To bowl out swingers you need more of a side on action
=/ No you don't. You can swing the ball from a front-on, mixed or side-on action. The key to swing bowling is wrist position and seam presentation; as well as the ball, wind direction and atmospheric conditions. If you get your wrist behind the ball and in a good position, and then get the seam coming out straight you'll swing the ball. The direction your feet point, poses no direct correlation to the amount of swing, certain actions can assist swing bowling, but you don't
have to bowl side on to swing the ball.
Quick couple of tips to help achieve both the wrist position, and the seam presentation. I'll start with a great tip for seam presentation, which I learnt from Ian Pont. You see spin bowlers standing with a cricket ball and they'll be constantly spinning the ball in their hand, as it gets them used to applying spin to the ball, and gets their wrist used to the movements. Seam bowlers can do the exact same thing. You just need to hold the ball with the seam straight and then just flick the ball in the air, with the aim of keeping that seam deadly straight. If you practise enough you'll get it right almost every time. It then trains your muscle memory to release the ball at that correct time, to then get the seam straight. It does work, as it was something I used.
As for wrist position. I'm not really sure of any little drills to practise which can help with that, but getting a video camera out, and watching yourself bowl in slow-mo can help you realise what you're doing with the ball, and how you need to correct your wrist position. Here are a couple of pictures to demonstrate what position your wrist should be in:
Outswinger.........................................Inswinger
If you bowl with the new ball, you shouldn't need to exaggerate the direction of the seam quite that much, just getting the ball going down with an upright seam will extract movement. Also, a quick in-game tip to know if you're bowling with an upright seam is to see what the ball looks like when you get it back in your hands. If it has grass in the seam, then you had it coming out upright, if the side of the ball is scuffed, then you'll know you're bowling with a scrambled seam, and are therefore less likely to extract swing, or seam movement. Getting the seam straight, and then hitting the seam is one of the real keys to seam/swing bowling, if you can get that right, you'll be on your way to taking some wickets. Hope it helps.