What else do i need for my spr to take a sp120?

[Comrade Commissar]

I was thinking of selling my D-Boy Spr but now it seems more economical to just keep it. The gun shoots far but the FPS is a little low for me (275 with a .25 i believe). I first thought to make it a DMR, however i think its better to just push it close to 400 since it can already reach out and touch some one with such a low fps. I have the spring sitting in my parts box but i haven't thrown it in yet as its a bit of a demon spring (ill get to that below)

Ive thrown a tight bore in and I have upgraded the internals almost completely from stock but a few stock elements remain. Basically the one upgrade i think i need to change is the bushings, as they are plastic, i need to change them to metal ball bearing ones correct? Is this the only modification i still need? Or should i also go with a new set of gears? Will i also need a high torque motor to replace the stock one soon? I'm assuming I'm gonna burn the stock one out with the sp120.

Also this same guarder sp120 spring i want to use was in my friends D-boy m4. It shredded his stock piston (no surprise) but it also shredded the ICS aluminum piston he used to replace it, stripped 2 teeth off a gear, and ate up his cut off lever to the point of shooting in only full auto. After that incident we returned the spring to stock and i became the owner of it. Do i run the risk of having the same problem? should i even bother? Do i run the risk of breaking the front of the stock box off too?

Here is a list of what i currently have in the gearbox that is upgraded.
CA m4 nozzle
Bravo Cylinder head
Modify Type 0 cylinder
Modify Bearing piston head
area 1000 spring guide
King Arms pom piston with 7 metal teeth

[XavierMace]

Before replacing the spring you need to find out why it's shooting so low to begin with.  Most of the chinese guns are shooting ~400 with .20's out of the box.

[Comrade Commissar]

Well, thats a bit of a mystery... Its supposed to shoot high out of the box (385, higher than the m4)...

I had it chrono'd in colorado at the local shop before i left, they said that was "normal" and alot of their guns chrono low. I second guessed it still and they said alot of guns dont have that high of an fps... I couldn't believe it really, especially since it shoots so far... Is it possible their chrono is just messed up? Should i get another opinion? They just used some random unlabeled bbs, and the first battery they could find that worked... the only thing i can think of is that the motor might need to be adjusted... as it hadnt been since the last reassemble. But i dont know if thats got anything to do with fps... I asked if the battery was fully charged, or on its last legs, and they said that shouldnt matter but that it was, however i dont know that they really knew...

Ive heard of torn hop up bucking causing a decrease in fps, but the stuff i just put in there is brand new (maybe i messed it up, but it looked fine when i installed it). Im pretty sure the piston head isn't loose either as i loctited it in (not with the perm. stuff)... Gear grease was used for the cylinder/piston instead of the normal piston grease as it wasnt around at the time. I know its a bit thicker, but it shouldnt cause an almost 100fps decrease...

im stumped...

[XavierMace]

A torn bucking would decrease the FPS but your accuracy would also be gone as well.  First thing to do it get it rechrono'd to confirm what it's shooting at.

[Shadow]

Even though a bucking may be new, all it needs is a miniscule tear right near that nub to cause a problem... and that often happens during installation if one is not careful or methodic when installing it.  Some of those edges on a barrel can be pretty sharp, and the fit is very tight.

[axisofoil]

nozzle can cause huge problems with fps too, but usually also hurts the accuracy. Really, aside from a low-rate spring, most of the other fps problems cause huge accuracy issues.

But, for your upgrade, you might need a new motor.
You will definitely need new bushings (and shims also). Ball-bearing aren't necessary, and solid bushings are more than enough for all but the highest ROF setups imo.

an sp120 isn't that high rate of a spring... you're not running the risk of really breaking much besides a plastic spring guide or wearing through the plastic bushings (and even that would probably take a while). You have an awesome piston already and have upgraded the guide... so do the bushings and shim everything up. The stock motor might be an issue... I know the stock dboys motor in my AK pushed an sp120 without complaining.

If the gears are missing teeth (you said that some teeth got stripped off of one at some point), replace them. I wouldn't worry about buying top-of-the line gears... they aren't really necessary for a normal build.

[Comrade Commissar]

nozzle can cause huge problems with fps too, but usually also hurts the accuracy. Really, aside from a low-rate spring, most of the other fps problems cause huge accuracy issues.
 
If the gears are missing teeth (you said that some teeth got stripped off of one at some point), replace them. I wouldn't worry about buying top-of-the line gears... they aren't really necessary for a normal build.

As for the nozzle, its possible that i have the "wrong" nozzle. I was unable to determine if the Dboy rifle used a m16a2, m4, or m16a1 style nozzle, to my best ability i decided the gun was over all a clone based on the m4 series, not a m16a2 or m16a1 tm/ca style which take a slightly different nozzle. However i could have been wrong.

