Steel frame, mudguards and 10 kilos/22 lbs dead on. 42:16 1/8 drivetrain. Fantastic ride. Will be replacing with a lighter and shorter stem and nicer bars. But sub 20lbs, even without the mudguards will require a new frame or carbon forks. For reference, I have a quote of £1200 from Burls to make the same frame in titanium. And I REALLY like the kona steel forks.
My 531c track/hill climb bike is 18 lbs. With front brake. But it is a small frame, runs tubs and has a very steep head angle, with no bottle mounts. It’s not exactly a relaxing ride!
To be honest, getting under 20lbs with something that 1) is not a track bike and 2) is made of steel is not easy. A langster with Al frame should be OK. The upgraded wheelset and tyres on my Kona still come in at about 2200g because track hubs aren’t that light.