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L96 Upgrade Problems!

4701 Views 31 Replies 6 Participants Last post by  luke213
Hey guys,

Upgrading my UTG L96 APS-2 has run into a problem: my Angel Custom hop-up unit (which is the exact same as the PDI unit) is causing the gun to totally misfire. The only thing I did not replace is the bucking. When I install the nub and try to fire, I get a dead, flat sound and the BB stays in the gun. I posted a YouTube video to demonstrate the exact problem here:
Without the nub and arms, the gun fires just fine, so I know the bolt system and trigger are all working.

I know lots of people are going to tell me to scrap the AC hop-up unit even though it looks the same as PDI, but there should be a profile difference looking down the barrel with the nub and without it, especially with the gun misfiring. I checked and I can't see any difference. Any suggestions are welcome as I am at a loss for what to do.
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So you are saying the more hop up, the more the arc you are getting?

That is very odd. Is the bucking in there properly? What is your current compression like?
Like is said it might be because you can't apply ENOUGH ho.p You may want to try to put a spacer in between the your hop arm and the piece that pushes on the arm.
Okay, let me try putting more hop on there and maybe I'll get the downward acceleration to zero. Where that happens will probably be a higher trajectory than straight, so I think I may need some drastic scope adjustments to make up for it.

I'm pretty certain the bucking is installed properly. I haven't tested the compression directly; is that the test where you put your finger over the cylinder head? I get really good FPS so far (I don't know exactly how much, but I'm taking this to get chrono'd today.

Does the PDI hop-up take a spacer? I still have no idea where to put it. If I need more hop, though, there's plenty of room to simply adjust it for now.
The fact that your shots are coming out lobbing is puzzling me. Typically, if you are not applying enough hop, the shots will shoot out at a straight trajectory and then drop before reaching desired target. You then adjust the hop up, and bb will reach out further at a straight trajectory before falling. If you apply too much hop, it will go straight, then pull up before reaching desired distance. NOT come out of the barrel at an arced trajectory.

So with that, my thinking is that it has something to do with improper installation. Get that thing chronoed and we can see if there is any drastic difference in FPS variation, and we can go from there. However, I am unsure how much that will help. But its good to get that info and rule some things out.

The PDI hop up takes a nubbin, and is that big long rubber piece. The G&G bucking takes a nubbin that is much smaller. You said you had that installed? Possibly switch out the nubbins, reinstall the bucking, and make sure everything is aligned properly and then go from there.

Lots of times, when I get issues like this, I like to take it all down and reinstall everything in the hop up. Might be a small issue that is not very noticeable. If that does not work, let me know. Be sure to take your time and not rush. Come back with results, and we can go from there.
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So the chrono is at about 380-390 with .28's, but it is very consistent, only about 15 FPS range. Since I have an M170 spring, though, I will have to test the compression. Can you let me know exactly how to do that? I got the main idea but I'm not sure how to do it. I'm pretty sure it's the piston O-ring; I had my doubts about it at first but decided it was probably just intentional that the ring was bigger than the piston and didn't fit on tightly.

The hop-up issue wouldn't really have anything to do with the chrono test though, right? As long as it's consistent the hop-up should do what it's supposed to. The nub that G&G comes with is, I believe, the same size as the one that came with the PDI hop-up unit repair kit, but it is also hollow :)shrug:). When I tear it apart, I will reinstall it with the PDI bucking and see if it helps.

So for now, I will do a compression test and if it comes up failing (it will), I should probably get a PDI piston O-ring? What kind of speed should I be looking for with some different weight ammo (I'm almost out of .28's and I want to try some different ones)?

Edit: I went back to the stock spring, piston and spring guide because I thought I would get better compression on that. I can tell a big difference in the cycling just by the way it behaves. It is too late to test it at all tonight though, so hopefully I will have some good results tomorrow.
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When I can't find a problem, I put the gun back together with all it's stock parts and test shoot it. The problem should stop unless one of the parts you didn't replace is broken. After that you can put in each piece one by one and test fire. This will help you find your problem by the process of elimination.
I've pretty well taken care of most of the problems I had before, now on to new challenges. I can't get the gun to stop jamming every time I try to fire. I'm thinking the primary reason for these jams is a feeding/barrel problem because now the bolt handle doesn't even make it all the way back in the receiver before the BB gets stuck. When I disassembled the hop-up, I noticed that a piece of the bucking was caught between the BB and barrel and the jams since then seem to be bothering the bucking that goes in front of the barrel. What's going wrong inside my rifle?

Another thing, I started looking for some widener barrels just for the sake of possibly wanting one in the future (and as a possible solution to my jamming problem). After some looking around, I found that Evike apparently sells Prometheus widebore barrels (I have no idea if they actually do). Any other suggestions on a widebore?

Evike Prometheus 6.20mm widebore barrel
For the record, I took care of the jamming problem. Hopefully I will have the rifle firing tomorrow and I will be able to sight it in. The problem ended up being that the barrel and hop-up unit were smashing the "lip" of the bucking (the part that goes over the end of the barrel) into the chamber and blocking the BB from entering the barrel. I cut most of it off and that seems to have fixed the jamming problem, although it is too late to test it, really. More tomorrow.
Just a note on your hopup situation before. I've run into buckings that when you apply enough hopup to where it should be rather than raising the bb they drop off. My best guess in these cases is that the bucking isn't providing enough grip to put backspin on the bb and pressure against it is just creating resistance and dropping down the fps as a result. Typically it's been old buckings that have been sitting for ages or just crappy ones that I've seen with that behavior but something to watch out for.

The AC hop-up is sealed with the two O-rings (it's a clone of PDI), so I don't really expect any problems. It may be the piston head that caused the problem because the original AC one I had to change out had worked fine. Also, if the bucking was getting smashed into the chamber, cutting off some of the lip would only cause seal problems if I cut off too much (a real possibility). Eventually I will chrono the rifle and if I see anything interesting I'll keep this updated.

The bucking is a G&G which has a really good reputation and brand new. If you're talking about before I got the AEG bucking, I was using the stock bucking in the new hop-up unit (oops lol).
Just in general I've seen that behavior with a bad bucking. I've got one in an aeg doing that same thing and it's a TM gun with stock bucking but the gun has been sitting for around 8 years till the other day.

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