
Prometheus Metal Piston Head
Modify 18:1 Gear Set
Modify Moundless Hop Up Rubber
Prometheus Bridge Tensioner

Chronoed today at Toronto Airsoft, same MadBull M120 and .2 Bastards
High: 455.7 FPS
Low: 455.1 FPS
Drops to 448 FPS with hop up dialed in.
I've never seen a gun chrono so consistently before, I guess I finally got that perfect air seal. I always thought +- 1 or 2 FPS was good, but I guess +- 0.3 is my new goal for the rest of my guns.

Current Internal Setup:
Lonex Enhanced Aluminum Cylinder head
Lonex Air Seal Nozzle
Lonex Hop Up Unit
Madbull M120 Spring
Modify Gear Set
Modify Quantum Piston
Modify Bearing Spring Guide
Modify Moundless Hop Up Sleeve
Prometheus Metal Piston Head with Bearings
Prometheus Soft Bridge Tensioner
Prometheus 6.03mm 550mm Tightbore Barrel
SHS Full Cylinder

[lurkingknight]

time to rrrrrrrrrr-hop that pitch.