My C++ Knowledge is not great (I`m still learning) but you should not need the const at the beginning, the blueprint wont be able to change the value as it is read only.
I think you should have in the .h file:
UPROPERTY(BlueprintReadOnly)
float ConstantParameter;
Then in the .cpp:
ConstantParameter = 924375700.f;
Hope that helps if im incorrect sorry just a suggestion 
Also you may need to put float in front of ConstantParameter in the .cpp im not sure