Ok this may be an obvious question already covered, though a quick forum search didn't turn anything relevant up, but…

What is the consensus on holy ammunition and powers such as telekinetic shield or catch projectiles?

Basically the group are about to fight the big bad, a seneschal for a powerful rogue trader house, who, in desperation, has donned a heavily modified Hand of The Dei Phage (my players are all rank 6, 7,000xp) the hand as described in The Black Sepulchre would have done nothing against the group. Here's the upped stats if anyone's interested -

Hand of The Dei-Phage

Boneslivers - 60m; S/2/-; 1d10+8 R; Pen:5; Tearing, Toxic, Corrupting

Claws - 3d5+5 R; Tearing, Warp Weapon, Hungry

Corrupting: if any damage is suffered then the acolyte must make a WP test, if failed the Acolyte suffers 1CP & 1IP and an additional 1CP & 1IP of each per DoF

Hungry: if any damage is suffered take a +10 Toughness Test or suffer one level of fatigue as the hand feasts on the lifeforce of the victim

However the hand is also having a very different effect beyond those listed above. The Seneschal is channeling, and being dominated by, the power of a daemon of Tzeentch (the aforementioned Dei-Phage who is using the hand to possess a victim to escape his bondage) and has been gifted a plethora of psychic powers and he's enveloped in a field of eldritch energy which acts as a force field.

Would you guys rule that sanctified ammo would ignore the eldritch shield and any psychic protections? I know it ignores the daemonic toughness thing but I'm not sure about the rest and after flicking through the Corebook, Inquisitors Handbook and Blood of Matyrs I found nothing concrete either way. Basically the group has a fairly min-maxed sniper who has 1 clip of santified bullets and, to be honest, I'm getting bored of every major npc getting his head blown off straight away. It's extremely hard to have a climactic fight if the baddie dies straight away but don't want to go too overboard and make him so tough the Acolytes are only a bad dice roll away from a TPK or have to resort to giving every NPC a forcefield!

Any advice is, as always, vastly appreciated :-)

While I'm not into the blessed/sanctified ammo thing if you're having problems with a sniper in the party being too overwhelming there are plenty of anti sniper mechanisms that could help.

We should assume of course that a min maxed sniper will probably have visual technology that minimizes natural obscuring effects such as smoke, minor amounts of cover, etc, and throwing blind grenades for no apparent reason while effective wouldn't exactly be in character. However have you thought about non natural visual effects? A being with the power level of this dei-phage could theoretically bend light, create terrifying winds, shears and unpredictable currents, and will probably be accompanied by warp lightning and such that would play hell with visual accuity, and that's just by BEING there, no less trying to mess up a sniper.

Even where you meet this creature would play a good role in reducing the sniper's overt dangerousness. Snipers in a dungeon crawl tend to be somewhat less effective as they can't(usually) sit out at long range and shoot people before they even know they're there. Same for snipers indoors, palaces, starships, etc.

If you're sniper has been effective recently, does the enemy know about him. The old "hey, when these guys are around peoples heads tend to get blown off" rumor can easily get around through the underworld. A sniper's day gets infinitely harder when someone knows he's coming. Don't want to put a shield on every baddy? How about the baddy hires three counter snipers and he has to take them out before they kill him just to get to the enemy? Sorcery can put a crimp in a sniper's day too. Hand of the phage need a body double? He can just MAKE one. How about the old illusory image technique? Dozens of ways to make the sniper waste his first shot, and even more to make sure he never gets a second. Ooh look you shot at my false image, how nasty that would have been if it hit me! Ohh look magical lightning just fell from the sky and melted your pretty rifle, isn't that so sad?

It seems to me a problem of tactics instead of equipment.

Hope this helps

P.S. I think psycannon rounds pierce shields, but I haven't heard a darn thing about blessed/sanctified ammo. I'm assuming they're two different things.

Psybolt ammo and blessed ammo are two different things; the former is nasty and messes psykers and daemons alike (and has the same bonuses as blessed ammo), while blessed ammo only negates Daemonic toughness.