Magna Ballista is a gas operated firearm with a piston located above the barrel. The action lockup is accomplished via rollers. Note that the rollers here are merely locking lugs (like in the MG42 machine gun), they are not a part of a blowback delay mechanism like in HK G3 or MP5. In other words, Magna Ballista is a roller locked, not roller delayed blowback firearm.
The charging handle of the rifle is reversible. The gun has a cross-bolt safety. The cheek rest area of the upper receiver is reinforced to protect the shooter in case of a catastrophic failure. Additionally, the rifle is designed to vent the gasses down into the magazine in case of a kaboom.
Magna lists the following caliber options for the Ballista rifle: 9x21mm, 5.56x45mm, 7.62x35mm (.300 Blackout), 7.62x51mm, 7.62x54mmR .338 Lapua Magnum, .510 Whisper and 12.7x55mm. The latter is the cartridge used in Russian VKS Vykhlop and ShAK-12 suppressed bullpup rifles. The version in 7.62x54R is apparently fed from SVD magazines. I am not sure how efficient it will be to chamber a gun like this in a pistol caliber … I assume the 9x21mm is included in the list to show the caliber conversion capabilities of this weapon system.