Recently I removed the LM4 barrel, and disassembled the hop-up unit to diagnose some issues. It became very clear when it was disassembled down to the bucking cover that there's something really wrong. Rather than return to the off position the hop up remained protruding into the barrel. In an effort to adjust the hop-up by pressing down where the tensioner should be, it simply protrudes into the barrel 100% with a rapid pop, or remains completely off. It does not take well to pressure being gradually applied. I previously thought the fins were torn slightly, but the two nubs actually where simply resting inside the barrel at an angle of approximately 20 degrees. I noticed a slight tilt of the fins from factory, very small but just barely noticeable to the eye. Also I found that the bucking has a substantial chunk missing out of the bottom lip near the feed ramp. The bucking also does not firmly rest on the barrel, it seems like it has swollen and become loose.
What I need to know is how to prevent something like this from happening with a new bucking. Perhaps it got too much lube and became malformed and swollen? And what could could have caused chunks to get torn off of the bucking? I can upload pictures to better convey what I'm saying, if necessary.
The compression still drops and does bb rolls, like it would with a worn out stock piston o-ring. I think the bucking is the culprit. I've replaced the o-ring to the Harbor Freight one as Boobie suggested, and lubing everything generously helpd the cause slightly, but not for more than a magazine. Is there any trouble shooting that can be done other than just buying a new bucking? I wouldn't want the same thing to happen again, or fail to find the elusive solution to this compression loss problem.
Edited by Jatodude, 02 May 2013 - 04:34 PM.