My personal research has only been on M1918 and M1918A2. I know nothing about the M1918A1, but it APPEARS to be an M1918 with a bipod stuck to it. If so, it would be lighter than the M1918A2. If it’s lighter, but other aspects are basically the same, then it also will experience more recoil. So here should be the trade-offs that I perceive…
M1918A2
-Heavier, so slower to bring to aim or to run with (a bit bad)
-Heavier, so lighter recoil whether standing, crouched, prone, or what have you (very good)
-Smaller u-notch sights instead of aperture, in theory better for target shooting but allegedly more difficult to use in stressful combat situations (you be the judge)
-Altered magwell and/or mag release allowing for faster reloads (good)
-Slow-auto instead of semi-auto (again, you be the judge, pretty easy to get off single shots on slow-auto so for some that would be a totally negligible difference)
The M1918A2, compared to the original WWI M1918, is made several pounds heavier due to the bipod (which as far as bipods go I hear it’s pretty bad), the thing on the buttplate that you can fold up to allow it to rest on top of your shoulder, (a literal “Shoulder thing that goes up” lol), a blockier magwell and/or mag release to aid reloading, and a carry handle that is necessitated by all the other stuff.
In my opinion, the M1918 got it right and the M1918A2 is ridiculous. Arguably the worst LMG of WWII, and abandoned any notion of ‘automatic rifle’ once it added all that weight. The original M1918 was at least only around 16lb unloaded as I recall! With the heavy M1918A2, you’re stuck with 20 round mags, you can’t swap the barrel in case it overheats, the sights are smaller and more difficult to use, and the bipod uses friggin’ WING NUTS. I’m sure it served the soldiers well for those who were issued it, but really, I mean the MG42 is only around 6lb heavier than the M1918A2, but closer to 10lb heavier than the M1918. The BREN has more usable sights, even though they do obscure vision on the right side, and the top-mounted magazine makes for easy and fast mag-swapping for the assistant gunner, plus 50% more magazine capacity in the jump from 20 rounds to 30 rounds.