People keep saying this, but it's not remotely true.
Hornady makes an eld-x in 277 with a .536G1, though they really should made a better one.
Berger make's a VLD and an EOL with .518 and .662 G1 BC's respectively
Barnes makes an LRX and is rumored to make a better one. .46G1
Nosler makes the BT with a .56 and LRAB at .62
Sierra makes the TGK at .56
Badlands makes a SBD-2 with a .71 G1.
The only BC you can argue is low there is Barnes, but that's not different than their 6.5 or 7mm offerings.
Just curious, what other bullet manufactures are you wanting to put out high BC 277 bullets? Or is .5-.7 not high BC anymore?
I know you can get into the .7's with the 7mm stuff, but to push those heavy bullets at the same speeds you're talking a significant increase in recoil.
For that matter, some 338s and 375s have some really high BC's approaching 1.0.