The factory produced them with this style of grip cap, (and folding sight), but with a black hard rubber style cap on the end. Someone has modified it, I would imagine. The rifle would have been first proofed in Vienna and then reproofed in England. NPv means Nitro-proof Vienna. The Austrian proofs are probably mostly hidden inside the stock mortice along with the year of manufacture. Something like 656.23 will mean the 656th rifle proofed in Vienna in 1923, for example.

Ammo making can be straight forward, using 8x57 rimless. However the base can be a little large for the Mannlicher chamber with some brands of ammo and some chambers. These base diameters vary between makers, so if there's a problem, a .001" vernier will help sort out suitable brass. Don't use 8x57 Mauser loading data, of course.

The second sight should be a few thousands of an inch different in height to the one on the rifle, so if you find the rifle not shooting to point of aim, an exchange may help. The vernier will suggest to you the amount of change; just divide the target distance, (presumably 100yds = 3,600 inches), by the distance between the front and rear sight in inches, so you then have a ratio. Multiply the difference in sight height between the first and second sight by this ratio and you should pick if it's going to raise the point of impact at the target end by the desired amount. The tang sight also has 2 settings so you have options for longer range as well.

Woodleigh make a nice round-nose that apparently suits this rifle, (i.e. they feed well and being the right weight, they regulate to the rifles sights). I found and loaded some but I haven't used them yet. That might change soon.

BTW, my gunsmith filed down the face of one of these sights. He did a great job, so mirror like that on a fine-bright day I couldn't see it against the target. So I blackened it with smoke from a small spirit lamp. Also, I use a small diopter sight sold by Merit that sticks on my shooting glasses and helps bring sights and targets into good focus for older eyes. If you want really tight groups with open sights, it's very helpful.