The Zelos is a bullpup PCP that stuffs 26 inches of barrel into a compact 36 inch package. The natural result of such a long barrel length is power and accuracy with the added convenience of a very easy handling bullpup platform.The Zelos in .25 caliber utilizes a 18 round auto-indexing rotary magazine and features an on-board tank that fills to a maximum pressure of 3625 PSI. This 250cc tank is free-floated from the barrel and fitted with an 8-slot Picatinny accessory rail. Zero in your favorite optic on the 21-slot top Picatinny rail and start sending pellets downrange with precision. In fact you will be able to easily tune the Zelos to your best perfoming ammo via the reciever-housed adjustable regulator.Feel free to shoot the Zelos the way it comes out of the box or attach an aftermarket muzzle device to the 1/2" X 20 threads found underneath the barrel nut. 26 Inch Barrel 250cc Tank 3625 Max Fill Pressure .25 Caliber 18-Shot Auto-Indexing Magazine Tank Mounted Picatinny Rail Top Picatinny Scope Rail 1/2"X20 Muzzle Threads 6.74 Lbs 14.75 Inch Length of Pull Adjustable Regulator 6.98mmX4.33mmX1.5mm Tank-to-Reciever O-Ring (ODxIDxThick)