Irregulars (IR) are infantry who adopt a dispersed formation but remain standing, as opposed to the crouching of light infantry doctrine.
Ranged infantry include light infantry (LI) and the elite skirmishers (ES) that we all know and hate/love.
I don't typically obsess over statistics or prices, and as such I generally use LI over IR. But few people use either of those unit types because of their perceived weakness when compared to Line infantry (Line) and ES. This comparison of LI to other units in a head on fight is short sighted, simply because LI and IR infantry are not really supposed to be fighting their foes head on.
Instead of sticking LI or IR inf right in front of your line, as is often done with ES, put them on your semi-distant flanks in such a manner that they are not part of your line but can be supported by your cavalry if need be.
This way, they can plink away at the enemy flanks with relative impunity. This positioning is a superior prospect than having them in front of your Line as ineffective 'meat shields', as many of the rounds that fail to hit your LI will go on to hit your Line.
If the enemy sends cav after your flanking LI or IR, simply use your supporting cav (Light Dragoons do a great job for this) to hold the enemy in place while your flanking LI/IR plus any other units focus fire to destroy the enemy units. If he sends infantry, then pull back your flanking units so that he is either chasing one of them away from the fight (while getting shot by the other) or until your flanking unit(s) reach a point where they can potentially out shoot the enemy.
This leads me to my final point about LI and IR infantry. If they are in a position to get shot at you must use the terrain to minimize the damage they take. Forests, stone walls, bluffs and good micro, even those wooden fences will stop some of the enemy bullets from hitting your men, which will give them the advantage they need to out shoot (or at least render combat ineffective) the tenacious (or forgotten) enemy unit. If he charges you, simply use LI/IR's superior stamina and speed to out run the enemy.
This leads up to ES, and they should be treated similarly to LI and IR. However, Instead of starting out on your flanks, they should be placed along the enemy's advance so as to inflict heavy(ish) casualties on him. When your forces finally do engage, bring your ES off to the flanks and avoid leaving them just in front of your line as this will also lead to the 2 kills for '1' bullet scenario.
A few final pointers about these special infantry units:
- Always, always, always support them with cavalry. If you fail to do this they will be slaughtered by the first horse that so much as looks at them, even if you have a unit of Line there to 'support' them.
- Stakes should only be used to stop/discourage charges or slow down combat on a weak flank, as they stop bullets going both ways. Thus you should consider whose advantage it is to have a slow fire fight.