Hey ya'll. I'm just looking for some data on loading 303 Brit with 150 grn hard cast gas checked bullets. I need powder recommendatons (type, amount, etc). Currently I have only Varget and IMR 4831. Any help would be greatly appreciated.

Either will likely work okay, if you find a good charge weight for YOUR rifle. Where I would suggest starting is not with the powder charge, but with your rifle barrel.

In .303's bore diameter can vary widely. Some are as small as .310", while I have one friend in England who reports his groove diameter is .317" !! So, for starters, you should probably either "slug" your barrel, or make a casting with Cerrosafe of your bore diameter. It will definitely make things easier to know what dimensions you have in hand.

For easiest accuracy, I believe it is important to make your bullets as close to the same diameter as your rifle's throat (leade) diameter as you can, while still being able to remove a loaded round without leaving the bullet stuck in the throat, EVER!

After that, I would pick a velocity I wanted to achieve, and would select a powder which would give me about that velocity, and low pressure signs, with the case full of it.

If your rifle has a bore diameter not exceeding .313", you might want to start with the Lyman 314299 mould which was said to be designed for the .303 British. (It was designed many years ago, and was originally called the 311299, even though it was producing .314 diameter bullets even when it was nominally a .311" mould.) It throws a 185-195 gr, bullet depending on the alloy used, not 150 grs., but works well in many of the SMLEs.

But, be aware that to find a bullet your rifle really likes may require the purchase and/or trial of 3 or more different moulds and a variety of different diameter lube-sizing dies... A number of different lubes may need to be tried in your rifle too.

Successful small and medium bore cast bullet shooting is not something to be approached casually, except by the very lucky in life. It is normally several times the work of shooting jacketed bullets, both in making bullets and in finding the combo your rifle really prefers.

Good luck.