I was a 13A00, FA Officer, spent most of my career doing Fire Support, 2 heavy and 1 light assignment (11th ACR, 1ID, 25ID), but was a cannon PLT LDR and Battery CDR, as well as Co. FIST, TF and BN FSO and BCT FSO.
I used to feel bad for the M110 8" guys at Graf.
Most of the M110s I saw didn't have the "crew cabs" so the guys rode around exposed on the tank trails, summer covered in dust, winter snow and sleet. I was a Howitzer Battery LT with 1/11th ACR at the time. We had M109A2s and a couple A3s (155MM). I think we actually got to shoot more, just a less expensive round.
The M110s were held in GS (General Support) BNs and usually employed for counterfire due to their longer range. Back then some of the FA Brigades were composites; 109s, 110s and Lance Missile BNs, I was still in when they fazed the 110s and Lance out for MLRS & later HIMARS.
Technically it's a "Howitzer" not a gun, the old M107 175mm was a "Gun" (looks like an M110, same chassis, long skinny tube), it's all about tube length, velocity and trajectory. The "guns" had a higher PER (Probable Error Range), which made them not so suitable for Danger Close depending on friendly trace in relation to the gun/target line.