 He called the new shell design "Extended Range, Full Bore" (ERFB).Starting in 1975, Bull designed a new gun based on the common US 155/39 M109 howitzer, extending it slightly to 45 calibre through modifications that could be applied to existing weapons, calling the resulting weapon the GC-45 howitzer.Bull also purchased the base bleed technology being developed in Sweden, which allowed for further improvements in range.