Behind the scope mount is "NAT..." so yeah, it probably is a Nat'l Ordnance.
And don't worry, it doesn't actually look THAT rusty. But I'll definitely be cleaning it up ASAP. There's no pitting or obvious rust anywhere, thankfully. Bore is 9/10, tiny bit of patinated copper on the very end. I'll work my magic on it for 10 straight hours sitting hunched over a cleaning table at my nearest opportunity.
