Welcome to the forum 119er, if you hang out here long enough you will learn a lot (I know I have).
I must say that is a very nice looking rifle. Thanks for posting pics. Demo is right in that it's a John Jovino rifle built up from parts (look for there import stamp on the right side of the receiver JJCo. NY NY) but they are nice rifles and shoot great. Just make sure the recoil plates are installed before you shoot her or you will end up with a split forearm.
I reload for a number of cartridges and 303 is one of them. I full length resize, but only because I have a large stable of Enfields. You will get better accurancy (most of the time) and longer brass life if you neck size only. Just remember which rifle it is for. There are some very informative post on reloading for the 303 on this forum, do a search and you will have several days worth of reading material.
You should be very happy with an 03A3, they are nice rifles and the M44 will get your attention on the range. At one time I had a 1944 and 1947 dated Russianicon M44 a Polish Made M44 and one of the Chinese copys. They are fun to shoot (HUGE fire ball with milsurp) and fairly accurate. Sold/trade them off over the years for different things, I should have kept one but.....