Regarding the low FPS and possible nozzle issues, try the old o-ring in the t-piece mating surface trick and see if that helps to seal properly. 
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Iāll see what 2morrow brings.
If itās beyond me, Iāll take it to xforceā¦
Itās a old rarity, worth preservingā¦
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HQ MP5K, and yes 2017-2018 is about the time they were aroundā¦ in small numbers, as a shell kit only.
To give an idea of rarityā¦ excluding me, BME and DocBob, I only know of one other person with one!
And they are a prick to assemble for sure.
I designed and printed a mag terminal plate that made it work with ldt mp5 mags, and it took several times assembling and disassembling it to get it rightā¦ took far longer than. Iād like to admit, and ldt mags are a bit of a tight fit, but I didnāt want to modify the receiver to suit, due to its rarity wanted to keep it original!
Does sound like a nozzle/tpiece issue, been too long since I worked on mine to remember any details of assembly.
I do use a small zip tie around the tpiece section of the gearbox on a gen8, as it keeps the front together nicely and prevents the barrel being misaligned to the nozzle. Being such a tight receiver it could be a factor?
Could also be the nozzle is a bit tight and not moving freely enough?
Best of luck with it today.
Fun fact, they fit ldt buttstocks perfectly if you want to go that route 
Interesting morning.
Pulled it all apart again.
The brand new Nozzleā¦had done thisā¦
Thats two for twoā¦whats going on?
The tpiece is semi transparentā¦
I cleaned up both nozzles, and reattached with super glue.
The old one was fine, the newer one didnt quite seat all the way down, and sits just a little proud.
I was going to reuse the old nozzle.
However, it was as if the rubber had expanded, and was now VERY tight in the tpiece.
As in, you had to push it in, and easy movement was hampered.
So, i went with the new, slightly proud t piece.
It moved, without any binding, in the tpiece.
Test run time.
It cycled fine, on the naked frame, with motor attached.
Holding a full mag tight up into it naked, the mag operated flawlessly, it fed and fired flawlesslyā¦
Consistent 260 fps. Still good for a short barrel.
Not quite the 280 i was hoping for, but maybe a slightly dodgy nozzle may be playing a part.
I donāt know how long a superglued nozzle will hold forā¦
What glue do they use, to attach them at the factory? Something stronger?
Accuracy is awesome as wellā¦the whole inner barrel is tightly gripped by the outer barrel. No barrel movement whatsoever is possible.
As soon as i began to assembleā¦the mag wouldnt get power to it.
When it was apart, i gave all the terminals another good clean.
So, its gotta be poor physical contact.
I gently bent the receiver springs down a little.
I dont wanna go too hard on themā¦ they are part of a funny little custom assembly. Break emā¦good luck finding sparesā¦@docbob??
Looks like the solution is to build up the terminals with some solderā¦
Ugghhā¦ solderingā¦not my strong suite (yet).
Gotta be careful of melting the mag plastic.
Can you hold it close, and drip solder onto the contacts, to build it up.?
I dont wanna ruin the ( rare as) magsā¦
Hmmmā¦
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@docbob, i dont know how many mags you have, or want to part with.
For any you do want to get rid of, I would happily buy half ( the other half available for @roksolid).
No rushā¦whenever you can get around to it.
Maybe other mags might have higher/ better terminalsā¦
Varying Chineseium standardsā¦!!
I use gorilla super glue impact tough for nozzles and cylinder head pads. Itās shock resistant, cures quick and has a little working time to get it positioned wellā¦ still have to be quick but not like regular CA glue that is almost instant.
Otherwise I donāt mind the gorilla glue super glue gel. It probably has a bit more working time but does take a little longer to cure.
Both have worked fine and never came offā¦ just be sure to scuff up and clean both surfaces with isopropyl alcohol, as oil and lubes will absolutely stop it working.
Coolā¦ iāll do that next time.
Im kinda expecting this one to fail.
I might even buy another nozzle, in anticipation.
Iāll have a play at dribble soldering onto scrap here, and see if i get confident enough to go near near the magsā¦
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I second Gorilla glue, what I use.
Soldering, if you got some surpurflous bin job old electrical appliances around practice on the cords or any electronics in them desolder/resolder any chips on boards or something for good practice.
Ok, i felt brave enough to have a crack.
Clean, flux, and ā¦what the fluxā¦!!
Got some blobs onto the right spot, not pretty, but got it workingā¦
It needed quite a bit of building upā¦mag now sits very tight in magwell.
I Wont be leaving it in , sitting for long periodsā¦
Mags seems to be a little tighter when its all reassembled, as to not having the lower.
