Introduction: Airsoft Pistol Mod. CYMA P.638

Picture of Airsoft Pistol Mod. CYMA P.638

Here is a air soft modification that is simple and will increase the muzzle velocity. The gains are moderate but if you have to disassemble your CYMA or similar air soft pistol any way, this Instructable will help make your gun a little better.
I bought this pistol for under 10 bucks and was surprised at it's accuracy at short distances. Surprised a few squirrels and other vermin with it. I being cheap also put some mini paint ball ammo through this CYMA P.638. Bad idea! The paint ball ruptured in the breech gummed it all up. Now I have to take it apart and clean it, so here we go..

Step 1: Disassembly

Picture of Disassembly

First we must take it apart. The arrows in the photo show where the screws are that hold it together. The orange outer barrel cover is glued on so be careful don't try to force it off or apart.
This modification will use one flat washer 1/2"diameter or 13mm., and one 7/16" nut. Utlilizing the original spring but increasing it's compressed energy so it will release more energy when it expands. See photos below.

Step 2: Modification

Picture of Modification

Remove the cocking barrel cover and you will see a spring over the barrel and the orange cap on the end of the barrel, this spring slides off the barrel when you separate the two upper halves of the barrel. You will also see a movable piece with a spring behind it. This is the part we are interested in. Pull back on this part and lift up to remove. Hold on tight as you have to compress the shorter spring to remove it.
The photo shows the three pieces that make up the pneumatic part of the pistol. The spring, piston , and compression tube/ breech loader. careful with the compression tube and piston as a tear in the rubber seal on the piston ,or scratch on the inside of the tube will effect muzzle velocity.
The stock length of these three parts together is 94mm. By adding the nut and washer to the inside of the piston we increase the length by 6mm, so are parts together now are 100 mm.
The 6mm is all I could add without making more mods.
Now put the 7/16" nut in the piston and the washer on top of nut so the spring has a flat surface to rest on. Put the piston in the tube, you could give it a few drops of pellet gun oil too. Put the spring in the piston and WHALA! It's done.
What we are doing here is using the nut and washer to effectively shorten the compressed spring, making it release more energy as it expands when you pull the trigger.

Step 3: Cleaning Barrel

Picture of Cleaning Barrel

Before we put it back together it would be a good time to clean the barrel and breech areas. As I mentioned before I had some mini paint balls explode in the breech. To remove the barrel it is necessary to separate the two gun halves. Remove all screws except the one nearest the compression spring support, just loosen that one. Spread the gun apart enough to slide the barrel assembly off of the pin that holds it in place. Take note of all the parts that stay in the halves as you open it, if the trigger should fall out or something else becomes dislodged you will know where they go.
The barrel assembly consists of an outer and inner ( the real barrel). On the end of the real barrel is a rubber seal, it serves two purposes 1. to seal the compression tube to the barrel and 2. to hold the 6mm airsoft pellet in place until you pull the trigger.
One screw holds the breech end of the barrel together, and that bloody glued on orange cap on the other. Don't try to remove it, just take out the screw and spread it apart, the real barrel will come out with a little work. Take the rubber off and clean the inside of the barrel with alcohol and cotton swab. Look down the barrel to make sure it is all clean. You might notice some bumps in there, don't try to remove those just any build up inside barrel. Those bumps are to encourage the pellet to back spin when leaving the muzzle. Not all barrels have this.
As an extra insurance against any compressed air escaping from the seal and barrel I put a SMALL amount of RTV silicone around the outside of the barrel where the seal will set. Make sure there is no RTV inside the barrel and put the seal back on. Run your finger around the seal where it meets the barrel and remove excess RTV.
Put the barrel back in the outer barrel, make sure the inner barrel is all the way in before replacing screw.

