I have no way to prove this theory, so you'll just have to belive me, or don't. Premier balls actually do have a little secret to them. From what I've been able to tell. Yes, they do have the same catchrate as normal Pokeballs. However, this is when the age-old myth about bashing the "A" or "B" button comes into play. From what I can tell hitting the "A" button rapidly highly increased my catch rate with the premier balls. I've caught all the legendaries in Sword using only the premier balls. Not only that, but I've also done it using a very small amount of them. The most I've had to use was somewhere around 27, but that was quite the outlier. Most legendaries I've been able to catch with ten or less throws, some I've even caught on the first try. Now, there is three things I should mention. Firstly, I've only ever used the "A" button. Secondly, I always bring their HP to exactly 1 (I recommend using Haxorus since he can learn false swipe). Thirdly, when I saw bash the button, I mean Flash level speed. The fastest you can possibly go, but not only that. You also have to time it, if you start to late or too early, the legendary will brake the ball immediately. Also, the speed at which you need to hit the "A" button increases with each twitch of the ball, and for the last one you have to seriously bash the button as if your life depended on it. So.much so that your arm should be tired afterwords. Again, this is all anecdotal, and in no way proves anything nor is it confirmed as a feature in the game. I also don't know if it applies to all Pokemon or just legendaries, cause I exclusively only catch legendaries with premier balls. If you're struggling to catch some legendary I would encourage you to try this, worst case scenario you've wasted some time, vest case scenario, catching legendaries just got a whole lot easier and quicker.