ACII means artillery carbine mark II. As Douglas states, the date for a MK II shouldn't be 1889, so look carefully at the stamping. The markings certainly sound valid except for that date, which hopefully is just difficulty in reading the stamp.

As to ammo, these of course were designed to fire standard Brit .303 ammo and have done so for over a century. As to how kind that century was to your carbine we can't say....but stress is cumulative and 100+ years is a long time. Of equall consideration is that these are fairly light firearms with less than modern ergonomics.....meaning they have a fair felt recoil. While I have a considerable stash of MilSurp .303 and commercial loads (and have shot more than a few rounds through my Martinis), I now prefer handloading for my older .303 firearms using nice mild cast loads. Easy on the firearm, easy on the shoulder......and at today's prices, easier on the wallet.