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HK21 Build


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I've been posting the occasional update on Reddit, but thought I'd share here too.

I'm using what I *think* is parts from a G&G FS51 to create something like the image below:


So far I've taken the stock and moved the crook backwards to look closer to the correct stock, here's the original compared to what I've made:



Next to the stock is the quick change barrel handle that I've made using ABS sheet plastic, cut on the bandsaw and layered using a coldweld solvent:


Here's what I've made so far, using aluminium tube for the handguard, sawed out and shaped with files. The cocking tube and outer barrel have been cut and extended using 20mm steel tube, and are epoxied and pinned in place. The box mag has had the internals stripped out and replaced with a 16mm push button:


Next up is the new magwell/feedtray which will be aluminium sheet, and adding the upper rails to the reciever and cocking tube, these parts are due in next week.

The box mag will be mounted onto a cut down G3 magazine, so that it can feed reliably and be easily be removed for the safezone.

I have an FS51 lower and fire selector on the way, but potentially up to a 25 day wait due to the pandemic.

More to follow!

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Small progress update, have built the mock forward assist, which seems to be a TSC Machine specific feature:


Have also cut and bent the new magwell/feed tray, but this isn't attached yet. There's a half built feed inlet on the other side but I'm waiting for epoxy to dry on the receiver reinforcements for now. Reinforcement will also be added to the right side of the receiver, covering the stock channels as per the real version.

Rail sections should be arriving early next week, so will have upper and front rails, plus bipod rail installed soon.

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The plan is to have the box mag feed a regular mag like a giant hi-cap. The regular mag will be cut right down and mounted to the box mag, and also modified to slot straight upwards into the mag well rather than rock back.

A pin will then go through the magwell and mag to hold the box mag in place rather than using the mag catch (as I don't have one/it wouldn't look right).

The feed tube ala 249 will still be used, but it won't be seen. The feeding side of the mag will have a fake 5.56mm belt added into the feed port.

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Good point, my original intention was for this to be based on a CA33 body, which is 5.56, but was sent the wrong receiver.

Already had the box mag and definitely forgot until now that the two are different calibres. Worst case scenario and it looks off, I'll fab up a new box to go around the 249 box.

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Saw your posts on Reddit; this is an ambitious project and I'm interested to see where it goes.

I'm not sure if this is what you meant you were going with, but with the 6mm ID spring tubing used for machine guns you should be able to splice the box mag into the regular magazine's feed track internally, allowing it to feed like a normal AEG.

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Slight visual update:

- Rails added to the receiver and front end

- Cocking tube, barrel, and front assembly permanently bonded to the receiver

- Hard to reach bits (back of barrel, inside of handguard) painted black

- Barrel change handle mocked in place

- Swing to side butt-plate halfway done

- Stock channel reinforcements added


Next steps are fixing the handguard permanently in place, fixing the barrel change handle in place, and finishing the butt-plate.

Still waiting on the lower receiver, selector, pins etc.

Strongly considering taking the easy way out and making this the drum fed version. I've made a cover plate and feed port but I'm not 100% happy with the result, so maybe a drum would yield a more professional finish.


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Man, that's really awesome. Great fabrication work on all of it- very different skills involved in laminating ABS and cutting tubing, but you've really made it look the part. I have no particular input on drum vs belt; the belt-fed variant would certainly be more unique, but having the result not live up to expectations can be really frustrating. Would it be practical to get a real feed tray from another platform?

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Thanks, it's certainly a different skill set to my day job!

For me the cost of gambling on modding a feed tray from another platform wouldn't really be worth it as this is a super low budget build so far, ~£60.

I think the biggest let down on realism is that the feed port doesn't go anywhere as the hop up and gearbox are in the way, whereas on the real version you can see straight through.

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  • 1 month later...
  • 1 month later...

Long overdue update, parts arrived and everything is painted. The only thing left now is to build the butt plate.

I can't install the trigger or selector switch as I have no gearbox for it currently. Chances are it'll be put up for sale once finished, so probably won't bother getting a gearbox for it.


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