I loaded up some ammo for my sporterized .303 Lee Enfield for deer season as well. I used a .311 diameter 150gr Sierra Pro-Hunter with Prvi Partizan brass, 38 grains of H4895 and a CCI LR primer...I hope they shoot as good as they look. :)
For our .303 Lee Enfield rifles(mine is sporteized and my boyfriend's is full military dated 1944) we use winchester or remington brass, 125 gr sierra pro hunter with 43 grains of IMR 4064, 150 gr sierra pro hunter with 43.2 grains of IMR 4064 and 174 gr Hornady with 40.6 grains of IMR 4064. They work really well and I love making them. I love my .303 and my boyfriend loves his dream gun(he's wanted on since he was in his teens). They are great hunting guns.