Any commercial 6.5x55, will work fine in the Agb42B.
Just keep in mind, these rifles were issued with a parts kit, including extractors, firing pins, springs and plungers.
I had a problem with the very first one I owned, that was from the first batch that came into Canada. International out of Montreal, was selling bulk cases, loaded with a very fast flake powder and wooden bullets. They included enough #44 Bofors powder (imr3031) and 140 grain pulled bullets to reload them with. Good stuff, cheap but the primers were corrosive. Not a big deal, just a pain in the butt with the Ljungman system.
Anyway, to make a long story short, I followed the loading instructions that came with the package and had a Kaboom. It blew the mag out of the rifle, along with the 8 rounds still in it down against my leg. Damn that hurt. I had a bruise that went from my hip to my knee, about 8 inches across.
The rifle was undamaged, other than a small crack infront of the mag well.
Called the people at International and they asked me to send the rifle back on their dime and by the way offered to pay for any damages to myself and if nothing was obviously wrong with the rifle, even take back the rest of the package.
After about a month, they sent me an as new rifle and explained that the first rifle had the firing pin protruding to far and as it brought the cartridge into battery, set off the primer.
This is one of the problems with the Lungman system. Other than that, they like the pressures to be around 45,000psi and hanldle it quite well.
When the Rashid and Hakim were made, utilizing the Lungman design, they included adjustable gas ports.
One thing I never did find, were any of the full Auto M42C models.
Many of the rifles that came into Canada are marked as the C model but it doesn't look like any full auto parts were ever installed.