For this review, I'm just going to compare them to each other in terms of Damage, ROF, etc.
Rifles For Review:
M4RA Battle Rifle: Scout spec
M42A: Typical Sniper Spec
XM42B AT: When you pick sniper spec, send an A-help in-game for this AT rifle. You may get lucky and get it if admins are feeling kind (like they did for me).
Damage Per Shot:
M4RA: Decent damage per shot, about 1/4 - 1/3 of xeno health per shot.
M42A: Decent damage per shot, about ... eh ... 1/2 of common T2 xeno of mature or elder per shot.
XM42B AT: Does an INSANE amount of damage per shot, almost 3/4 to 4/5 of xeno health, making it almost the PERFECT finisher OR deterrent for ANY xeno wanting to fuck with your FOB.
Rate Of Fire:
M4RA: Same ROF, if not higher than that of your standard M41A ... and that's saying something.
M42A: Pretty decent for a sniper rifle, given it's capabilities of damage. You can actually pump out shots relatively quickly.
XM42B AT: ... I'm not gonna lie this is one of the aspects where the AT rifle falls short. You may as well pull out your pistol and run after the xeno rather than wait to take another shot. It's virtually a super-slow bolt-action-rifle.
Ammo Capacity and Variety:
M4RA: Has a ... less than optimal capacity of 15 rounds per mag, particularly since that goes down FAST. But with the capability of having m41a ammo loaded into it, I'm willing to look past that. It also has one type of ammo that is absolutely insane besides incendiary rounds, impact rounds, which are literally bullets that deal damage, AND STUN THE TARGET. A literal NIGHTMARE for xenos who are caught out in the open.
M42A: Has a nice ammo capacity of 15 rounds per mag, with multiple types of ammo available including incendiary.
XM42B AT: This is also where the AT rifle falls a little short. It only has 5 rounds per magazine due to the sheer SIZE of the fucking bullet (10x99)! It also fails to deliver in any other type of round besides the normal one. You also only start with 3 extra mags ... which means you can only take 20 shots ... yikes.
Attachments:
M4RA: Arguably the most 'attachable' out of all the spec, and even the smartgun weapons systems, as you can fit almost any grip and/or barrel to it with the exception of course being the built-in scope and stock on the rifle.
M42A: Can only fit Bi-pod
XM42B AT: Can only fit Bi-pod like it's M42A counter-part.
IFF Features:
M4RA: No IFF features ... kind of a bad downside.
M42A: Typical IFF Features.
XM42B AT: IFF Features with a SUPER ANNOYING one in which it won't allow you to fire it unless you're targeting something over 5-6 tiles away ... kiiind of annoying.
The following ratings are given out of 10:
Difficulty and Handling (In My Opinion):
M4RA: 6/10, A little above your average M41A or M37 Shotgun to master, but a GREAT starter for people who haven't been spec.
M42A: 8/10, Very difficult to master, as your shots don't exactly instantly-crit xenos who have little to no damage, and the closer the target is, the more likely you'll miss. You also have to watch your flanks ALL THE FRIGGIN' TIME.
XM42B AT: 10/10, One of the most difficult weapons to master in the game in my opinion. I have had more trouble with this ... fucking gun ... that I have negotiating with my MOTHER on premis' of dis-respect. Not only do you have to consider your low ammo count, but you can't just take another shot in 2-3 seconds like the M42A if you miss. You have to wait almost 10 seconds ... TEN FUCKING SECONDS!!! Not only that, but if the xenos learn you have this gun ... hoooo boy, you are going to get T A R G E T T E D like no tomorrow because this sucker HURTS.
Now this doesn't mean this weapon is absolutely terrible, it doesn't mean it's complete shit and isn't worth it, it's just REALLY ... REALLY hard to get it right.
Damage:
M4RA: 6/10, You deal some decent damage, but only about 30-50% more than your typical M41A rifle
M42A: 7/10, You pack a punch, but don't let that go to your head. A xeno can take 2 of these and still not go down.
XM42B AT: 9/10, ... the only weapon that hits harder than this mother fucker, is a SADAR loaded with an AP rocket ... I shit you not, you can 1/2 the health of a QUEEN with this thing, it's crazy.
Mobility & Offensive Play:
M4RA: 8/10, Not only can you deal good damage, you are almost as fast when wielding it as you are when you're not. You can RUN with this weapon in your hands. It's super-light, and has a nice scope to pick off xenos running away that comes in handy with your scout sight as well. The only reason why it's not a 9/10 is because there's no IF- GOD DAMMIT WHY DID YOU WALK IN FRONT OF MY INCENDIARY BULLETS PFC!!!
M42A: 4/10, Eh ... for a sniper rifle it's actually not that bad in terms of mobility, just watch your back or a lurker is gonna come along and meme your ass to kingdom come.
XM42B AT: 4/10, ... jesus christ this weapon IS SO DAMN HEAVY!!! You may as well be carrying a fucking SADAR, and as such you should NEVER EVER wield it unless you're actively looking for a target or defending a barricaded position. Not only that, but offensively, it's so bad because you can fire ONE SHOT in around every 10 seconds ... and that is BAAAAAD. Albeit one good thing about it offensively is it GUARANTEES a kill if you shoot a critted xeno with it while it's friend is dragging it away. Hell, you may even crit the one dragging it away, SCORE ... if your PFC's push. The reason it's not a 3/10 is because it has IFF Features.
Defensive Play & Traps:
M4RA: 4/10, You're better off with an M41A Rifle, because the way xenos win is not by slashing you until you're in crit, it's by getting YOU to shoot your FRIENDS in the back until they crit, then pounce and kill you and your friend. Albeit the spec loadout enables you to cloak, which can be REALLY HANDY defensively, which is why it's not a 3/10.
M42A: 7/10, Albeit it won't crit young T1's in one shot like the fucking AT rifle or stun them like the M4RA, it'll sure as hell give xenos something to think about as they sit for almost a full minute to recover from just 2 of your shots.
XM42B AT: 9/10, If I was a xeno assaulting an FOB, the LAST fucking thing I'd want to see on the marine arsenal is this fucking gun. If you get down to 1/2 health as a xeno and start running from an FOB, or you pounce on a marine with a shotgun and get blasted by a round from one of these suckers ... it's virtually game-over for you if you have an XM42B looking at you. The ONLY reason this isn't a 10/10 is because ... dear god THE RATE OF FIRE IS soooo ... friggin' ... BAAAAAD ... AHHHHHHHHHHH I ALMOST KILLED THE ANCIENT T3 ... FUUUUUUUU-
Recommendations:
For new people who have NO IDEA what a spec is/supposed to do, go scout spec, you'll actually enjoy it. You also get the benefit of being able to call down the fairy god-mother of CAS and lay down some hell on xenos. Just ... don't get too cocky, and use your cloak to escape.
For people who want to avoid FF'ing their allies, but don't want to be too worried about watching their backs, the normal sniper is for you. Just make sure you either watch your back, or stay in a fortified area.
For people who are; 1. VERY good at watching their backs / situational awareness; 2. Is experienced in CM13, and; 3. Want to be a SADAR with IFF and a scope . . . then the XM42B AT is for you.