If you do enough hunting for AR-15 parts you will eventually hear about OTB rifles. HK416 and other clandestine aimed weapons often have these features. What are the you ask?

They are nothing more than some small, strategically placed holes which allow water to quickly drain from the gun. Many high-end assault rifles and even some semi-automatics will have OTB magazines, receivers, and buffer tubes.

Rifles setup with OTB parts ensure they will be able to fire immediately after being submerged in water.

As you can see in video below, the OTB buffer tube in the HK allows the water to drain and bolt to freely move as intended.



Interested in making your own OTB magazines? Here is a hint... Try using a 1/16th drill bit in the floor plate.