Xaccers Posted June 29, 2007 Report Share Posted June 29, 2007 A mate's CA M15 jammed and started making crackling noises from the motor a while back. I stripped it down to find the motor burnt out, and the front of the gearbox cracked (gotta love them V2 boxes) So, ordered a replacement gearbox, fitted everything across, and found the middle gear on the hop unit had a broken tooth and the gun was firing at only 200fps (stock spring) So ordered new hop unit and replaced the broken gear. Still only 200fps. Bunged in a M110 I had spare. 180fps! Back to stock spring and it's doing 200fps again. Noticed the nozzle looked a little dented, so ordered an airseal one. Now the gun's doing 250-260fps with M100. Took another CA15 and swapped upper recievers. Both do over 300 fps. So, the upper reciever on another lower reciever is doing over 300fps The lower reciever on another upper reciever is doing over 300fps Lower and upper together doing 250-260fps. It's 1am, I'm tired, my right eyelid is twitching, anyone got any ideas? Link to post Share on other sites
Tommygunn Posted June 30, 2007 Report Share Posted June 30, 2007 Looking in the magwell, is the hop unit butted up against the front of the gearbox i.e. touching? Link to post Share on other sites
Xaccers Posted June 30, 2007 Author Report Share Posted June 30, 2007 As far as I can see yes. Going to chrono it later with just the hop/barrel and lower receiver to see if I can find the bloody air leak. Link to post Share on other sites
Noodle_2000 Posted June 30, 2007 Report Share Posted June 30, 2007 Possibly air leak. Check your compression whenever you open the Gearbox again. Check your cylinder head, I've had a defective CA before. Also if I might make a suggestion, you might want to go ahead and do this since you have everything opened. It should help out in the long run. http://www.airsoftretreat.com/forums/index.php?topic=40038.0 Gary B. Link to post Share on other sites
AGuy Posted June 30, 2007 Report Share Posted June 30, 2007 double check to make sure air isnt coming out of your magwell when you fire (something wron with air nozzle) Link to post Share on other sites
Miker Posted June 30, 2007 Report Share Posted June 30, 2007 air leak... Could the o-ring around the cylinder be cracked in any places? Link to post Share on other sites
Tommygunn Posted June 30, 2007 Report Share Posted June 30, 2007 The above link is a similar idea to what I did, except I used a small block of leather. Link to post Share on other sites
Shard Posted June 30, 2007 Report Share Posted June 30, 2007 Yup, I found a similar problem happened with mine, and did something alike to that leather spacer with some card. The spring on the CA hop unit is pretty poor at pushing the hop unit tightly against the air nozzle, so you lose power as a result. I had this issue myself, and a friend with a tac carb also had it. In the end I replaced the hop unit in it's entirity, and got a much better fps reading off the same gearbox. (280 vs 320) Link to post Share on other sites
Xaccers Posted June 30, 2007 Author Report Share Posted June 30, 2007 I cheated. Swapped the barrels over with the other gun, and now both are doing 300fps. Definitely an airleak somewhere, most likely the hop chamber, cylinder compression is great. Like the idea of the o-rings rather than the spring, thanks for the link Link to post Share on other sites
MDK_Marshal Posted June 30, 2007 Report Share Posted June 30, 2007 It may even be a bent barrel... I've encountered this before, I had an M15 in for something (can't remember what) and couldn't for the life of me get it to chrono over 300. Swapped the upper receiver over and voila, it was firing at about 380, IIRC. outer barrel was a bit bent, pressing on the inner and slowing the BB down quite a lot.Gun was re-tuned to 350, and its been working fine ever since... Link to post Share on other sites
Xaccers Posted June 30, 2007 Author Report Share Posted June 30, 2007 Funny you should say that, the slow barrel is able to move in and out on it's spring freely, the fast barrel isn't, it feels a bit stuck in it's grooves Link to post Share on other sites
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