MK V2 into the HLF ARP99

I got a chance this evening to do a quick strip of the HLF variant of the ARP9. At first I was certain that they XYL and HLF used the same receiver but that’s not the case and I’ll save that for another thread. You’re here for the gearbox right. So this looks to be a badgeless warinterest box. The 2.5 or version 3 perhaps. It looks the same as the box from an LDT HK416.

Which means…

The MK V2 box is a fit.

If you are in a pinch you can transfer the internals of the box into the MK V2 shell. Expect a few tight squeezes since the plastic internals aren’t exactly made to a tight tolerance.

I’d use the loom and cylinder head again.

I’d bin the trigger block piston head and piston, nozzle, selector plate.

The grip lines up perfect!

T Piece sits almost flush against the box. The barrel retainer spring needs to be stretched IMO to push it up against the box a fraction for the ultimate nozzle seal.


So the thing… the one big thing that I questioned the whole time with this gearbox was if it suffered from the same problem as the LDT 416. Meaning the box is not a true V2 so they changed the receiver pin location a fraction to suit the box. Rather than simply using a V2 box. Sadly it suffers from the same flaw :frowning:

The rear pin does not line up perfectly and a 1mm modification to the receiver is required for the V2 box to be secured to the receiver…

I had with my Hawkex tactical 416d the rear pin did not line up.I could still get mag release and the trigger pin in but not rear cross pin.This put gbox in at a slight upward rear angle
Stock (12)
I had to remove material from the rear of the receiver to get the gearbox back a little bit and then it all lined up fine with a retroarms gbox.
Modified (6)
Mine was also noticeable as the gbox sat crooked. Can’t see that in your pic

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Will have to do a side by side with Retroarms to MKV2.
These are WarinterestV2 series2 to Retroarms V2 comparison with a pin through the back bolt hole.

20190816_115919 20190816_115949 20190816_120015 20190816_120053

only thing is i did not take a pic of tail of the boxes to show the retro being longer. Will do a comparison of aps v2, MKv2, slr, MK92, J9/10 boxes on the weekend. Why i did these pics was the difference where the grip goes on. Think it shows importance on checking your grip to receiver interference


Look forward to some more pics thanks. :

In all their wisdom Warinterest have decided to move the 6mm pin hole by approx. 1mm in 45˚ direction. This is classic JM move where everything is slightly off by 1mm or less. Its hard to say whether this was done on purpose to force purchase of only their internals or is just Chinese measuring standard.
In any case from Warinterest v3.0 you can expect to do same mod to the receiver with any V2 gearbox other than the Warinterest one :frowning:
v2.0, 2.5 is standard v2 fit


Thanks for the input.
All the gear boxes i got here that i was going to line up have different pin hole diameters as well.
Will still do the length comparison as it may help others not using Warinterest V2 series3 box.
Also edited above pictures as the Warinterest gearbox is a series2.

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MKTH V2 is the same length as Warinterest v2/2.5 so can use Warinterest T Piece without mods.
With Warinterest v3.0 length is the same but god only knows why they would move the 6mm pin hole so that it effectively doesn’t align with any other v2 receiver or Gearbox

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Mines cursed, 1st attempt with 16:1 and purple chai hai 39k motor gb dropped a bushing and bent spur gear axle after 2 mags,
2nd attempt new bushes new 16:1 same motor, after another 2 mags the ladder gear exited piston bent round the sector and bent spur axle again.
3rd attempt gave up thinking I have no place building anything other than high fps builds, sent to a tech, new piston new 16:1 new bushes and replaced perun with leviathan and ditch 39k motor for m150, got blaster back after 4 weeks doesn’t feed checked for errors on leviathan unplugged battery went to sleep woke up and mosfet dead​:exploding_head::exploding_head:

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