Big enough for BMG and 600-700 NE, also for BMG wildcats
and derivitives.Need a 8.2 inch diameter bolt, and 5.5 inch stroke,
with a 1.25 in barrel thread.Ruger builds strong 77's , as I can
attest to as I screwed up once with my 458 wildcat and shot a
load out weighing 3300 grains at 1500 fps, generating 150,000 psi
and action stayed together.Brass didn't blow out.Brass expanded and locked up bolt,We took barrel and brass out with lathe, and rebarreled
after testing reciever and it works great.We had longer barrel there at the time planning to change to test cartridge with a longer barrel ,so only
a couple days were lost.A big action in 77 style would sell like hotcakes,
and it would be the most affordable as they use investment casting
process which save big bucks.Ed.