Better FPS results.
Why cant the @#$%%# Jinming MP5-Kās do thisā¦??
Gen 8 ported voodooā¦??
EDIT: i just realised ā¦ i was building the contacts up, with the magwell tabs OUTā¦this had the magwell sitting LOWER than its proper position.
Hence, more buildup reqd to make contactā¦and firmer to get a mag in, now its back together.
But whatevs, it all still worksā¦
The trick of reassemblyā¦
Box and barrel slides neatly into the upper.
If you have removed the magwell and reinstalled itā¦make sure the lateral upper tabs go INSIDE the upper reciever.
They look innocuous, easy to missā¦but if you do you it will be impossible to reassemble, and youāll need to pull it all down again.
Ask me how i knowā¦!! 
Importantly, put a mag in, make sure it lines up with the tpiece / fires/ feedsā¦then LEAVE IT IN.
This ensures everything for the mag remains aligned as you grunt and heave reassembling.
Lower goes on fairly straightforwardly.
With magwell lateral tabs IN, you can get the front pin in easily.
This is the workoutā¦the final rear pin.
El muchacho el bastardo satanoā¦!!
You end up pushing, squeezing and twisting the shell, to get the pin in one endā¦guiding it through with a screw driver to get it close to aligning and lining upā¦ then pushing it down with the other hand.
I cheated a little, and filed out some of the outgoing hole, to make it a bit wider. It shouldnt have top be that tough.
When its in , there is a lot of pressure on the final pin, but it keeps the blaster Rock Solid immovableā¦( couldnāt resist!!)
Final outcomeā¦
Back into the 270-280 fps rangeā¦ on i Hobby frosted whites.
JM mp5kāsā¦cmon.!! you can do itā¦!!
Thatās the best iāve seen, for such a short barrelā¦!!
It feeds and fires flawlessly now, as it first did.
Maybe a touch too much solderā¦but mags are now super tight.
Note to selfā¦Possible failures in the futureā¦
Nozzle head coming off again.
Solder eventually vibrating off.??
Iām a bit perplexed how the mag fed originally, without that extra solder.
I stored it with the mags out, so the springs shouldnāt be compressed.
All done for now.
@DocBob āTowel Ranking systemā TM
Green for newbies, yellow for intermediate, red for mastersā¦!!
Top work mate and great results for such a small barrelled Gen8 power system. 
Love the Towel idea, certainly gave me a good chuckle!
Gotta admit that theyāre the best surface to work on though, where random loose parts and flying springs get caught and held on the spot pretty well, always have some cloth to wipe hands/parts on, and simply throw into the wash for the next project.
I think our original agreement was 2 mags each for you and @RokSolid .
1 X Single and 1 X Double Mag each.
That will leave me with 2 X Mags for mine.
The original Mag it came with plus one spare. 
Just realised that thereās only one Single Mag available, but thereās 2 X Dual Mags plus 2 X extra Dual mag adaptors.
So can each have a Dual Mag and adaptor each, but will have to fight with @RokSolid as to who gets the stand-alone single Mag! 
At least with the Dual Mags, they can be split and the motor powered side used as single Mags if required anyways.
The oneās I have available are on the top of the box, whereas the original Mag and Dual Mag on the bottom are what Iāll be keeping for my HQI MP5.
āWhite towelā TM is for when you quit, and take it to a techā¦!!
Not todayā¦!!
Thanks for the very kind and generous offer of making these rare mags available.
Iāll defer to @roksolid for the singleā¦his choice first, if he wants it.
If he doesnāt want it, iāll take it.!
Once thats decided, iāll shoot you a pm for payment / postage etc.
Thanks againā¦!!
No worries mate, better off parts go to people who appreciate them and are actually able to use them, as the bits Iām holding onto are for display purposes only. 
are my eyes deceiving me, or are some of those mags (semi) transparent.??
And yeahā¦towels are good.
Saves scratching the kitchen bench, doesnāt mark the outer shells, and bits caught as you saidā¦
Yes, they are all semi transparent dark tinted plastic, the same as the original tinted plastic parts like your t-piece.
I only have one full black mag that I got with the Blaster, but all spare mags are the tinted see throughā¦ so unsure if factory HQI accessories or aftermarket, but makes sense that they are original HQI accessories if they are made from the same type of plastics as other parts in the blasterā¦ especially considering that they were the only MP5 on the market at the time, I donāt know if any other companies would have been manufacturing aftermarket Magazines to fit these rare low volume Blasters? 
Doesnāt matterā¦ Iāll grab emā¦!!
Leave em original for novelty value.
And, if my original black one diesā¦just transplant the partsā¦