Following a recent discussion on Reddit regarding how poorly the MS-18E Kampfer fared against the Alex's 90mm gatlings... I thought it would be appropriate to see just how the standard weapon of the GM series may have fared...
The HFW-GMG-MG79-90mm GM Machine Gun was the essential anti-Mobile Suit machine gun deployed in the One Year War. As a 'system weapon', different parts could be combined to create the GM Rifle, and the GM Long Rifle. (TL: The HFW-GR·MR82-90mm GM Rifle and HWF GR·MLR79-90mm Long Rifle, respectively.)
When used against either Super hard steel alloy and Titanium-Ceramic alloy armor materials, the weapon has the power to easily penetrate either.
This weapon was also seen being used by the RX-78-GP01 during the Torrington base Gundamjack incident.
Source: Master Archive Mobilesuit RX-78GP01 Zephyranthes