I really liked the La Longue Carbine in my first playthrough and even though I have yet to get an AMR in my 2nd hardcoe playthrough just seeing that the .50 caliber bullets weight 0.5 makes me not want to get the gun...
Another thread earlier asked about the weight ratio and use of the AMR..
I'll just repot my ol' boring fence post from there..
For one fight against a small robot army I took it and enough ammo out from the
bag of holding beans ED-E's inventory.
It raised my weight by a third +, if you plan to use it as a main weapon, take weight related perks if on hardcoe or you'll suffer.