What he actually says is: "Some months previously I had been to Calcutta on a short visit and one morning walked into Manton's, the gunmaker's shop. On a glass showcase near the door was a rifle. I was looking at the weapon when the manager, who was an old friend of mine, came up. He informed me that the rifle, a .275 by Westley Richards, was a new model which the makers were anxious to introduce on the Indian market for hill shooting. The rifle was a beauty and the manager had little difficulty in persuading me to buy it on the understanding that if it did not suit me I would be at liberty to return it. So when I set out with my village friend that evening to shoot his jarao with horns as big as the branches of an oak tree, I was carrying my brand-new rifle.

...The rifle I was carrying was sighted to 500 yards and guaranteed to be dead accurate..."

Note that this Westley Richards .275 was sighted to 500 yards. I believe he acquired this rifle in 1909 or even 1908, since he started the Panar leopard hunt in 1909. He hunted with another .275, a Rigby, which may be the one that was sighted to 300 yds. This may have even been the presentation rifle!

The rifles he mentions in his hunting stories are:
1. Martini Henry .577/.450
2. Jones action .500 Modified Cordite double (ref. Champawat Tiger)
3. Jeffery 450/400 double
4. Westley Richards .275 (ref. Temple Tiger, sighted to 500 yds., acquired cir. 1908 or 1909)
5. Rigby .275 rifle sighted to 300 yds.(ref. Talla Des Tiger, acquired cir. 1908 or 1909; this may be the presentation rifle)
6. .450 (double?; this, may in fact, be the Martini Henry .577/.450)

So which .275 did he get first, the Westley Richards or the Rigby? I don't know, but probably close together.