At SHOT Shows or other exhibitions, booths of companies like Serbu Firearms are some of the most interesting ones to visit. And the reason is, as a rule, such companies constantly experiment with new ideas and if you are lucky enough, you can meet and discuss their inventions with the actual owners who also oftentimes are the chief designers. This year, I had another chance to meet Mark Serbu and learn about his new creation – a 5.56 rifle dubbed Diabolus.
First and foremost, Serbu firearms are not planning to manufacture this rifle. Instead, they are looking to sell the design to another company. Moreover, there are already companies interested in acquiring the manufacturing rights to produce this rifle.
![[SHOT 2020] Serbu Firearms DIABOLUS Rifle (2)](https://www.thefirearmblog.com/blog/wp-content/uploads/2020/01/SHOT-2020-Serbu-Firearms-DIABOLUS-Rifle-2.jpg)
A left-side FN FAL type non-reciprocating charging handle may be added later.
One of the differences of Diabolus from the AR-18 is the use of standard AR-15 bolts, firing pins and barrel extensions which should significantly decrease the manufacturing costs. This, however, led to modifying the guide rods to fit the cam pin and as a result, Mark ended up with a better design which is now being patented. Here is how he describes this designing challenge and the solutions he found:
What I did differently is to use standard AR-15 bolt heads, firing pins and barrel extensions, which of course means the cam pin is vertical instead of the 9 o’clock position. Because of the small amount of clearance for the cam pin to move between the rods I had to put a small notch in the left one. While I was at it, I lengthened the notch into a flute that runs nearly the whole length of the rod and then repeated it in 120-degree increments. So now both rods have 3 flutes on them which reduces weight and drag, and makes it so the left and right rod are interchangeable.
![[SHOT 2020] Serbu Firearms DIABOLUS Rifle (3)](https://www.thefirearmblog.com/blog/wp-content/uploads/2020/01/SHOT-2020-Serbu-Firearms-DIABOLUS-Rifle-3.jpg)
The pistol grips, trigger mechanisms and magazines are AR-15 compatible.
The lower receiver of this prototype rifle is machined out of 7075-T6 aluminum and to make the upper, they used 6061-T6 aluminum tubing. As Mark notes, both receivers can be also made of stamped sheet metal. The lower receiver has a separate replaceable rear piece where the guide rods are locked into. This solution allows switching between different stock mounting options (AR-15 buffer tube, Picatinny rail, or no stock for pistols) in a matter of changing that rear block. There is also a rear urethane buffer block for the BCG to impact on.
The handguard attachment system is also pretty interesting and unique. The actual handguard is held inbetween rear and front caps. The rear cap is attached to the barrel trunnion and it is connected to the front cap via bicycle spokes! The spokes run underneath the actual handguard. This handguard attachment system still allows having a free-floated barrel and according to Mark, it is extremely strong. The handguard itself can be made of a variety of materials (polymer, aluminum, carbon fiber, etc) and I suppose it can be very slimline and lightweight since all it is is a large spacer between the two caps. The handguard design is being patented too.
To me, this is a pretty interesting blend of new design solutions and existing readily available parts. What do you guys think about the Diabolus? Should it become available, would you give it a shot? And if yes, what price range do you think is justifiable for new firearms like this.