Iran is unhappy with the results of the recent Gaza war. They are particularly annoyed at the poor performance of the Palestinians they trained, in the latest tactics and weapons handling techniques. These guys, about a hundred of them, were quickly wiped out by a smaller number of Israeli troops.
Also disappointing was the use of longer range rockets by Hamas. While about 600 rockets were fired into Israel during the 22 day campaign, only a few dozen were of the long range BM-21 type, and these did little damage.
The 122mm BM-21s weigh 150 pounds and are nine feet long. These have 45 pound warheads, but not much better accuracy than the 107mm model. However, these larger 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, or large military bases or industrial complexes.) There are longer range (up to about 40 kilometers) versions of these rockets. These are made by a number of countries, and gain their additional range by using smaller warheads.
Most locally made Hamas rockets (Kassams), are based on the older Russian B-12 rocket. This is a factory made, 107mm, 42 pound, 33 inch long, Russian designed rocket that is very popular with terrorists. This rocket has a range of about six kilometers and three pounds of explosives in its warhead. Normally fired, from a launcher, in salvoes of dozens at a time, when used individually, it is more accurate the closer it is to the target. This 107mm design has been copied by many nations, and is very popular with guerillas and terrorists because of its small size and portability. Hamas has little need for the B-12, because their locally made Kassam rockets match it in range and lack of accuracy. But some B-12s are smuggled in anyway.
Iran would like to smuggle longer range rockets into Gaza, like their Fajr-5. This 10 meter (31 feet) long, 333mm (13 inches) diameter, .9 ton rocket has a range of 75 kilometers. It could reach Tel Aviv, and most of central Israel. But the Fajr-5 is as big as a telephone poll, and is based on a similar Chinese rocket that Iran bought in the 1990s. Fajr-5s could be moved through the smuggling tunnels to Gaza only if broken down into 8-10 sections, and then reassembled on the other end. Getting the pieces into Egypt would not be easy, and trying to smuggle them in by sea is very risky. The Fajr-5 carries a 200 pound warhead, with about a hundred pounds of explosives. Makes a big bang, and is only effective if aimed at a large urban area. That means that the most likely victims will be civilians. Iran is betting that Israel will not retaliate when Israeli forensics experts examine the pieces of the missile after landing, and identifying it as of Iranian manufacture. Israel did not strike back at Iran when smaller Fajr rockets were fired at Israeli cities in 2006. But Israel would certainly go into Gaza if a Fajr ever landed in Tel Aviv.
Iran feels humiliated now, by the country it says, loudly and frequently, should be destroyed. So there may be an effort to get Fajr-5s into Gaza. But getting Hamas to fire them is another matter. Hamas is under a lot of pressure from European and Arab supporters, to give up its genocidal plans for Israel and to concentrate on improving the lives of Gazans (many of whom blame Hamas for the recent war). Even Hamas hardliners have to confront the fact that they put in a pitiful performance against Israeli troops recently. Firing a few Fajr-5s into Israel, and then getting blasted by a thousand Israeli smart bombs, missiles and artillery shells, gives one pause. But Iran is supplying Hamas with much of the cash that keeps the organization alive. So Hamas will go along with plans to replace the 2,000 rockets it lost in the recent war (including 1,400 destroyed by Israeli bombs, shells and troops.)