Any load data I've found is rated for .223 Rem. Where can I find the higher pressure NATO spec. data?

You can't!  Are you and experienced handloader? Do you have a chrony?  If the answer is no to any of theses two questions I can't help you. If it is yes to all PM  me and we can talk as I'll not post info openly for dumb arse's to blow themselve up!

There is some 5.56 data on Ramshot's website.



For the most part, you will not find anything that is not SAAMI, aside from people telling you their recipes.





 

Ramshot publishes 5.56 data, but be forewarned:

It WILL shorten brass life, and if you don't know what the hell your doing, you may just shorten the life of a gun too.

You can load ammo much more potent than NATO ammunition due to bullet choices, so don't get hung up on the "I want 5.56 pressure" attitude.

SecurityForcesmember
  Yea I'd say they are definately pushing the evelope at Ramshot- the orginal Spec for the 5.56mm was 60000psi  with 55gr bullets!  Thats why the OP needs to have experience in reloading and a chrony.  If I used Ramshot TAC I'd back them loads off some to get below the 61000 plus PSI.     Even the Military has backed there load specs back  to 57000 psi now. I reload pulled 55gr FMJ very close to the original spec  which gives me  about 3100 ish out of my 16" AR .  Thats plenty of punch. When I had my 20" Colt they'd run alittle over 3200 fps!

Why push loads when I can get same speeds with less than military charges?

25.5grs of W748 gets me mid 2900's from 16" barrel and 55gr M193's.

I load this brass at least 5 times.

This. Do not try and reload to 5.56 pressures. It's not safe and you can achieve similar results with quality commercial powders. Plus the powders they use are in bulk and vary by lot and are also not very consistent. Commercial powder does too, but................. not like the surplus.

Accurate has a giant PDF on their website with 5.56

I reloaded some M855 using AA2230.

Plenty of discussion about this stuff in the Reloading Forum