Black Hills red box 69 grain vs IMI razor core MK262 77 grain

Just wondering what is more accurate in general. 1/8 LW barrel.

Every gun is different. All 3 have potential. You will not know which your gun likes until you try them all.

Another way to look at this is to see if your needs are met by the differences when comparing apples to apples.

For example, BH 77 versus IMI 77, or other.

When you compare for example, PRVI match ammo to BH with the "same" specs, the PRVI is okay but in general is a little cheaper and performs just a little lower.
For many, that means they run both and use the cheaper stuff when not keeping score or when they feel like it.

You will not be let down by IMI, they make good ammo. The only way to know is to run some samples. The good news is you have good choices.

IMI 77 worked better for my set-up.  I was pulling sub-moa with the razor core, yet the BH 69GRN were anything but sub-moa.

I was using a BCM 410 SS 16" (1/8 Twist)...

My two cents, buy both and see what works best for your set-up.  Good luck!