Odd hopup unit/rubber problem in an AK

[Forever_kaos]

So I recently acquired an AKS-74U and was informed from the get go it had feeding issues.

So whatever, when I got it I tested it and it jammed on the first round.

Now the jam was not too far in the hopup, I could slightly see the BB sitting in the hopup/mag well area.
(Note the hopup unit in the SU is a TM and the rubber is a Guarder clear)

So I decided to break down the hopup unit and see if something there does not look right.

When I tried to remove the inner barrel it was tough as hell, imagine trying to piss out an ice cube. You get the idea, it was crazy hard I thought I was going to break the hopup unit.

So I managed to get it out after a little while, all looked good.

I decided to try my other AK hopup and barrel (both Cyma with Element rubber) and it shot like a dream, all was good.

So I replaced the the TM unit with my Cyma and it now shoots wonderful.

Any idea why the TM unit was causing the gun to jam?

I've used a TM unit before with my current mags and brand of BB's with no issue in another gun (mind you it was a different gun entirely)

Cheers.

[Amos]

Hrm.. possibilities could be;

Hop-up is mis-aligned vertically, so the nozzle isn't going in straight

Spacer is in vertically putting too much pressure on the rubber

Rubber has swollen with silicon oil

What brand is the AK?

[Steven]

AKS-74U would most likely be CYMA, Dboys or VFC. But that doesnt help much :P

[Forever_kaos]

Yep it's a Cyma. Should mention the air nozzle is a Modify

Rubber did not seem swollen to me, that's one of the things I compared.

All in all I'd like to be able to use the TM unit, I enjoyed my last one more then my Cyma, but either way it works and I'm happy. I'm just very curious as to what could cause this.

[Skladfin]

misalignment of the hop up unit due to QC/dimension differences.

[Jonoats]

Really funny you have experienced this problem. My friend has been building up a beast of an SPR over the years and has a Prowin gearbox installed. Now for all who don't know the hopup unit on this type of gearbox is actually a part of the gearbox. For the longest time he was just getting consistent super low velocity shots. I had a look at it with him and fixed up all his seals, seals are good. First shot out of it, 430fps, every shot after that like 200fps. The problem is definitely stemming from how his nozzle is mating with his hopup, so I inspected and changed it. Now however his gun instantly jams. Could it be that too much hopup is now exposed beyond the barrel? Where there was too little before? It was over the holidays and we ran out of time at this point. It definitely seems that the bb's are jamming between the rubber and the nozzle. Any insights would be appreciated, I'm sure when I get back into town and get some more time on it I can fix it, just really an odd problem.

[Forever_kaos]

So after some tinkering around with my hopup units and rubbers,
I have come to the conclusion it is the Guarder clear hopup rubber that is giving me all the jamming problems.

Any idea why? No matter what hopup unit I throw this rubber in it jams up the AK right in the unit.

[Amos]

Care to post a good macro picture of it?

It's hard to diagnose why something's causing a problem from text alone.

[Forever_kaos]

Yep I can do that.
Will get them tonight my batteries have to charge.