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WE/Iron Airsoft/Prime Remington R5 GBBR Custom Build


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WE Remington R5 Custom Build

I purchased this Iron Airsoft R5 for the WA system over two years ago, and just about a month ago I found it again tucked away in my storage unit and got to work trying my best to convert it to the WE system.

Full parts list here:

* Iron Airsoft R5 upper receiver (Cerekoted in Patriot Brown (needs to be redone sometime soon))
*Seekins Precision DNA charging handle
*Angry Gun gen 2 steel bolt carrier
*(Not currently installed) Poseidon ZERO 1 WE nozzle
*Angry Gun WE M4 hop-up
*Falcon Double point VS-Z 80 degree hop-up bucking
*Falcon 6.03 330mm CNC Copper alloy inner barrel
*Custom outer barrel/hop-up collar pieces.
*WE MSK flash hider
*Daniel Defense rear fixed sight (didn’t come with the screw and all the standard length screws were too short)
*Tippman flip up front sight (soon to be replaced with the Daniel Defense front fixed sight)

*Prime WE Magpul Lower (Cerekoted in Patriot Brown (needs to be redone sometime soon))
*Stock WE trigger assembly (Wii Tech may be making WE parts, I’ll probably move to them if they do)
*Angry Gun anti rotation pins
*V7 ambi short 57-90 degree selector (currently at the 90 degree position)(Locked to semi only)
*V7 magazine catch
*V7 body pins
*Daniel Defense buffer tube
*Unknown brand H buffer
*Unknown brand buffer spring, looking for a Viper Tech spring
*Stock WE castle nut and end plate (being replaced with V7 castle nut and end plate)
*BCM MOD 2 pistol grip
*BCM MOD 0 stock
*ERGO Suregrip (not currently attached)
*MFT minimalist stock
*Airsoft Platz Stiffy Knob


The two most important parts of this build are the Iron Airsoft R5 upper, and the Prime Magpul WE lower. The Prime lower is number #10 out of the #100 officially licensed lowers Prime made, which makes it all the more special. The lower, being designed for the WE system didn’t take any special work to get working, though I did need to very lightly mill off a small amount right above the front body pin to allow the uppers to close together. 

The first set for the upper was to extend the auto sear cut as far as possible to allow it to make with the WE lower. The WE trigger box, specifically the portion with the valve knocker extends upwards farther than on most systems and needs the cut so the upper and lower can mate.


On a standard WA to WE barrel adapter, there are tabs on the 12 o’clock and 6 o’clock positions which extend into and keep the WA barrel in place, and then further up tabs on the 3 o’clock and 9 o’clock positions which extend into the WE hop-up, and by extension the WE upper receiver. Here's the GunsModify barrel adapter:
And my adapter for reference:

The IA R5 outer barrel is different from standard WA based barrels. For the R5 barrel, the barrel extension also acts as a barrel collar which lines up with the secondary collar which locks into the receiver. The first part I made was similar to the WA to WE barrel adapter, though I extended the piece 2.5mm, and excluded the tabs for the WA outer barrel. This piece helps keep the WE hopup centered in the other piece, along with the tabs in the WE hop-up. The tabs on the WE hop-up also needed to be filed down to properly fit into the receiver.


The next piece holds the WE hop-up in place along with the modified barrel extension, and then threads into the R5 outer barrel. After threading all of the pieces on everything sits extremely secure with no movement. Both this, and the barrel adapter part were printed in Shapeways Fine Detail Plastic for the highest quality prints. I am in the process of getting both parts machined out of aluminum, though I won’t have those parts available for a while.




In order for the real selector to work properly with he WE parts, the disconnector needed to be filed down slightly. Otherwise the gun fired auto while set to semi-auto.

The last parts which required some custom work were part of the bolt catch assembly. For whatever reason Prime designed their lower in a way which does not allow the stock WE bolt catch pins to fit, needing a larger. I 3D printed the bolt catch pins to get the fitment right, and will eventually get the larger WE pin turned down to fit. The stock, heat treated steel WE bolt catch also needed to be filed down to fit.



The R5 outer barrel secures into the upper received using four M5x10 screws and a locking plate. Iron Airsoft’s method for locking these screws involves you sticking an allen wrench in the small open slot, rotating the screw maybe a 6th of the way, over and over and over. This took ridiculously too long, so I purchased a 19” T-handle allen wrench from McMaster-Carr which cuts the barrel attachment/removal time down to a minute or two.



Lastly, a few of my MSK magazines have the Remington “R” engraved into the lowest portion of the magazine shell on both the left and right sides. These were originally sold by Sanko Shop back when the WE MSK was first released, though they dried up years ago. I just purchased 6 new black MSK magazines and will be having them engraved within a week or two.


While not necessary for the build itself, both of my grips can comfortably hold the Airsoft Platz Stiffy knob, which helps tremendously for hop-up adjustment.


This build still has a lot of tweaking and time to be put into it, though the hardest parts are out of the way. Lemme know what you think!

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Got a few more parts in!

Daniel Defense front and rear sight are installed, replaced the forward assist with a black piece rather than the grey (still need to replace the dust cover)
The biggest additions are the pair of 3d printed angled grips. Considering the Cadex rail system being used I couldn't use something like Mlok and needed to design my own grips. I'm pretty proud of how they turned out, though they are pretty bulky compared to the Magpul grip for example. I might make them a little bit more ergonomic later down the line, just depends where I want to go with it. Stuck with the flat back side to leave the option for putting maybe a standard foregrip behind it.


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14 hours ago, Katotaka said:

Very cool build!

Didn't know that MPL receiver is THAT limited....... just checked mine and it's indeed below #100

Things could have changed, though I haven't seen any numbers over 100. This Popular Airsoft article on them mentions it as well. https://www.popularairsoft.com/news/prime-magpul-upper-and-lower-receivers-we-m4-gbb-coming-september What number do you have?

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