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PDI hop up adjustment screws

17405 Views 125 Replies 13 Participants Last post by  fuzzywolly
Ok, so today I decided to tweak with my rifle and installed the PCS (polar star concave spacer). I took out the pdi nubbin as I wanted to try out my pcs due to problems I was having with my hop up.

Turns out the problem is not so much the nubbin I am using, but its the screws themselves.

You see, after I adjust the hop up screws to that sweet spot it goes something like this....

-First shot: Straight, dead on, just beautiful.
-Second shot: Same as the first
-Third shot: Way right
-Fourth shot plus rest of shots: Way right

I could not figure out the problem for quite some time, and after around 2,000 bbs put through it, I think I figured it out.

I realized that when I would adjust the screws, it was way to easy, and the screws seemed loose. They would turn with just the slightest force. This brought me to the conclusion, that after a few shots, the vibration from the rifle, causes the screws to turn themselves, readjusting the hop up.

I am thinking about trying some screw tightner substance that keeps the screws from loosening up so easily. I will still be able to adjust them, but it will take alittle more force.

I want to run out to home depot or true value today, but I wanted to know what kind of screw tightner you would recommend. Keep in mind I do not want it to be too hard to adjust, just something to keep it from loosening up so easily.


121 - 126 of 126 Posts
awagg said:
Tried the spring thing yet?
As in a new spring? I have already figured out that was not the problem.

If you are referring to something else, let me know.
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awagg said:
Fuzzy, I'd try that first idea... get some spring guide spacers. The problem could be that the spring might be loose at resting position, and can get a little tweaked when pulling the bolt, giving you bad consistency.

Since, usually, when there is a problem, like a burr on the piston, it consistently shoots like crap, but in the SAME DIRECTION. Your problem seems like it's super random... a spring twist could be the case.

Try this: first, pull your bolt back really herky-jerky. Try and get the spring to freak out. Then try and pull it in a nice, fluid motion, and see if your groupings improve.
Thanks awagg, I will give that a try and see what happens.

On another note, HP chamber arrived today. Will snap a few pics, and then assemble and test fire the rifle. Updates on HP chamber will be in the other thread known as HP Chambers...
awagg said:
Ever get this thing to work?
The HP chamber came earlier than I thought and decided to work with that. Never got to try the PDI again and see if the spring was the issue.

I did get a few test shots with the HP and it is shooting relatively fine. Therefore, I believe the spring is not the problem. More updates will be to come, just having a tough time finding some good weather to shoot in.
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