dud rates vary according to year of manufacture, country of manufacture, factory source, and of course bomb types. weather conditions can affect detonatio rates as can humidity levels
i know some details about cluster bombs. IDF reports estimate dud rates for their anti-personnel cluster ordinance to be 14% in the typical conditions of their area of operations
Even though cluster bombs are designed to explode prior to or on impact, there are always some individual submunitions that do not explode on impact. The US-made MLRS with M26 warhead and M77 submunitions are supposed to have a 5% dud rate but studies have shown that some have a much higher rate. The rate in acceptance tests prior to the Gulf War for this type ranged from 2% to a high of 23% for rockets cooled to −25 °F (−32 °C) before testing. The M483A1 DPICM artillery-delivered cluster bombs have a reported dud rate of 14%.