I asked one of the lads at the range today and reckons he uses 75 grain of Swiss powder at 200 yards.
If your bullets are dropping short then it is either because your powder charge is too small or the bullet is not sealing the bore, or both.
If you have one of the bullets that came with the rifle measure the diameter. If you can get the same type of bullet you should be ok. But bear in mind not any bullet will suit your rifle.
You can have two idendical rifles and both can shoot differently with the same bullet/load.