Re: useing blc-2 powder....
Well, I'm getting 8723 psi muzzle pressure predicted with IMR 4895 and Winchester 147-gr bullets. Had to correct the data file as it didn't have the bullet length or boat-tail dimensions.
In 55.5-gr chambers, it's mild for pressure but gets the 2800 fps at muzzle that I think it needs to be about 2750 at 78 feet like Uncle Sugar's ammo is supposed to be.
So, ASSUMING that the NATO specs for M80 Ball centered around that muzzle pressure out of a 22-inch barrel, it would be like to know the tolerance (high and low range) allowable.
Your 26-inch barrel takes the predicted velocity with that load up to 2900 fps, and the muzzle pressure down to 7185 PSI, and the barrel time of the bullet about 0.117 milliseconds longer.
Will that "extra time" before pressure release to open air affect a G3 system's unlocking, or the residual pressure in the chamber as extraction begins? Heckifiknow. If you can find a timeline of the firing cycle of your HK system, then have at it.
I can tell you that a predicted 2900 fps charge of Ball-C(2) powder models to 7305 PSI muzzle pressure, and has a SHORTER barrel time than the 4895 load, so the paper answer is that with the 147-grain bullet, Ball-C(2) might be easier on your HK system than 4895 loads.
Go up to a Sierra 190 MK, and the muzzle pressure remains lower than the 4895 load using M80 Ball bullets, and barrel time only a small bit longer than the 4895 load.
At this point, call Hodgdon's people and ask them if there are any cautions about using that powder in HK semiautos in .308. If they say no problem, I'd believe them.