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About 10 years ago, a Gun Club held a .303 shoot. I used a Number 1 Mark III rifle, with cartridges loaded with Remington 123 grain bullets. There were six events, two each at 100, 200, and 300 yards, and there were something like 38 shooters that showed up. We shot standing and kneeling at 100, sitting and prone at 200 and prone and a 15 round rapid with a one minute time limit at 300.
There was a First and Second Prize for each event, and out of the 12 prizes, I ended up with 6 of them. Not too bad for a guy who was 60 years old at the time, using those light 123 grain bullets. As to accuracy, there were two Firsts at 200, a First Prone at 300, a Second Rapid at 300, a First Standing at 100 and a Second Kneeling at 100.
I would say that the 123 grain bullet CAN be accurate in the .303 British, but you have to develop a load that suits it. The Remington bullets ran .311 diameter and were designed with the SKS in mind, but I used a reduced load of IMR-4895 that gave velocities in the 2200-2300 FPS range.
If you want to use cast bullets, try 13 grains of Red Dot Shotgun Powder. This is referred to as "The Load," and was promoted by C.E. Harris who experimented with Cast Bullets and wrote articles for the American NRA.
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