The updated truck mounted 122mm MLRS (Multiple Launch Rocket System) Russia introduced in 2012 has received its first combat experience in eastern Ukraine (Donbas). Called Grad-K, the truck mounted system apparently entered Ukraine at the end of 2015 and was seen in action several months later. The loaded forty tube launcher, the three man crew and 6x6 truck weigh about 15 tons. All 40 rockets can be fired in two seconds using a computerized fire control system that uses satellite navigation. The launcher can be reloaded in seven minutes and it takes less than three minutes for the truck to stop and be ready to launch on a target.
Grad-K can use a wide variety of 122mm rockets built to the basic BM-21 specification. The older BM-21s weigh 68.2 kg (150 pounds), are 2.9 meters (9 feet) long, and have a 20.5 kg (45 pound) warhead. The BM-21 rockets have a maximum range of 20 kilometers. Again, because they are unguided, they are only effective if fired in salvos or at large targets (like cities, large military bases, or large groups of troops or vehicles on the battlefield). There are now variants that have smaller warheads and larger rocket motors, giving them a range of about 40 kilometers.
BM-21 was introduced in 1962 and replaced the World War II era BM-13 132mm rocket. That weapon entered service in 1939 and each rocket weighed 23 kg (50 pounds), was 600mm (24 inches) long, had a 4.9 kg (15 pound) warhead and a max range of 11.8 kilometers. The BM-21 was a big improvement.
Around the same time Grad-K entered service China introduced the new PR50, a much improved Russian BM-21 that began in 1989 as the Type 81 (a strait copy of the BM-21). The PR50 system uses a 122mm rocket that weighs 74 kg (163 pounds), is 2.9 meters (9 feet) long, and has a 21.5 kg (47.3 pound) warhead. Minimum range is 20 kilometers, while max range is 40 kilometers in a version that uses a lighter warhead. The PR50 is actually a complete system, including a truck mounted launcher that holds four 20 rocket launcher boxes. The truck has an automated aiming and reloading system. The PR50 rocket is interchangeable with the older BM-21 type rockets. The main difference between the PR50 and Grad-K is the Chinese system uses a longer 6x6 truck which carries 40 rockets ready to launch and two 20 rocket pods as reloads. The truck carries a crane that makes it easy to reload.
As can be seen with the Chinese PR50 the original BM-21 design is hard to completely replace but improvements can be made.