Step 4: Reassembly

Picture of Reassembly

Spread the gun halves apart and slide barrel assembly back on pin. Put all the screws back that hold the pistol together.
We will also add two new screws to strengthen the barrel assembly in the lower part of the gun. This is not necessary but I did it because of the added spring pressure and energy release that the pin will endure with this mod.
Drill a small hole through the lower part of the gun into the barrel assembly, not much room so be careful. Screw into these holes screws a little larger than the holes. they should be a wood or sheet metal threaded screw with a point.
Put the smaller spring , the piston and compression tube back in the pistol. The nut and washer are inside the piston, with the spring against the washer.
At this point lets make sure this will work, pull back on the compression tube until the piston with its latching boss engages the trigger latch mechanism, the piston will stay back and the compression tube is free to move forward against the barrel assembly. IF it does not latch then the added nut and bolt are too thick. 6MM( nut and washer) was the most I was able to get it there and have it latch correctly.
Now hold the compression tube TIGHTLY, using a downward force and pull the trigger. Hold on to it and let it come to rest against barrel assembly. IT is a strong spring and its under more pressure now with this mod. BE CAREFUL.
Slide the bigger cocking spring over the barrel ass. and replace the upper cocking part of the pistol halves and your completely done.
Have fun and wear appropriate protection in what ever you do.
I am working on vids before and after, so you can see the improvements.


olmon (author)2012-09-10

I grew up using Daisy Red Ryder lever action BB guns for what you are doing & those old Daisys shot so slow that you could watch the BB go, but they still stung to get hit by.

AnarchistAsian (author)2008-12-13

CYMA SUCKS!!!!!!!!!!!

the aks are decent, especially for beginners

they've started coming out with Tokyo Mauri clones that are very good

oh yeah, what gun do you have? mines a G&G; combat machine m4

a Team SD M14 spring, 400 fps

mines around 360fps but Im okay with it since it still shoots very far and accurate

electric or spring?

electric, and it shoots around 15rounds per sec. with an intellect 8.4v 1600mah battery

how much did it cost?

wow this conversation lasted many months lol

jeremy91511 (author)spartan 22092010-05-03


Matt21497 (author)AnarchistAsian2009-05-29

i ahve the same gun the red dot site it comes with is very inacurate and all around its pretty inacurate even with .25s! but its strong for backyard wars wich is all i need and i can snipe sorta

murdm3n (author)Matt214972009-06-07

wow that gun sucks my............ i have jg 614 that shoots 415 fps

AnarchistAsian (author)murdm3n2009-06-12

the m14 costs 30 dollars and shoots 400 fps, soo....

murdm3n (author)AnarchistAsian2009-06-12

sorry to tell u, but i bet it definitely is not 400 fps.. have it cronned and send me a pic when it is cronned. :)

AnarchistAsian (author)murdm3n2009-06-16

here it says 380 with a .12, and it's crono'd, but if you lubricate the barrel, it goes almost 500

murdm3n (author)AnarchistAsian2009-06-17

NO WAY IN HELL that gun will ever hit 500 even if u get a new spring... i have it (as one of the first guns) what do u mean "lubricate the barrel"...

spartan 2209 (author)murdm3n2009-08-24

he said "almost"

murdm3n (author)spartan 22092009-08-25

dude dont comment... i have the gun... and the max it goes is 300-350

spartan 2209 (author)murdm3n2009-09-12

You have a chrono? Oh ok my bad. Because if you just had the gun there would be NO way of knowing.

murdm3n (author)spartan 22092009-09-12

lol.. i have 3 different airsoft guns and my bros have another 2. they each go different speeds.

spartan 2209 (author)murdm3n2009-09-14

Are you slow or something? what does that have anything to do with the comment I posted? Gun descriptions aren't reliable sources for FPS, either you have it verified by a chrono, or youdon't know the FPS. Thats it.

AnarchistAsian (author)murdm3n2009-06-18

you don't know what lubricating means? as in put lubricant in it? less friction in the barrel means the bb goes faster...

murdm3n (author)AnarchistAsian2009-08-02

it will stick the barrel up

AnarchistAsian (author)murdm3n2009-08-03

um... no it won't...

murdm3n (author)AnarchistAsian2009-08-08

lol... it will.. wat did u use?

