I
really didn't want to bring back a two-years-old topic, and didn't want to be a turbo-nerd here, but Invasion rifle isn't PGM either. They do look similar, sure, but what Invasion really uses, is
EDM Arms Windrunner or
Nemesis Arms Vanquish. Both are available in .338, and both have features of Invasion rifle, like collapsing stock and bipods under receiver's front
This one here is
Windrunner, for example:

Furthermore,
Windrunner rifle was later used as a base for
M200 Intervention, so Norman's original choice and KcholoStrike's suggestion weren't too wrong either
As for 5-rounds capacity... Well, Invasion wasn't exactly the most accurate mod. They had Beretta the size of Desert Eagle. Although, there is 12-rounds Beretta 96 for .40 S&W
Not that this forum is still being active, so i don't think this would really bother anyone. By the way, the IR pistol is MK23, but with USP textures