Gas operated guns require powders that produce a pressure curve which fairly closely matches what the gun was designed for. Too fast will beat the gun up, too slow will short stroke the bolt(no ejection). H-1000 is too slow and IMR 4350 may prove to be also. Sad fact is that optimum loads for the .270 may never work in a gas gun. You have to load for the gun- not for velocity.
I had a nice Belgium Browning BAR in .30-06 and that's why I sold it. I realized I could never load it to the cartridge's full potential. Proper function and maximum accuracy demanded moderate loads. Not really a problem, but at the time I wanted top velocities so I got a bolt gun.
Most likely it's something that we cannot buy. That is, it probably is a non-cannister grade of one of the IMR powders, your guess would about as good as mine.
Each lot of powder is different than another, so for us reloaders, they mix up several different lots to give us a standard lot to use. For themselves, they do closed bomb testing which determines for them just how to use the non-cannister lots for their ammo.
.270 Win. factory loads - downloaded for Remington autos
The .280 Remington was originally introduced to give the autoloader line a .270 like cartridge. The .280 operated at lower pressure with faster powders to accomodate the pressure curve needs of semi-auto rifles.
Remington's later decision to chamber the .270 in their autoloading line, soon resulted in rash of jams. The undersize extractor would rip through the cartridge rim in the overdriven rifle actions. A prime example of the downloaded status of today's "regular" factory ammunition is Winchester's 130 Power Point .270 ammunition, which barley generates a chronographed 2775 fps out of a 20 inch barrel.
Bolt action enthusiasts can of course use "light magnum" type factory loads to get the original .270 ballistics. These loads will overdrive an autoloader.