As the US progressed into WWII, the M1918 "Schneider" 155mm Howitzer was gradually replaced by the M1 155mm Howitzer, though I understand the Schneider continued to see service throughout the war. The standard HE projectile for the Schneider (pre-war) was the M102 and for the M1 was the M107. I understand one of the differences between these two projectiles was that the M107 had a wider rotational or driving band. I could swear I remember reading somewhere that the M1 fired the M102 okay but there was some loss of accuracy as compared to the M107 due to some size difference (possibly the driving band?). Conversely, I thought I remembered that there was a problem firing the M107 through the Schneider due to some size difference in shell, chamber or possibly tube size? Now I can't seem to find any reference that suggests that there was any compatibility problems with ammunition between these two Howitzers. Does this sound familiar to anyone or did I just have a brain fart?
I ended up finding the answer that I was searching for in TM 9-1901 "Artillery Ammunition (1944) and indeed, there were compatibility issues. Here's an excerpt: Sub-paragraph (f) contains a somewhat confusing table but appears to indicate you may fire the M102 H.E. projectile in the M1 as well as some gas and smoke shells as limited standards. It does not indicate any use of the M1 projectiles in the M1917-18s. This is a scanned .pdf file that is difficult to "copy and paste" and I needed to make multiple corrections to the above "copy and paste" I quoted so it was legible. Above the table in (f) it says "To be fired only in extreme emergency with the shell indicated".
