Following on from the Armies in 5th post about Grey Knights primary shooting (psycannons and stormbolters) some discussion was prompted regarding psybolt ammo. Psybolt ammo adds +1 strength to certain bolt based guns including: assault cannons, autocannons, stormbolters, boltguns, bolt pistols, hurricane bolters and heavy bolters. There are a lot of cases of when this upgrade is acceptable and when it is not. This generally depends upon the cost and number of models affected. Let's take a look at some of the vehicle cases and then the infantry cases to help us determine when it's a viable upgrade.
Psybolt Ammo on Vehicles
There are two main auto-includes for psybolt ammo on vehicles: Dreadnoughts with autocannons/assault cannons and heavy bolter Razorbacks. If you're going to take Assault cannon Razorbacks it's a good upgrade on them as well but they have their own limitations (expensive, single gun which doesn't like immob result). It becomes an auto-include on the Dreadnought and bare Razorback because of raw efficiency. It's dirt cheap at 5 points and makes their effective weapons much more potent. In the Razorback's case it actually makes a Heavy Bolter weapon turret a very viable and dangerous gun whilst remaining cheap whilst on the Dreadnought, particularly with autocannons, it raises the ability of the unit to deal damage to tanks.
There are of course other options including the Stormraven and Land Raiders. It's cheap as chips on Land Raiders and makes all those Heavy Bolter, Assault Cannon and Hurricane Bolter options much more effective but unfortunately also turns Hurricane Bolters to S5, no more defensive status for you. For 5 points this is a pretty good option on even the Godhammer variant but the lack of defensive Hurricane Bolters needs to be weighed up on the Crusader variant. The Stormraven however pays a staggering 20 points for this upgrade but does have two weapon systems which initially benefit from this upgrade (heavy bolter and assault cannon). The Stormraven can also take Hurricane Bolters but once again this makes them lose defensive status. The increased cost of psybolt ammo makes it less worth it on Stormravens but a basic Raven with psybolt ammo does put out three S6 and four S7 shots on the move which isn't too shabby. If you add Hurricane bolters the Raven comes in at 255 points which is quite steep so I'd tend to avoid this option and either run Psybolt ammo/HB/AC or Hurricane/MM/LC or PC.
Psybolt Ammon on Infantry
The effects of Psybolt Ammo on infantry are easier to understand as it will only affect stormbolters as there are no heavy bolters, assault cannons, autocannons, etc. on infantry units capable of taking this upgrade. This means for any infantry unit psybolt ammo gives them S5 shooting at 24". Now S5 isn't exactly the greatest thing since sliced bread but it does vastly improve the amount of wounds the unit will generate against even your basic T4 model and adds some minor utility against armor (i.e. AV10). Importantly though, the combination of S5 stormbolters and psycannons is hell against high toughness targets such as Bikes or Monstrous Creatures. In the end S5 is great utility but isn't going to give the unit extensive anti-tank ability (psycannons cover that regardless) but rather extra ability to generate wounds on infantry models. Since the Grey Knight army as a whole generally doesn't have this issue with so many stormbolters, psybolt ammo isn't the most necessary of upgrades.
That being said, it is of course a useful upgrade and one I am particularly fond of in certain situations. Psybolt ammunition is 20 points per squad regardless of size. This makes it more effective on larger squads and less so on smaller squads. For this reason psybolt ammo should only be considered on larger squads where it becomes 2 points a model. Buying it on smaller squads where it is around 4 points a model is highly points inefficient so should really be avoided.' It's important to remember as well that models with Pyscannons aren't gaining any benefit from this upgrade so the effective cost per model is raised the more psycannons you have in the unit. For this reason, Purgation, Paladin and Purifier squads which have access to a lot more special weapons (four at squad sizes of 10) shouldn't really consider this upgrade as it is less cost efficient.
Conclusion
Psybolt Ammo is just an automatic on certain tanks thanks to the cheapness of the upgrade and the importance of having an extra pip of strength on particular weapons. There are quite a few tanks which can take this option which aren't auto-includes but there is quite a lot of utility and options there to really increase the firepower of a given tank. On infantry units it's less clear cut as it is more expensive. Even on full squads it isn't a necessity as the new strength doesn't 'unlock' utility such as good anti-tank. Some utility is provided to the unit but more importantly, the reliability of the unit's anti-infantry is improved and this is ultimately why you take this upgrade on large infantry squads.
