"Given the good ratings this has gotten, I had high expectations.
I have a CYMA CM042-S AK47S.
I bought a Matrix 3000 Magnum High Torque motor to use with this, which, given its reviews, should have been more than enough. I got everything set up, but the motor couldn't pull it back all the way, and the gears just locked, and the fuse blew. Eventually, after MUCH messing around, buying of different parts, etc., I decided to do some testing, and realized that this spring, when compressed fully, is still too long to allow the gun to fire. aka, the distance the spring is completely compressed, so the coils are smashed up against each other, it would have needed to have been compressed further than that to release, which is not possible.
All told, this problem caused:
* Two full sets of destroyed gears: the stock set, and a new Matrix High Torque set, along with the stock pinion gear
* Broken stock piston
* Warped gearbox
* Innumerable wasted shim jobs
* About 5 blown fuses
I'm very disappointed, as I thought that this spring would fit virtually any AEG, especially something as mainstream as a CYMA AK47. However, it is too long and has too long of a solid compression length, rendering it useless.
"I just used this spring a few days ago as I just had it installed in my SR25, it shot on average, 350fps. All day as I was playing there were no problems with it. A very good spring by Matrix.
"I bought this spring about 8 months ago to go into my JG SIG 550. The FPS on the first chrono I used was 395 FPS with .25g BBking bbs. Went to my first Milsim this year and I chronographed it there and it was shooting around 429 FPS with .25g Elite Force bio bbs which I don't like. So needless to say I had to take my gun apart and cut 4 coils off to get it down to 390 FPS with .25g bbs. I don't think this has anything to do with the spring I think it was the chronographs I used and bbs, BB King bbs are better quality bbs than Elite Force bbs.
Note: I have a bearing on the piston head and the spring guide which compresses the spring more which in turn can increase the FPS. Plus I have 100% air seal and a type 0 cylinder.
Overall I think this is a great spring! I think next time i am getting a Matrix M113 irregular pitch spring.