ISSC classic Army MK16 power issue

[Rm1980]

Afternoon all,

I acquired this weapon a while back. The seals have been replaced, gearbox is fine, MOSFET is working but it only hits 43fps.

I am now looking at replacing the barrel and hop unit but I don't know which of said items to buy as this would be my first time upgrading. A pointer in the right direction would be highly appreciated or a suggestion on what else could be wrong as well.

Regards, Red

 

[colinjallen]

If you really are certain that everything in the gearbox is ok, then it would seem that you have a truly massive air leak between the nozzle and the hop rubber; you can check this in two ways:

1. After checking there are no BBs in the hop, turn the gun upside down and place a small piece of paper covering the open end of the feed tube; if the piece of paper flips up or levitates, you have found the leak.  It could be that the wrong nozzle has been fitted, that the nozzle is worn or that the hop rubber feed lips are damaged.  It could also be that the nozzle is not coming forward fully, which would be a gearbox issue.

2. With the nozzle, shine a light up the feed tube and take a look down the barrel; if you can see light, see above.

If the stock hop unit is the rotary one, I would not change it; it is rather good.  However, consider fitting a Maple Leaf Macaron rubber and one of AK2M4's 70 shore Omega nubs.

For the barrel, I would recommend one of the ZCI ones; once again, AK2M4 sells them.

If you haven't already done so, fit a good quality high torque motor.

 

[Rm1980]

@colinjallen Thank you for your answer. From the time is wrote the post above and reading your answer, I stripped the gun again. Looking down the barrel and the hop fully open or closed, bb's just fall through. After adding a piece of foam to the hop (just as an experiment), I finally could see a lip forming on the bucking. Reassembled the gun (at this point I could not get the fire selector in place and it's full auto all the time), and did a test fire. My hobby room is 4 sqm, and I didn't even hit the wall.... 

Tomorrow, I'll run strip it again and follow your instructions. When you say feed tube, you do mean the opening of the hop unit, correct? In regards to the hop unit, I have attached a picture of it.

View attachment 88451

 

[colinjallen]

Yes, that is the rotary hop unit.  The feed tube is the one at the bottom through which the BB's feed up from the magazine.

You don't need to take the gearbox out to remove the hop unit and barrel or to do the tests that I mentioned.  Does the hop unit have an arm similar to the one circled in the photo (this is not the CA Scar chamber) or is it missing? There should be a rubber nub at the end of that arm that presses down on the hop rubber.  There should also be a narrow spring on the lug on the top right of your hop chamber; this helps to push the chamber firmly against the gearbox.

 

View attachment 88468

 

[Rm1980]

Yes, that is the rotary hop unit.  The feed tube is the one at the bottom through which the BB's feed up from the magazine.

You don't need to take the gearbox out to remove the hop unit and barrel or to do the tests that I mentioned.  Does the hop unit have an arm similar to the one circled in the photo (this is not the CA Scar chamber) or is it missing? There should be a rubber nub at the end of that arm that presses down on the hop rubber.  There should also be a narrow spring on the lug on the top right of your hop chamber; this helps to push the chamber firmly against the gearbox.

 

View attachment 88468

It has the arm but nothing else.

Spring wise.. there is a spring on the front and its a tiny little thing.

I ordered the bucking and nub. Should be here tomorrow. I assume without the nub I cannot really test for air leak?

 

[colinjallen]

It has the arm but nothing else.

Spring wise.. there is a spring on the front and its a tiny little thing.

I ordered the bucking and nub. Should be here tomorrow. I assume without the nub I cannot really test for air leak?

You can test for air leaks with just a hop rubber in place as you are checking the seal between the nozzle and the rubber.