Sr25 Hop

[Pewpewpetie]

Hi, this Sr is doing my head in. Finally got the gb running nicely (cyma platinum sr25) but there seems to be an issue with the hop to nozzle. I replaced the plastic 24mm nozzle( measured with calipers so no guessing) with a shs o ringed type. Problem is, is that any hop unit I try ( stock cyma, lonex, specna rotary ) the hop seems to push the tappet plate back, like they are sitting too far in the front of the gb. Any ideas? Ive tested without any bucking just an empty hop and you can still feel the springy resistance.

[Pewpewpetie]

I believe I know what the issue is, I think the nozzle is too wide for the hop(even the stock NOZZLE) . it's like it's catching where the nozzle tappers, so it can't seal properly and when firing, the nozzle isn't making the full travel into the hop and keeps moving the hop unit causing the magazine to rattle when shooting. Has anyone else encountered this?

[Skara]

38 minutes ago, Pewpewpetie said:

Has anyone else encountered this?

Yes, in my AK when I installed the Combat Union hop. The stock E&L nozzle was too fat and it would not go into battery (read into the hop rubber to create air seal). The CU chamber comes with its own nozzle though so it was just a matter of replacing the stock one.

 

Since it's an aluminium nozzle you could carefully measure the inner diametre of the hop unit and turn it down to spec, you just need a drill/dremel, some really fine sandpaper and calipers.

Your best bet, imo, is to find someone with a bunch of spare nozzles and try them individually on your setup.

Edited June 16, 2021 by Skara

[Pewpewpetie]

18 minutes ago, Skara said:

Yes, in my AK when I installed the Combat Union hop. The stock E&L nozzle was too fat and it would not go into battery (read into the hop rubber to create air seal). The CU chamber comes with its own nozzle though so it was just a matter of replacing the stock one.

 

Since it's an aluminium nozzle you could carefully measure the inner diametre of the hop unit and turn it down to spec, you just need a drill/dremel, some really fine sandpaper and calipers.

Your best bet, imo, is to find someone with a bunch of spare nozzles and try them individually on your setup.

Got another 2 nozzles on order, I've ordered a g3 smooth one, which has no tapper, hopefully that will work. If not I'll have to sand it down. Thanks for replying

[Pewpewpetie]

On 16/06/2021 at 12:32, Skara said:

Yes, in my AK when I installed the Combat Union hop. The stock E&L nozzle was too fat and it would not go into battery (read into the hop rubber to create air seal). The CU chamber comes with its own nozzle though so it was just a matter of replacing the stock one.

 

Since it's an aluminium nozzle you could carefully measure the inner diametre of the hop unit and turn it down to spec, you just need a drill/dremel, some really fine sandpaper and calipers.

Your best bet, imo, is to find someone with a bunch of spare nozzles and try them individually on your setup.

After alot of measuring, milling and sanding I've managed to get a shs nozzle down to size. Needed to be 22.9mm instead of the usually 24-24.2mm sr25 nozzles. Very strange that it requires such a small nozzle. I'll update tomorrow evening once fitted

[Skara]

Does it seal and feed correctly?

[Pewpewpetie]

20 minutes ago, Skara said:

Does it seal and feed correctly?

Yep, the original nozzle was so long that it was not allowing the tappet plate to fully release and made magazine rattle everyshot as the nozzle was smahing against it

[Skara]

This kind of testing is best done with the gearbox closed and the tappet spring installed (real operating conditions).

Glad you sorted it out for not much!

[Pewpewpetie]

7 minutes ago, Skara said:

This kind of testing is best done with the gearbox closed and the tappet spring installed (real operating conditions).

Glad you sorted it out for not much!

Yeah, the first few videos of this post show the resistance caused by the nozzle length. I only opened and tested like that so I could actually see what was happening