I've played with a few different powders in the .303 Brit. I don't think you can go wrong with any of the powders listed. I think my preference is for IMR 4895 / H4895 (Not the same powder but similar) for a 174gr load.

When loading for the .303 Brit (I'm assuming you have a Lee Enfield SMLE) there's are few things to pay attention to.

1. The SMLE action is inherently springy and this can stretch your brass, particularity just in front of the web of the case. After a few cycles of reloading and shooting you'll begin to see a ring appear. What it isn't obvious is that inside the cases you are getting thinning of the brass where the visible ring occurs. Eventually this will lead to a case head separation. I use a small pick to run along the inside of the case and if I can feel the spot where's it thinning with the pick, then it's time to throw it out or to relegate the case for my "mouse fart cast loads"

2. Bore Diameter is important as they can very widely between .310 to .314 in some cases. Using a soft lead ball to slug the bore and have an understanding of what bore diameter will go along way in selecting the proper diameter bullet for use in your rifle.

3. Surplus Lee Enfields were used in competition shooting in in the years following WW2. They are capable of good accuracy if one knows how to accurize the Lee Enfield. If you'd like to get the minute of "Playing card" using some of the techniques these old timers used should get you most of the way there. There's a few books on it that I have on my book shelf and are readily available on Amazon.

4. Honestly, I like the PPU brass for this caliber. I have no idea who makes it for them or if they may it for themselves but it's worked for me. I haven't ever bought just brass.

5. For accuracy, the 174gr SMK does well for me. My rifle shoots about 2 minutes of playing card. I hope to bring that down by tightening up the stock.

6. Another thing you might look into is cast bullets. I have a Lee Mold and cast 150gr pills. 11.5grs of unique will drive the bullet to ~1500fps. It tames the rifle and is way more fun then you could image.

7. The throat is quite long so trying to seat off the lands is pretty much impossible. Even if the bore is quite new.


Hope that helps.