View Full Version : Possible to exchange CA hop-up for Systema?

09-09-2004, 08:53 PM
I need information about the swapability of the Classic Army metal hop-up for the Systema hop-up. I began to have some problems with my hop-up after having my Classic Army M15A4 for about a month.(bbs dropping to the ground after traveling only 40-50 feet) A simple hop adjustment corrected this problem. But after a week or so the problem returned. This happened more and more frequently. I thought the screw that presses against the main hop adjustment gear had loosened up but after checking, I found it to be very snug. At this point I removed and inspected the metal hop-up assembly and found that the little rubber "nub" that presses against the hop bucking had become very hard, brittle, and partially collapsed on one side. I then replaced the hop bucking and the little nub. "Voila" I said. Wrong! Now the hop works perfectly, but backs its self off after firing a few rounds. The small plastic gears seem to have loosened up due to me disassembling the hop-up mechanism, and will no longer stay "set". So, I did some research and discovered that others have experienced the same trouble. It seems to me that the Classic Army hop-up is almost an exact copy of the Systema hop-up. I was wondering if this is truly the case. The consensus seems to be that the Systema part is superior to the Classic Army. I need to know if this is truly a drop-in replacement, as I do not wish to cut away metal portions of my rifle to get it to work.

09-09-2004, 11:18 PM
No, the CA is a copy of the Marui hop up, so you would have to cut the lower receiver to make the Systema one piece hop up fit. If it is constantly backing out, and the screw on the gear that you turn to adjust the hop up is tight (ie you can't snug it up any further) there are some things you can do to help.

1: Use some plastic safe loctite between the screw and the gear.
2: Put a washer on top of the gear that will press down on the gear when the screw is installed.
3: Put a little RTV on the gears 'axle'.

All these will make the mechanism a little more vibration proof.

09-10-2004, 09:03 AM
Thank you for letting me know that the Systema part is not a easy fit.I will try your suggestions first. Tell me, what is "RTV" exactly?

09-10-2004, 09:25 AM
Related info: http://www.dragonairsoft.org/jballou/tut-systemahop.php

RTV is silicone adhesive. Try a small amount of Loctite first on that screw, as that is usually enough to do the trick. That screw should have a washer on it aleady or at least a large head that serves the same purpose, but it wouldn't surprise me if CA left that out.