New Remington 300 BLK UMC Subsonic ammunition.

[felixXJ]

My guess was 5744 at a glance. Likely, as you say, a permutation

[300Blk]

Actually, I think, but if someone knows more than me they can correct me, powders that ammo companies use have more lot-to-lot variances than powder sold on shelves.

This is because the loading companies control lot variances by loading to a pressure/velocity using fancy test equipment and reference barrels rather than using a fixed-mass powder charge like home loaders.

[Dr.Phil]

Actually, I think, but if someone knows more than me they can correct me, powders that ammo companies use have more lot-to-lot variances than powder sold on shelves.

This is because the loading companies control lot variances by loading to a pressure/velocity using fancy test equipment and reference barrels rather than using a fixed-mass powder charge like home loaders.

This is my understanding as well.
Large ammo manufactures reset their powder charges with every new lot of powder.
The charge is determined by pressure not velocity.

[300Blk]

By pressure and velocity, as opposed to charge weight.

Pressure and velocity, as far as I know, are pretty much the same thing.

[Dr.Phil]

By pressure and velocity, as opposed to charge weight.

Pressure and velocity, as far as I know, are pretty much the same thing.

I don't disagree.
Those manufactures are just use pressure as their unit of measure as opposed to using velocity like most home loaders do.
And of course, those manufactures use that "Fancy" equipment you spoke of to measure said pressure.