Is it new brass, projos, what powder...

If it's once fired LC, you'll need to full length size the brass. New would be best if you're starting out new on everything, plus once fired brass out of an M2/3 needs to be checked carefully. A lot of it is junk because most of the gunners leave the head space loose so that they fire all the time. The problem with that is the gun will stretch the brass, so much that it will ruin the brass on the first firing. There are ways to check the brass to see if it has any problems.

Projos, new there aren't any issues but pull down have to be resized, CH4D.com makes a die for resizing pull down .50 projos. Just lube them up and run them through the resizing die twice, that way you can be sure that they're sized correctly.

Powder, you can use pull down military surplus and it'll be fine. If you want a little better, buy some off the shelf powder, H50BMG is gone at the moment, Hodgdon might bring it back, no one knows right now. There Vihtavouri in a couple different flavors, 24N41 and 20N29, great powders and come with a high price. There's also Reloader 50 by Alliant, I haven't used it but I've heard that it works well and gives good results. There's 1 or 2 more out there, just punch it into Google and they'll pop up, load a few rounds with different powders and different charges. That way you can figure out what your gun likes and gives you the best accuracy. Another note on loading and powders, you don't have to max them out, start low and work up. Using Viht, 222grs gave me great results and kept AMAX under MOA at a 1000 yards when I shot matches. Plus you'll also want to play with the overall length of the rounds that you load up, that will help you get a tad more accuracy.

Then there's prepping the brass, as you know from reloading that prepping the brass is another way to get a tar more accuracy out of it and the most important is repetition, keep everything the same when you find the load that gives you the best results.

@Saddler

Have you guys tried turning your own on a CNC screw machine? A couple of guys that I shoot with had a run of about 25K done years ago out of brass in the shape of M33 projos. They came out about 100 grs heavier and out shot standard M33 like night and day!

I know there are quite a few .50 shooters on the other side of the pond, if enough guys pitched in and did a run big enough, you might be able to get them made cheap. Might even help if one of the shooters is a machinist with access to the right machines.

I think I still have some loaded ammo with those bullets in them. I'll have to check and post a picture of them, if MrBen sees this post, he might have some loose ones laying around his shop that he could post a pic of.

As for starting loads, 215grs. is a good starting load for most powders. Surplus pull down powder you might have to go a little lower, down to about 205 and check for any signs of over pressure.

When you start to increase the charge, do a few rounds at a time and check/watch for over pressure signs. When you shoot them, check for accuracy also, you'll find that you don't have to max out the charge to get good accuracy.

Have fun and be safe, post some pics of how your reloads are doing.

***** Thanks Kalash for the info on Reloader 50 and heavy bullets, I'll be sure to remember that and pass it along to other shooters.*****

No, that lead is just a small plug and then you have a copper jacket over a steel core.