Upgrading a SRC M4

[bareass]

Hey all,

I'm planning to upgrade my SRC M4A1. it currently has a S90 spring in in, and is shoot around 300 (.2g) i would like to up that and some other internals, but need to be able to go down to 350 for some fields.

what are my options?

I was thinking of a madbull ultimate hop up, with with the 6.01 barrel.
should i upgrade the piston/cylinder? i was thinking of a bore up kit.

need some options!

thanks.

[SniperSam]

wouldnt go for that tight a barrel for fps increase... a new hop up would be in order however

[bareass]

the tightbore falls under the "other internals" catagory... i want it to tighten up the groupings and add some range over the stock barrel. not sure if i'm going to go 6.03, or 6.01.

[bareass]

so i took apart the the gun just now, and was planning on cleaning the hop up rubber, and checking the air seal.

aside from feeling pretty ripped off about buying this gun used. (upper reciever is broken, there's a stripped screw in the gear box, and the clip for the hop up is broken, among other general misuse signs on the lower receiver) i noticed that my cylinder is full seal. that would explain the sound it make, would that also explain the low ROF this gun has?

also, i know having an unmatched cylinder/barrel would result in lowered FPS, but how much? how much FPS would i gain if i installed an M16 length barrel?

[Kos-Mos]

What do you mean the sound it makes? A too large (unported) cylinder won't make the gun sound different. Your piston is probably stripped and/or gear axle broken.

I would recommend you to get a 6.03 tightbore if you want one. Prometheus are really good, but expensive. Madbull's 6.02 are good too if you are on a budget, but expect to have to change it in about 2 years (the finish wears off).

The flaw in SRCs are the gears. Replace them as soon as you can. The gears temselves are not bad, but the axles are breaking off. I have issues with my bearings too. The flange is disconnecting from the bearing body. A good set of bearings is in order too.

The stock piston is horrible. Replace with a TM or Modify Ultra speed (the white one).

Cylinder is ok, if you want a ported one take what ever brand you want.
Cylinder head is great, but no sorbo or rubber pad. It can be replaced with a better one or remove the o-ring that serves as a padding and install a sorbo kit.

Piston head is aluminium. This is user preference. If you want to keep it, it is very good quality.

Spring guide is bearing and aluminium. No need to change it.

Stock spring usually will kick 430 fps. I guess that is not your case.

Stock nozzle is a regular TM style. No sealing rings. You can replace with a Modify air seal nozzle.

Stock hop-up rubber is a bit soft. Stock chamber is quite good. AVOID THE MADBULL ULTIMATE. Over 50% of the users have issues with it. If you really want to change it, go with Systema, King Arms or Guarder.

Stock motor is really good. It cranks the M135 spring easilly, so with a softer spring it is a beast.

Tappet plate and selector plate are reinforced nylon composite. They are better than even the red King Arms ones.I needed to grind mine for a mod and it was hard to work even with a dremell tool.

In summary:

MASK DUO cylinder/piston head kit
Modify Type 1 cylinder (for M4 barrel)
Madbull M4 tightbore
Guarder clear hop-up rubber
Modify M100 spring (should bring you around 330-340fps)
TM or Modify piston
Modify 7mm bearings or bushings (I go with the ceramic ones)
Modify High speed gear set (They have the same ratio as the stock gears)

If you want to save a bit, leave out the MASK kit and bearings for now. You can also wait for the gears, but it sucks to break them just before the game and then wait 2 weeks for replacement.

[bareass]

hey Kos-Mos I'm not sure that we are talking about the same SRCs, i have a Gen 3 M4A1,
it uses an M120 spring and apparently better gears then the older ones, with 8mm bearings. if this is the same one you're talking about please confirm.
my motor doesn't seam to be all that great, i had a doc at a game look at it, he hooked it up to a lipo and it was still pretty slow, but that could be just old, i'm likely going to be changing it.

i was thinking of getting a sorbo pad, but that you mean i would have to change the cylinder, correct? i thought that is what i have read. at any rate, i'm getting 100% air seal from the on the piston and cylinder head, but not the nozzle, so that is going to be changed.

as for the cylinder, i was thinking instead of changing the cylinder, i would get a M16 length barrel (509mm). this would optimize my system and up the FPS right. but how much, or how much would it drop if i put the stock barrel back in?

[Kos-Mos]

SRC Gen III.

The gears are better than the older ones, made of steel and very well made. But the axles are brass and they break. On every rifle I had and worked on, I had to replace the gears.

The 8mm bearings are very weak. They won't crush like most cheap ones, but the flange that holds the bearings in the mechbox are barely forced in place. On my gun, two of them broke off and the bearing can move out of the mechbox because of that (screwing shim job at the same time). Changing theses might actually save the gears as when they break, there is a small metal ring that is let loose in the mechbox and the gears alignment is changed.

