I've used a bunch of bulk lead core 62 FMJ bullets.
Leftover Winchester and Federal bullets, along with commercial Hornady, Speer, Armscor amd Prvi.
Armscor and Prvi lead core 62 grain were terrible in accuracy, even though 55 grain FMJ and 62 penetrator from Prvi had decent accuracy.
Then the American ones, Winchester wasn't great, Federal was so-so, but Speer and Hornady were best and pretty good.
When Speer changed owners, Speer quit selling .224" 55 grain and 62 grain FMJ bullets, along with quitting .308" 150 grain FMJ and .310" 123 grain FMJ bullets.
This was said to be due Speer was buying their FMJ rifle cartridge bullets from Hornady and the new owner didn't want to buy bullets from a competing bullet maker.
The Hornady bullets have always been the most accurate of the 62 grain lead core bullets I've loaded.
They are not in constant production.
Hornady makes runs for their own commercial sales and also makes batches for contracts with other companies.
There are periods that they aren't available though.
IMR-8208 XBR was developed in Australia to load 62 grain penetrator bullets and meet NATO specs in accuracy, velocity and gas port specs.
They also use it to load export military 55 grain bullet ammo and current Australian 5.56 cases have the same capacity as Lake City cases, unlike older Australian 5.56, with their smaller capacity.
Australia quit making their own primers in 1999 and now imports American CCI primers for 5.56 and 7.62 and imports German RWS primers for 50 BMG.
The original reason Australia developed IMR-8208 XBR was because their SAS wanted to use M4 Carbines, along with available M4 optics and accessories and their original 5.56 ammo didn't meet the gas port requirements of the M4.
It's a pretty specialized powder, as it isn't easy to meet NATO specs with a single base powder and most other countries use a double base powder.
It also overlaps the gas port specs of some non-NATO spec 5.56 firearms, such as the Steyr AUG, so it has a wide range of functionality.