This is really far out but the US has started to work on the XM907 ERCA 52 caliber Gun-Howitzer with an eye to applying it towards M777 and M109 modernization programs.
http://defense-update.com/20160329_m777er.html
ERCA involves everything from development of an autoloader for the SPH variant, new propellant, and new projectiles with a maximum range of 70~ km.
They already have a mockup of the new gun barrel (which is 6 foot longer than existing ones) on a M777A2 and are moving it around to find out which combination of barrel counterweights will be the most efficient for mobility.
Attached is a CAD model of the M109A7 with the new ERCA gun. At this point...maybe the turn signal lights are original to the 109.
It'll probably be cancelled like every other US Army modernization effort though.
Re: SP and SPAA Developments
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