.h
UPROPERTY(EditAnywhere, Category = BulletDecal)
UDecalComponent* DC;
.cpp
DC = CreateDefaultSubobject<UDecalComponent>(TEXT("DC"));
DC->FadeScreenSize = 100000.f;
FVector BulletHoleSize = FVector(3.5f, 7.f, 7.f);
DC = UGameplayStatics::SpawnDecalAtLocation(GetWorld(), BulletHoleDecal, BulletHoleSize, HitResult.ImpactPoint, HitResult.ImpactNormal.Rotation(), 5.f);