My SRC motor was really great. If you happen to change yours, let me know. I wanted to rebuild mine with better quality wire and hand wrap it for better efficiency and torque (I am an RC guy). The SRCs have very nice open case design that makes that easy.

The stock cylinder head is not a TM based design. You won't be able to install a sorbo pad properly like most other brands. The head is aluminum without the recess for the rubber pad. Instead, they placed an o-ring in a groove to "dampen" the noise. I can tell you that my rifle snaps a lot more than anything else I ever had. For a V2, not the best thing in the world. Might be what you where referring about the sound.

You can still run your rifle with the short barrel and full cylinder. It might damage the mechbox over time because once the BB leave the barrel, there is still a significant distance in the cylinder and the piston slams on the cylinder head. You will also notice a drop in FPS of about 10-15FPS, because the piston is not yet accelerated properly when the BB leave the barrel, wasting a lot of energy. You also won't notice a difference between a M4 barrel and a M16 barrel. A cylinder change would be a better idea for long-term.

The spring is "supposed" to be a M120, but both my G36 and M4 chrony at 430 fps with the stock spring (it is silver with no tight section), suggesting that it is around a M130/M135.

[bareass]

thank you, i had thought that a full seal cylinder was the correct one for an M16, thats why i was going to switch. i rather have the longer barrel, with the ability of shortening it to drop FPS if need be. also, the cylinder head on mine is plastic. and looks like it has a sorbo type thing on it. either way it looks like it is in good shape, and has good seal.

[bareass]

so from what i've read, the full seal cylinder is for long barreled riffles. is this correct?

if so what i plan on doing is running a 509mm inner barrel (M16) with a silencer to cover it up. from my math that means i need to cover up 146mm, so a 150 or 180mm silencer should work. can someone confirm this?

with that set up i should be run upto 360-370 fps. and swap back down to my stock inner barrel to drop me down to 350 for when the need arises.

does this make sence or am i missing something?

thanks a ton for all the help so far. i think i'm just about ready to buy!

[CJay]

I'd second alot of what Kos-Mos says however I'll add a couple bit here - yes your gun will sound a little different with the full cyllinder (unported) reason being is that the compression cycle is let loose right after the bb exits the barrel. wrong length barrel for matched cyllinder and ur left with no backpressure from the bb and piston slams full force into the front of the mechbox - FYI this reduces the life of the mechbox itself and potentially breaks the front off of it so that is NOT GOOD. SRC are complete idiots for installing every gun they made in the gen3 line with unported cyllinders - even the CQB guns - gives them a nice sharp crack sound but that means more impact and more stress on internals (mostly the gearbox itself) so my advice is either stick with long barrel full cyllinder or a barrel under 455mm and get a ported cyllinder. now onto the aluminium pistonhead - The first thing I'd be doing is sorbo that guy up. as people have mentioned the stock src spring is damned heavy so the aluminium gives the piston a bit more inertia - not a big deal usually but i can and will sometimes cause the mechbox a little more stress than is advisable. U can definitely sorbo up ur cyllinderhead but what u need to be doing is then filing off the second tooth on ur piston (the second from the back) and this will stop the gears from grinding the small tooth there and getting plastic pecies into the mechbox. all this has been bourne out through my experience as a guntech so i'd look into doing this first - in my experience these problems are ur biggest thing right now.

[bareass]

do i need to grind off the second tooth if i only put a sorbo on the piston? or is that only when u sorbo the cylinder head?

[Kos-Mos]

You always install the sorbo on the cylinder. The piston has some ports on the head and theses are needed for good seal.

In this case, the SRC green piston is quite bad. You should change it for a Modify Ultra Speed piston that does not have a second teeth already.

[bareass]

alright so i have a parts list together at airsoftparts.ca...

modify high speed ultra piston
sorbo pad - new version
modify air seal nozzle
guarder clear rubber
mad-bull hop-up c-clips (mine broke)
mad bull 6.03mm barrel - 509mm length
tactical nato 5.56 silencer
silicone spray.

seams like a pretty decent list so far.
anything i missed, or anything you would change?
thanks for all your help so far everyone!

[bareass]

Originally Posted by bareass

modify high speed ultra piston
sorbo pad - new version
modify air seal nozzle
guarder clear rubber
mad bull 6.03mm barrel - 509mm length

thought i'd report my finding, its been a while, but it took time to get to a chonie.

so those are the parts i installed. the sound is much different thanks to the sorbo, and proper length barrel. i gained about 20-25 fps doing this change.
not that came from the inner barrel and the nozzle. how ever my nozzle had a pretty good air seal, i just wanted 100%. so this mainly came from the inner barrel.