KJW M4 GBBR Hop up from hell.

[Olisharpeye]

This is my first Gas Blow Back Rifle, And I love it. Just want it to shoot straight

I've what seems to be the hop up unit from hell. I have dismantled and looked into every aspect but I am completely blind sided to seeing this problem. I've recently modified the gun with the "Top Dead Center" TDC Hop up Mod. And from the looks of others I've seen to do it correctly. The set screw pushing down on the end of the hop up arm.

`But the tighter I make the screw, the worse the hop up becomes. After I've reached a certain point, ;sorry can't exactly measure. The Bb's will just roll out, like if there was no hop up. But I'm quite certain there should be a substantial amount of hop up on. If I loosen the screw all the way bb's will fall short probably within 40 feet to add as well no bb's will fall out.

I will sometimes get the perfect shot maybe 1 or two times in a row, but than it will go crazy and shoot one to the moon, than another to ground. It cycles like thing all the time.

I still got the original hop up unit installed, and I can't get it to work with hoping .3 bb's. (Madbull Bb's BAD?!)

Things that may have lead to bad accuracy that I think I have covered. But maybe I did something wrong.

1) I had a really dirty barrel, Unfortunately I've broken two cleaning rods, so I used some silicon oil weight 10 and a lot of micro fiber cloth strips.

2) Gas Compression, When I opened up the bolt carrier, I've noticed my Cradle piston cup was gunked up and loose. Stripped the grease and re tighten the screw, put some blue lock tight on it put it back together and added some more lubrication.

3) For a while, I had a friend who told me the hop up unit went one way, But I think hop up arm was installed incorrectly. I'll do my best to describe this in words. On the hop up arm, there is a little bump on one side. I had that bump seated in the spring. Ever since than, I've never been able to turn the hop up dial, thinking somehow I managed to break it. But when I reversed the hop up arm so the bump is no longer seated in the spring but now under the hop wheel, so wheel turns while raising and lowering the hop up arm. So it's possible I've some how damaged this unit when it was installed incorrectly. I've checked the rubber for tears and did not find anything.

This hop up has driven me one step before insanity, I appreciate any and all help. If you tell me to repeat something, I will certainly do it! I will do anything at this point in time. I'm very desperate to have this working!

Thank-you. Oliver B.

[NVC]

The bump on the hopup arm is suppose to sit under the hopup wheel adjustment. So when you turn your hopup wheel that bump on the hopup arm makes the clicking adjustment sound. If you put that bump on the hopup arm into the spring you have it upside down. With the grub screw mod you need to do micro adjustments for the hopup. Start with the hopup off. Then do tiny micro adjustments till you get the desired hop. If you turn too much you will get BB jams. Are you using the the blue Ra-tech hopup rubber or the stock black one? The Ra-tech rubber has better BB contact then crappy black one. If your not shooting straight make sure your inner barrel and hopup unit is straight and locked in the outer barrel. Dissemble and clean your inner barrel and hopup rubber with warm dish soap, not silicone. Try a different bb brand and chrono your gun to see your shot to shot fps consistency.

[Olisharpeye]

Excellent, I'm glad I at least figured the hop up unit correctly! As for the hop up unit it is stock black rubber. I will get on warm dish soap and water method for the inner and hop up unit and hopefully come back with some positive results. As well as check for barrel stability inside the outer barrel. I will follow your wise advice to the letter. Thank-you I will post my results.