AnarchistAsian (author)murdm3n2009-08-11

airsoft lubricant.... it doesn't get any clearer than that... have you ever even used the right kind?

murdm3n (author)AnarchistAsian2009-08-11

LIKE: WD40. wat did u use? they sell airsoft lub?

AnarchistAsian (author)murdm3n2009-08-22

airsoft lubricant... are you slow or something? no offense...

Matt21497 (author)murdm3n2009-06-08

well we dont want really strong guns that hurt to bad and my moneys tight so it would be nice to have a better gun but for now this is good enough and besides i just started

murdm3n (author)Matt214972009-06-08

isnt that the point of the game? hurt the opponent? 415 fps leaves a welt from about 20-50 feet. the closer you are the more painful it gets. but you will get better because then your trying not get hit. my gun was 150-170 dollars. i had like 3 cruddy guns before and it is so much easier to have a durable and more expensive gun.

Matt21497 (author)murdm3n2009-06-09

i know and for where we play most of our guns our good but we just play in backyards or just shoot targets so it dont matter to much and i want another airsoft gun but my parents wont let me get one for a long time

murdm3n (author)Matt214972009-06-09

yeah at first i couldnt get a gun... took a while. i play with a couple friends we all have decent guns.

jakee117 (author)AnarchistAsian2009-03-16

Their aks are decent... i have an e1 g36c and hope to get a KWA NS2 usp compact for my birthday april 17th...

bustedit (author)2009-09-14

on the box it says "last selecting". does that mean this gun is the bottom of the barell, quality wise, as in "last picked"? the translation on some of those airsoft gun boxes are a riot.

rambler4 (author)bustedit2010-02-07

Not sure sir, the translations are quite entertaining some times. Sorry for the delay.

silencekilla (author)2009-06-25

for the record you never wanna use airsoft paintballs in a spring airsoft gun only use them in co2 and green gas guns if you get paint stuck in you gun private message me and i will post an instructable on how to get it out in less than 5 minutes and with out taking the gun appart

Outfielder1896 (author)2009-05-28

Great im pretty into airsoft and i needed something for my sidearm. I cant choot people close range with an l96 sniper rifle that i modded for 600 fps, so this will help a bunch.

lincalfaiz (author)2009-02-06

Hi there....i just discovered the interesting world of airsoft. I have a Jieke Edge P288G "air pistol". Can anybody out there tell me if this is a "reasonable" gun,pls? I've mod my gun according to rambler4's technique and it's slightly more powerful now...just wondering if there's anything else i can do to it. Appreciate some suggestions here,pls. TQ!!!

Geemo5 (author)lincalfaiz2009-04-28

actually all you need to do to practically double the power is take the small spring ( not the cocking spring) out and stretch it. i did it to my gamo and it works good as. (excuse my english im from new zealand.)

avwos (author)Geemo52009-05-16

No, you should never do that. It may make it more powerful at first, but it will slowly destroy your spring. It can even half the power of your gun after a month or two.

Trid (author)2009-01-23

Brilliant! I think I may do this.

tomcat955 (author)2009-01-23

to much time on his hands

stephenniall (author)2009-01-20

Hi lol i just bought my first real bb gun a cyma p - 918 says 200 fps its quite good Im gonna do this nice mod

Landon Sullivan (author)2008-12-02

Nice, the way I see it, you could do this to any springer. or some electrics, for that matter.

rokor (author)Landon Sullivan2008-12-04

I did this to my Crosman Mp5 1 or 2 years ago and it was very much worth it. Along with a few other mods, got the FPS up to 295.

tater killer (author)rokor2008-12-09

what was the original fps

rambler4 (author)tater killer2008-12-09

Not sure ,but I think it was about 180 fps. I do know it shoots farther, straighter and it stings more. Probably closer to 200 fps.

rambler4 (author)rokor2008-12-04

Thanks y'all for looking at my Instructable, and leaving comment. Rolor, what were the other mods. you did to get fps up to 295?

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Bio: The best things in life are dangerous.
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