In June 2024, I created an MSBS Grot conversion kit for the ACR A&K platform.
https://benen3d.myshopify.com/blogs/acr-a-k/conversion-acr-en-msbs-grot
But this time, I’m starting from a blank sheet since no basic platform will be used.
The specifications are as follows:
1. MSBS Grot C10.5 A2 replica
2. Replica AEG, so it is necessary to define the internal
You can see that it looks very similar to an ACR, which is a platform based on the V2 gearbox with a long nozzle.
3. As few proprietary parts as possible on the internal...
What is remembered, after studying, is:
- A Gearbox V2 with long nozzle (ACR nozzle)
- A Hop Hup M4 unit, Prowin/Rotary type
- An AR pattern magwell for compatibility with any M4/AR15 Airsoft mags.
- An external metal barrel threaded in 14mm CCW
- A retractable stock, with battery compartment
- All in a 3D printed body kit
And it’s time to tackle the main course: MODELING...
(I would not intentionally go into detail about obtaining the quotes or developing certain parts of the platform).
And the Lower, it’s clearly not a small bbq...
The geometry is more complex than an AR15, but it’s not something that will stop me.
After a few hours of modeling...
The result is very close to the real one, if not identical, because it was necessary to modify 2 or 3 places since the body must accommodate a Gearbox V2.
Here is the lower with the addition of the V2 gearbox, and the Hop Hup unit.
The Lower is a bit of what will define everything else. And also the centerpiece of the project. I took quite a long time to get this result, mainly using photos from several angles as supports.
Once done, I can draw the remaining. (The grip is for information only, it’s an illustration template.)
The ACR’s stock has not been reused; it is thinner, since it is adapted to the ACR.
The stick had to be completely redrawn to match the Grot.
A few hours of modeling later ...
More hours of modeling later...
A small rendering of the replica in its complete configuration:
And here is the prototype that validates the design...
Installation of an internal in the prototype, and validation by the future owner.
The replica is sick with the stock being replied.
Another small detail I added: the sights.
The modification took place on the logos, so I embossed the logo instead of extruding it onto the magwell.
I’m also changing the markings to "5.95mm" and "PL 2025" on the upper.
Once the validation is completed, we move from prototyping to final production.
Here is a comparison between 2 lowers of final quality and a lower prototype:
Meanwhile, Upper's assembly.
Functional cocking lever, 14mm CCW metal barrel
Ejection window, ejection guide, gazblock, and gazblock adjustment knob in SLS printing
Small aside about the Main Guard in 16":
And here is the complete kit:
A project that started at the end of 2024 and ends in late 2025/early 2026
Hundreds of hours of modeling
Dozens of hours of prototyping, and reflection
Finally, a good hundred hours of production
A few dozen prototype parts
A body that is made up of about thirty non-internal pieces
And here we are with the first replica of the Polish assault rifle, the MSBS Grot C.
As usual, it’s a world first.
Obviously, at the time this blog is closed, version 762N is in progress.
https://benen3d.myshopify.com/blogs/msbs-grot/msbs-762n
Next one !