Does anyone know the drop rate of the experimental kvm and sledgehammer because I can never seem to get one when killing rivals?
There is no official drop rates so its all speculation but the EXP sledgehammer is a reaper exclusive, rivals will not drop this.
Yeah so there the KVM drop rate seems to be the lowest of all in my epxerience. A while ago I think there was a bug about the reaper being unable to drop the KvM which was supposed to be fixed in the landfall update. Right now I haven’t seen a KVM from the reaper yet but two sledges. Back in the day I could prove KvM did not drop from reaper because there was an exploit that allowed to refresh the loot from the reaper after looting it and I did it like 250 times, but right now my sample size is like 5 kills so no representative numbers from me 
Well, the exp KVM is not just supposed to be dropped by a reaper like the sledgehammer.
After about a year in GZ I still did not get a sledgehammer, but about 10 klaucke, 8 shotguns, 6 kpist, 7 kvm, 5 pvg, 2 granatgevär and 3 ag4.
Just had one kvm right today from a lvl 4 prototype tank rival. It’s just random.
While a friend got an exp AG4 right after reaching lvl 25 with his first character, it took three more month for me. 
Again, from landfall update notes: Fixed an issue where the Experimental KVM59 was not dropped by Reaper