Upgrading a CA SA58 to 390fps.

[Parafal]

Maybe somebody can help.

My friend has a CA SA58 AEG. The original FPS was 320.
He wants to get 390fps.

He tried with a SYSTEMA M120S spring and got only 350fps. He tried a M140 spring and the motor couldn't handle it.

Any idea what is happening and what he should do to get his 390fps out of his SA58? Change the motor?

Some pictures:

[Styrak]

Don't use a silent head set, those can lower your FPS.
Also, if you're using a mini battery it wouldn't be able to crank an M140. If you're using a large battery, then it's not working because Classic Army motors are crap. "High torque" my ass. They've never impressed me, stock TM motors are better.

[theguy]

M120 should give you more then 350 FPS. Hows your air-seal? That would be my guess

[Skruface]

Motor will have no effect on your FPS. There could be several problems. I would check them out in this order:

1. You could have the spring in backwards. Yes, it does make a difference.
Test 1: Swap the spring around and testfire. If there is no change, move on down this list.

2. Piston head-to-cylinder airseal issues: This piston head could be out-of-round, causing an air leak, or the piston head o-ring could be too tight, not creating a good seal between the piston head and the cylinder wall. Alternately, the cylinder itself could be out of round, allowing for a gap between the piston head and cylinder wall - this usually occurs when someone inexperienced opens their mechbox for the very first time, and tries to screw it back together when the cylinder is not seated properly, warping the cylinder.

3. Cylinder-to-cylinder head airseal issues: The o-rings on the cylinder head could be too tight, allowing air to blow past the cylinder head. Or, the cylinder head could be out-of-round and not seating properly in the cylinder.

Test for 2 & 3: You assemble the cylinder head, cylinder, piston head and piston outside the mechbox. Put your finger over the hole on the shaft of the cylinder, and press the piston in. If the piston moved easily, you have a compression problem. If it's difficult to push the piston in, your compression is good.
Repair: Replace o-rings with slightly larger ones (or soak old ones in 100% silicone and stretch them by putting them over the cylinder overnight); retest. If you fail again, take a closer look at the piston head and the cylinder head; either (or both) may need replacing.


4. Cylinder head-to-nozzle airseal issues: The nozzle could be too loose on the shaft of the cylinder head, allowing air to blow out around the nozzle, instead of through it. Check to see if there is a o-ring on the inside of the nozzle that may be missing (could have blown out through the barrel).
Test 4: If Test 2 & 3 shows a good airseal, put the nozzle on the shaft of the cylinder head and repeat the test, with your finger over the hole in the nozzle and pushing in the piston. If the piston moves in easily, this is the problem.
Repair: Replace o-ring in nozzle if missing; if nozzle is of the type without an o-ring, replace with an o-ring nozzle (I would suggest a Modify nozzle with o-ring).

5. Nozzle-to-hopup airseal issues: Sometimes the nozzle sits too loose in the hopup unit, causing air
leaks. This could be a problem with the nozzle's outer diamater being too small, or the inner diameter of the hopup chamber being too large. I commonly find this issue in guns made of mix-n-match parts from different companies.

6. Torn or ill-fitting hopup rubber: If there's a tear in the hopup rubber, you will lose compression causing a loss in FPS. Also, make sure the small brass ring that centers the barrel within the hopup unit is present; some people lose these and assume they aren't important.

Test for 5 & 6: Remove hopup assembly and inner barrel as one unit, and also nozzle. Fill a small pail with water. Insert nozzle into hopup unit, and place on finger over the bb feed hole and one over the back end of the nozzle. Submerge the hopup end (keeping nozzle and bb feed hole sealed with fingers) in the water and blow gently into the muzzle end of the barrel. If you see bubbles at the back end of the hopup, the problem is with the nozzle/hopup interface; if the bubbles come from around the hopup rubber, the rubber is the issue.
Repair: Replace damaged part(s).

Note that if you have done all of the above and not found an airleak, you may just have a bunked spring. It happens. Try a different spring.

Good luck.

[Parafal]

Thanks guys for the infos.

I'll send him these informations.