I'm trying to reload some MOA or better ammo and looking for recipes. Would like to be able to shoot  600 yards (the max distant at my range)

H4895 power
75gr hornady HPBT
18" 1:8 barrel

Hogdon shows 22.5 gr up to a max of 24.5gr

However lots of internet searches are saying that with h4895 needs loaded close to max to be most accurate. 24.2gr seems to be common. And instead of 2.250" several say 2.245" (if that matters in this case)

What are some pet loads for h4895 and 75gr .223?

As you mentioned, you might experiment with seating depth, but I use 2.26" or just a hair under. Best AR load I've found with the Hdy. 75 Match HP has been 24 H4895 and CCI400 primer. CCi450 or Rem. 7 1/2 would also be worth trying. This is an accurate load, but the accuracy has always been slightly behind that of the Sierra 69 MK or 65 GK to 200 yards, about as far as I shoot any AR.

I've also tried TAC powder with the 75 Hdy., but I've found H4895 slightly superior for accuracy.

The OP needs to let his gun do the talking not copy cat reloading.  Do a proper load work up and the your gun tell you.
I would say TAC would be a better option.

23.5gr is my max and high node with moly'd 77gr SMK. Been a while since I used H4895 with 75s, but 23.8 - 24.0gr should be close.

I'd check 23.0, 23.5, and 24.0gr.

Set it at 2 250" +/- 0.007". If the best node has a mean radius of 0.4-0.5 MOA and velocity SD under 20fps, maybe try 2.230". Some have reported a pucker when doing that.

OP would rather start from known loads to narrow it down rather than start from such a wide range.

I'm guessing you don't have any load data for the h4895?

Hornady's 75 grain hpbt or Sierra's 77 are excellent magazine fed bullets, but they don't work as well as Hornady's A-Max 75's or Sierra's 80's seated just shy of the rifling for 600+ yards.

With that being said I would start around 21.5 grains of H4895 and increase no more than .3 grains at a time up to 23.0.

Shoot the load that groups the tightest in your rifle. I look at 2550 fps as the low end from a 20" barrel. I feel anything faster than 2650 fps is too fast from a 20".

If you want to just go shoot try 22.5 grains of H4895 with 75/77 bullets seated at 2.250" to 2.255".

Thanks for your help guys.

Looks like I'll load some 22.5, 23, 23.5, and 24 and go try them out.

I'm sure all of them will be more accurate than me....