The .400 calibre rifle is the perfect beginner's double IMO, and may well end up being the last double you ever own too! Provided you reload, the chambering will give you every satisfaction I'm sure. I have hunted with one on the 3-inch case for many years, and exclusively for several years, and never found it wanting on buffalo and boars.

Bore-size is important in the .400, both .408 and .411 projectiles are available, if the size is other than either of these, good jacketed bullets may be a little harder to source.

Try to shoot the rifle for accuracy and regulation before buying, or arrange a money-back guarantee if it doesn't shoot. The worst is one barrel group significantly higher than the other on the target, this normally requires re-regulation.

Good luck with it, I hope it falls in your price-range, they are marvellous things!