Sniping implies shooting rats at long range. Using crystals that significantly reduce your weapon range does not fit well with the general concept of “shoot them at long range”. Here’s a table that lists what effect each type of crystal has on weapon range and cap useage.
I’m not saying you can’t use Gamma or X-ray at all, I am saying that you will need to have some other crystal that gives more weapon range to start shooting with, and then switch to Gamma or X-Ray or possibly even Multifrequency as the rats get closer (because they’re not going to sit still and let you pop them). Depending on what range you want to start shooting at, you will probably want to have Standard or Infrared crystals as your “opening act” and wait for the rats to get close enough for the higher dps (and shorter range) crystals to be effective.
You also need to ask yourself what distance will work for sniping. I do have a PVE sniping setup that works in L4 missions, but it’s not based on lasers as the main weapon. My setup can reach targets at a little over 110 km and still works decently a little under half that range, about 50 - 55 km. At less than 50 km, it depends on the size and speed f the target. For big slow battleships, I can keep going without having to change anything, but for smaller, faster rats, I may need to switch ammo types or use drones, or move my ship to open up some space and go back to sniping mode.
For a laser based sniping setup, the Nightmare gives the best options for maximum range. It can lock targets and shoot them at 120 km without any upgrades to sensors or range upgrades to the weapons, but you do need max skills for that, and a Nightmare is a bit pricey. A Blood Raider Bhaalgorn might work despite it’s bonuses to cap warfare (which is short range) and webbing (also short range but can be useful for dealing with small fast targets), but I haven’t looked closely at this ship before so I can’t be certain how well it would work as a sniper since several of it’s bonuses are for short range systems.
That leaves the Amarr Abaddon and Apocalypse as the other two main choices for a laser sniper (the Armageddon is drone bonused, if you want to snipe with a Geddon, use sentry drones not laser turrets). The Abaddon and Apoc both only have 4 mid slots so some careful choices are going to be needed on what mid slot modules you will fit. The Abaddon has better sensor range without any sensor upgrade, the Apoc has better weapon range and weapon tracking without any weapon upgrades. There is also a “navy” Apoc that has better overall stats, but is several times the price of a basic Apoc.
I might spend some time experimenting with a Bhaalgorn sniper setup on the test server, but it’s Christmas Eve and I’m about to leave town for a week, so I don’t expect to look at this idea until after the new year, unless someone else has tested the Bhaal in this way recently and decides to comment.