I've recently hit a bit of a snag in my encounter design, and I hope the lessons I've learned can be helpful to others.
We've been running the same Only War campaign since the beta rules, and the PCs in my game are now approaching the 10/12.5k experience mark. They've picked up most of the obvious Talents and Advances for their chosen roles, and are now looking at branching into Advanced Specialties where appropriate. The main issue I'm presented with at this level of experience is that a combination of armor and Toughness have rendered at least two of the PCs almost invulnerable to small arms fire.
The party consists of a Sergeant, a Commissar, a Stormtrooper, and a Heavy Gunner. They're Vostroyan Firstborn, so everyone has a Good-quality Carapace chestplate, and everyone has managed to requisition Stormtrooper Carapace for their other limbs. Both the Stormtrooper and the Heavy Gunner have Toughness in the 60s, and it's with them that the issue arises. For example, in our latest session the Stormtrooper rushed into point-blank range to try to take out an enemy officer before he could vox for backup. Unfortunately for him, he missed, leaving him surrounded by 6 hostiles armed with autoguns with manstopper rounds. Of course, they opened up on him on full-auto, connecting with 15 or so hits. Even rolling well on damage, he was only brought down to Crit 2, and this is only the second time he's been brought into Crit in almost a year. He's probably going to pick up True Grit the next time they spend experience (the Heavy Gunner already has it), making him nigh invulnerable when he even takes Crit.
I certainly don't begrudge him his character's resilience; the PC's role as a bullet sponge has become a lynchpin in their tactics and has saved the bacon of everyone else in the party quite a few times. The issue I'm having is that it's becoming more and more difficult to contrive challenging encounters for the party. They've pretty much outgrown Troop-grade threats of every force they've encountered so far, and can stomp many Elites as well. Orks pose little threat given their overwhelming firepower (heavy bolter, plasma pistol, bolt pistol, and longlas are all in their arsenal); even if the Orks manage to get close enough, the Commissar is a power/chain-wielding blender, the Sergeant can more than hold his own, and the Stormtrooper can always Acrobatics out and blaze away at Point Blank. The Severan militiamen they're facing at present can almost be safely ignored, even with manstopper rounds. I'm looking forward to introducing Dark Eldar as the current conflict ramps up, but Wyches as written are completely useless, and even Kabalite Warriors are likely to be mown down without inflicting more than one or two points of damage. Of course, heavy weapons can always balance the equation; even the Stormtrooper would go down from one hit from an autocannon, but Dodge-or-die hardly makes for a fun encounter time after time. Accurate weapons work the same way.
Of course, I can always throw more guys at them (ramp up encounters from 10-15 to 30 or more), but it's both mechanically tedious and somewhat unbelievable from a fluff point of view. Vostroyans are tough, but they're still Guardsmen, not Space Marines. It's totally subjective, but it just doesn't feel right for them to be shrugging off shoota and heavy stubber rounds, and eating grenades for breakfast. Early on, the players were quaking in their boots at the thought of combat with Orks, but experience has taught them that they can survive encounters with three or four times their number and walk away at the end.
These thoughts could probably be better organized, but I feel like these are the main issues I've run into with mid/high-level play. Some of them (the Stormtrooper taking his +5s in Toughness) will probably be addressed by future expansions. So, here are some potential solutions and workarounds I've been considering.
To make Troops challenging again, I've been thinking of turning general issue troops into Hordes ala Deathwatch, and making others into heavy hitters/glass cannons. If the Hordes are limited to no larger than Magnitude 25 or so (even 15-19 seems fine for most) they shouldn't get too out of hand. They'll hit hard in the beginning (+2d10), but after a round or two they'll be down to +1d10, which will sting but isn't likely to be a one hit kill (at least with my party). These would represent large squad or small platoon enemy forces. The other sorts of Troops will be armed with special weapons (grenade launchers, plasma guns, big shootas, splinter cannons, etc.), and can probably only expect to get one or two high-damage shots off before they get toasted by the PCs. I consider the latter different from Elites in that they do not have high armor/Toughness or high Wounds, and don't really have any special abilities beyond damage dealing. If the Hordes get into close combat, I was considering just having them break down into their constituent units; the melee damage just seems too high, even as an abstraction.
Another option I've been considering is hitting them with squads of Elites in place of Troops. Instead of a squad of Kabalites or Wyches with a Wrack as a centerpiece, just hitting them with a full squad of Wracks or Grotesques. Mobs of Nobs for Orks, squads of Stormtroopers for Dominate. As long as they're defending or attacking a high value target, it makes sense for elite troops to be there.
Any feedback is appreciated.