During the 1960s, the US Army began a programme for a new cannon of 30 mm calibre, the XM140, intended for the abortive Cheyenne attack helicopter. Development work lasted for about 13 years, with well over 1,000,000 rounds being made, in at least ten variations. The programme was known as the 30 mm WECOM (from the Army’s WEapons COMmand).
The definitive WECOM cartridge case, which is not uncommon, is the 30 x 100B. This looks like a shortened 30 x 113B NATO, but did in fact slightly differ in almost every dimension. However, there is another much less common case known to be part of the WECOM programme: a fat, bottlenecked and rimless 30 x 110. This obviously has room for far more propellant than the 30 x 100B therefore presumably developed a higher velocity.
Bob Leiendecker kindly sent me some detailed notes he compiled many years ago on the 30 mm WECOM ammunition. Most of the loadings (actual and planned) he lists use the 30 x 100B case, which was designated the XM193. However, he also lists an XM719 TP and an XM717 HEDP round, both of them being high-velocity loadings using an XM211 case. None of these rounds were actually loaded.
My questions are: was the XM211 case the 30 x 110? If not, what was the XM211 case? And what was the 30 x 110?
The photo below shows dummy versions of the two WECOM rounds, and the one below that shows the XM140 with a 30 x 110 round.