My gears are fine, it is the gun that this spring was previously in that suffered that catastrophic incident, i mentioned it as it was another d-boy and it pretty much seemed like the spring tore the gun apart from the inside out. The piston being Aluminum probably contributed to the stripping. My friend probably messed up his shimming when he threw it all together too though... causing the stripping repeatedly...

Even though a bucking may be new, all it needs is a miniscule tear right near that nub to cause a problem... and that often happens during installation if one is not careful or methodic when installing it.  Some of those edges on a barrel can be pretty sharp, and the fit is very tight.

I tried my hardest to "carefully" install the bucking however the crappy hop up and tight bore made this next to impossible... My concave spacer/ nub may have contributed to a tear, ill have to check this out as its seeming more like it could be a problem. As i really had to work it all in there, and the mad bull bucking i got isnt known to be as good as some of their other ones. This is probably where my problem is, ill have to take it out and see tomorrow.

Thank you for your guys help  :mrgreen:

[axisofoil]

As for the nozzle, its possible that i have the "wrong" nozzle. I was unable to determine if the Dboy rifle used a m16a2, m4, or m16a1 style nozzle, to my best ability i decided the gun was over all a clone based on the m4 series, not a m16a2 or m16a1 tm/ca style which take a slightly different nozzle. However i could have been wrong.

My friend probably messed up his shimming when he threw it all together too though... causing the stripping repeatedly...


Thank you for your guys help

Afaik, the nozzles for all of the m4/m16 family of guns are exactly the same.
If the bucking being torn/ripped etc was the problem, you would have little to no accuracy. Catastrophic loss of airseal (missing nozzle, torn bucking, no o-ring on your piston, cracked piston head, broken tappet plate type of stuff) usually causes random power to be generated. Somewhere it might be is in the 'lip' of the bucking... if you had to work it in, the lip may have risen over the barrel enough to no longer make a seal with the nozzle. It would cause a consistent loss of airseal, unlike a torn bucking's normal erratic behavior.

[Comrade Commissar]

The Original Tokoyo Marui style of thinking had different nozzles for the different m16 series actually... SOME of this carried over to a few CA guns, thats why you can buy a nozzle for an m4/m16a2, or for a m16a1/xm177e... There is no difference between m4/m16a2 though, unlike what i said earlier, from what i can tell (ive been looking into it today). Why tm did this, i dont know...

Im going to inspect my bucking, as im sure the nozzle isnt the problem now... returning to my original stock bucking or some systema bucking might fix the problem... The fit of the madbull is just too tight to be able to properly align it all and make sure its in correct. a new hop up might allow me to use it, but im not going to get a $40 hop up to make my $6 bucking work...

[Shadow]

I tried my hardest to "carefully" install the bucking however the crappy hop up and tight bore made this next to impossible... My concave spacer/ nub may have contributed to a tear, ill have to check this out as its seeming more like it could be a problem. As i really had to work it all in there, and the mad bull bucking i got isnt known to be as good as some of their other ones. This is probably where my problem is, ill have to take it out and see tomorrow.

I've got the SCS in my stock hopup unit, and it was a pain to install as well.  A little bit of silicone spray helped me slip the hopup unit onto my Madbull blue bucking without causing it to tear or bunch up.  I put that thing on reeeeally slowly.  I decided to put the SCS nub in last by holding the barrel/hopup upside down.  That seemed to do the trick for me.

[airsoftguy01]

I tried my hardest to "carefully" install the bucking however the crappy hop up and tight bore made this next to impossible... My concave spacer/ nub may have contributed to a tear, ill have to check this out as its seeming more like it could be a problem. As i really had to work it all in there, and the mad bull bucking i got isnt known to be as good as some of their other ones. This is probably where my problem is, ill have to take it out and see tomorrow.

I've got the SCS in my stock hopup unit, and it was a pain to install as well.  A little bit of silicone spray helped me slip the hopup unit onto my Madbull blue bucking without causing it to tear or bunch up.  I put that thing on reeeeally slowly.  I decided to put the SCS nub in last by holding the barrel/hopup upside down.  That seemed to do the trick for me.

When installing a new nub, just take off the gear and cam wheel from the hop up, then rotate the pressure arm out of the housing, put the SCS or nub on, keep it upside down, then rotate it back in, install the barrel with the entire assembly upside down, then install the gear and cam gear.

[Shadow]

When installing a new nub, just take off the gear and cam wheel from the hop up, then rotate the pressure arm out of the housing, put the SCS or nub on, keep it upside down, then rotate it back in, install the barrel with the entire assembly upside down, then install the gear and cam gear.

Yup, that's how I did it.

[CBDennis]

You could just throw in the spring and replace things as they wearout or break.