The SCAR, another solution to a non existent problem. Designed to solve the over gassing/over cycling, back pressure, accelerate wear, and cyclic rate issues of the mk18 with suppressor. The believed answer was piston operation to save the day. In the end the answer was the HK 416 or simply better suppressors like the linear pass through designs by OSS suppressors, which results in an almost zero increase in back pressure/over gassing.
From an engineering perspective, the G36 / HK 416 self-adjusting short-stroke piston system is many, many times superiour to the FS2000 and SCAR systems.
The FN design just radiates "Because Belgium" in it's needless complexity, inferiority of which as compared to the HK approach include:
- The need for a tool to fish out the piston instead of that being possible by hand
- The install of the piston from the front of the firearm instead of the back (can be argued as also a safety problem) means that piston can get stuck in the firearm
- The two-position gas regulator switch that means you need to touch a possibly scalding hot part of the firearm if you need to adjust it in the midst of shooting (eg, your suppressor fell off/was shot off)
- The screw-in gas regulator screws on the FN gas block can be lost or can migrate into the piston chamber and, well, it's like a family of raccoons got in there with everything destroyed
- The FN gas block is at a 45 degree angle to the firearm, which is weird (not really a bad thing, but a blatant reflection of "Because Belgium" thinking).
- The FN trunion is a screw on affair held in place by a counter-rotating castle-nut which has it's problems when trying to get things to work together, (just like Molenbeek). To head-space a barrel the trunion needs to be screwed on first so that the bolt will fit and rotate, but not be loose. Then the castle nut is screwed on and hopefully it will torque against the trunion without moving the trunion from the set position. Then the chamber can be cut (good luck returning the trunion back to the exact location it was when you measured everything out! Or keep the trunion on and hope your tools can clear). Oh, yeah, and that gas port and the two pin slots on the other end of the barrel that need to be cut too? Good luck getting them to alight exactly at 45 degrees with the trunion. If you mess the alignment up by a degree or so you will either get an out-of-spec chamber (because the trunion will need to be rotated) or the piston will only strike the rod partially, eventually bending it from the asymmetrical forces (good luck finding a replacement rod).
Grafting the self-adjusting G36 / HK 416 gas system onto the FS2000 / SCAR might be possible with a custom gas-block because the distance between the centre of the barrel and the piston is greater on the FS2000 / SCAR then on the G36 and the barrel dimension is smaller on the FS2000 / SCAR than the G36 / HK 416 (14 mm vs 15 mm). A custom barrel with a 15mm diameter will require the barrel support to be reamed out to 15 mm, and doesn't solve the issue of the centre distance differences. A replacement gas block design is seemingly the only solution, but then the issue is that the FS2000 has the recoil-rod attached to the bolt carrier group while the G36 / HK 416 has a very short impulse where the piston travels about 10, 15 mm and gets pushed back into the cylinder by the recoil rod that travels independent of the bolt carrier, while in the FS2000, the rod travels the length that the bolt-carrier travels (10, 15 cm). So the question remains on how to keep a G36 / HK416 piston in the gas block on the FS2000 system, which explains why the Belgians when with the piston being "trappable" in the gas block: else, with the first shot, the piston might fly into the receiver. So the gas block would require a trap of sorts, probably a screw-on shroud to trap the piston.
