It’s hard to find a more contentious topic in the AR world than “piston vs. DI” – that’s why it’s nice to have some hard data to work with.
Vltor conducted testing of 10.5″ and 14.5″ HK416s, specifically, their rates of fire, both suppressed and unsuppressed – incredibly, the 416’s rate of fire with the stock buffer was as high as 1106 rounds per minute suppressed (10.5″), and 941 rounds per minute unsuppressed (14.5″). That’s incredibly fast, and can cause a host of issues – among other things, many magazines just won’t be able to keep up with such a high rate of fire. It’s also harder to control a weapon that cycles at that speed, either on full auto or semi auto.
For comparison purposes, a Colt M4 is designed to shoot 800 rounds per minute unsuppressed.
With the Vltor A5 stock system and its extra heavy buffers, however (5.3oz stock, 6.1oz A5H3 and 6.9oz A5H4), rates of fire decreased to more manageable levels – 788 unsuppressed, and 914 suppressed (with the A5H4). That’s a decrease of 187RPM for the suppressed setup. That’s an incredible drop, and will increase the service life of certain components while making the weapon easier to shoot. Interestingly enough, the HK416’s rate of fire (with the standard, non-A5 buffer system) is almost identical to some LWRC data that was recently posted on M4Carbine.net. Some other piston ARs have similarly fast cycling times.
If you want to know a little more about the A5, check out the video I made a few days ago –