Imo the Beldum catch rate actually based on nintendo pokemons(?) is a bit to low. 0.4% on full hp for a stage 1 pokemon without evolution. We can't false swipe him coz he uses take down move that deals him recoil dmg, so that makes him harder to catch. Even with sleep he has 1,56% for catch. That means most of the time he will kill himself with recoil or struggle if we use a normal pokeball, Even when we use ultra balls we still have +/- 2,5% catch rate. This pokemon is quite rare anyway so when we encounter him and and he faints by strugle or recoil it's really annoying. 
I suggest to give him at least 5-10% catch rate from the start.
Games should give fun for people not make them nervous, and frustrated.

Hello, -1 as it is not impossible to catch, just time consuming but can easily be caught with patience and strategy.

 

Method here to catch him with a 100% success rate.

I don't say it's not imposible. Anyway it's time waste. And my and i think many other players time is immportant. Maybe some no-lifes like methots like that. Spam 20+ pokeballs for one beldum who is 90% bad iv, abilities etc 😉 

if you think its a waste of time simply dont do it, there are other ways to acquire beldum such as bosses and purchasing from other players 

Its catch rate is 100% for me, always, so no need to change at all.

 

Think more of the method & you'll eventually find that.

 

Small tip for you: don't even think of using Pokeball for it