New US Army SPH M1299 based on the M109 series. 155mm 58 caliber barrel. The XM1299 is part of the Army's Extended Range Cannon Artillery (ERCA) program.
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I wouldn't be adding it to the game just yet. The US has a long history of cancelled projects.
During a firing test Yuma Proving Ground in Arizona in March 2019, the M1299 gun nailed targets with pinpoint accuracy at a range of 62 kilometers, offering a greater range compared to the M109A7 Paladin which has maximum firing range of 30 km and for 40 km with the M982 Excalibur guided artillery shell for the M777 light towed howitzers.
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The M1299 tracked self-propelled howitzer has a fully-automatic ammunition loading system. It loads both projectiles and charges. This automatic loading system increased the rate of fire from 3 Rounds Per Minute (RPM) on the M109A7 to 10 rpm.
The M1299 continues the use of 155 mm caliber of ammunition but it will use new XM1113 rocket-assisted artillery projectiles. In June 2019, General Dynamics Ordnance and Tactical Systems (GD-OTS) awarded a contract for Prototype and Process Development for the 155mm XM1113 Rocket-Assisted Projectile (RAP) round.
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The XM1113 RAP uses rocket technology to deliver greater thrust to the round when compared to its predecessor, the legacy M549A1.
This will enable current U.S. Field Artillery 155mm Systems to fire the XM1113 RAP to a range of 40 kilometers, a 30% increase from the M549A1.
When fired from the planned future Extended Range Artillery Cannon (ERCA) [aka XM1299], the XM1113 will achieve ranges out to 70 kilometers.