BB not entering into the barrel
 

I recently changed the spring in my CA M15A4 RIS to a stronger one. The gun was dissembled and reassembled back to its original condition.

However, this problem happens when I test the gun. The gun fires, but no BB comes out.

I checked piston/cylinder assembly, air nozzle, hopup, and magazine feed. The gun is definitely firing with no or minor air leak, but BB just gets stuck at the entrance to the inner barrel, not being able to travel down.

Occasionally, one or two BBs come out by surprise.

Could anyone kindly help me on this strange problem? I do not wish to damage the gun further if I do not know what has been happening.

Thank you very much for your time. I would really appreciate it.

What hopup sleeve are you using? Sometimes the entry lip around the sleeve is too long/soft. Instead of letting BBs push past it, it will instead get in the way, bind and jam the BB at the mouth of the inner barrel.

Is the air nozzle correctly mounted onto the end of the tappet plate? I had exactly that problem with one of my guns a couple of months ago. When I reassembled it, the nozzle came off the tappet plate. The gun cycled fine, but nothing would fire. If I pointed the barrel upwards before shooting (causing the nozzle to move back and allow a BB to feed), I would then get the odd single or double feed.

If the hopup unit wasn't changed in any way, I wouldn't look there as the first source of the problem.

Pop the BB out using a rod or something, put two drops of silicon oil into the loading tube of your hop up unit (where the BBs go), dry fire on burst a few times, start shooting again. Simple fix, lack of maintainance issue.

Buffer tube screw is screwed tight. Try to loosen it a bit but if it does not solve the issue pm me at op-for boards.

What? if you put any lube inside or in front of the hop up rubber, or any where that it may transfer to the rubber, the bbs will slide past, and not get the proper spin.

Are you by any chance using a too tight inner barrel?
Check the faulty bb's the other way, through the exiting way, do they go through?
Remember, some barrels go as tight as 6.01mm (I've even heard 6.00 but that would be a very tight for use barrel), but the bb's can vary with +/- 0.02 mm. Try finding some high quality bb's, small amount, just for testing.

No, it needs to be oiled once in a while (check the manuals, they suggest silicon oil spray every once in a while). Once you get the oil in there, yo uhave to run a mag or two through the gun to get the bulk of the oil off the rubber to have the hop up work properly. That is all standard procedure. If you don't ever lube that area, and allow the hop up rubber to get tacky, then BBs will refuse to get pressed through the breech part of the rubber and the above (plugging) is exactly what happens. I've fixed dozens of guns (including on the field) that plugged up, by putting a couple drops of oil in, and every single one of them ran the rest of the day without a burp.

broken tappet plate perhaps? with eye protection on and an empty weapon,,turn it upside down and dry fire it once or twice while looking into the feed tube. if you see nothing moving during the dry fire,,your tappet plate is broken.

I have this rubber re-conditioner that i use for my hop up, i apply it, then let it sit over night, and i just need to wipe out the excess and it works just like new and i only need to do it at the start of the summer, and maby once after the winter if i played then too.

I found that with applying any oil/lube to the hop up can make it slip, and move, possibly making the bbs curve to one side.

Like C Stalk said turn hop up off, flip gun upside down add 4-5 drops of oil through the feed tube of the hop up, dry fire 2-4 times, than run a 200 round hi-cap through, while increasing the hop up, this will fix your problem most likely. Than clean the barrel once everything is feeding properly.

The oil that dosent absorb into the rubber will dissipate as the gun is fired, so the first 200rounds will be wild or act like there is no hop up, you may even need to burn 400rounds.

yea, with my way, you don't need to run though so many rounds, but i might use it when im at the field and cant let it sit over night,

Thank you all very much for your generous and kind help. I sincerely apologize that I have been too busy with lab research work and could not send my thanks earlier.

Yes, the problem is finally solved by cleaning the gun and re-positioning the tappet plate properly. As six4 said, the tappet plate was not moving when I used his suggestion to examine the gun. It was positioned incorrectly that it could not move properly. Adding silicon oil also helped and the gun is running smoothly again.

Thank you all again. I really appreciate your precious assistance.