First thing to note, kill times in Halo 4 are about as fast as Halo 3 vanilla/ Reach’s zero bloom settings. I know a lot of people were hoping for faster, what with base player movement speed being increased to Halo 3 levels and Sprint being a universal ability. But Halo 4 has stopping power so the effects of sprint should hopefully be irrelevant in a gun fight.
The most likely reason for these slightly slower kill times, the way I see it, is probably an attempt by 343 to balance CQC niche automatic primary weapons with utility weapons without having to buff the Automatics too much.
Anyway…So let’s start with the BR verses the Carbine. The Carbine in Halo 4 appears to share the same stats as the Halo 3 Carbine but conversely the BR has been nerfed slightly. In Halo 3’s vanilla matchmaking I personally found the BR to be a superior weapon to the Carbine. The kill times seem to back up this theory. MLG attempted to fix this by playing at 110% damage making the Carbine a 7 shot kill as opposed to 8, giving the Carbine a faster kill time than the BR. The BR became an 11 bullet kill making 4 shot kills more consistent and still had its perks, like being an easy clean up weapon and having an easy 5 shot kill. Overall I think 110% damage worked pretty well.
343 seem to have gone the opposite way. Instead of buffing the Carbine they have nerfed the BR. They have increased the fire rate but reduced the damage per bullet and the overall kill time. It only takes 1 more bullet to kill mind you. Making the weapon a 13 bullet kill, meaning you can miss 2 bullets and still get a 5 burst kill. Also I might be mistaken but it appears they have halved the duration of the burst as well which will tighten up the bullet spread. On face value this appears balanced to me.
Now let’s look at the DMR. It is a single shot weapon just like the Carbine but with some key differences. It is a 5 shot kill but has a slower fire rate, it has a significantly faster kill time, it has a 3 times zoom giving it a larger range of effectiveness, it has a more lenient clip size allowing for 2 kills with 4 shots spare but on the other hand has less aim assist and less bullet magnetism. It also has Bloom for some reason 
but it only seems to effect cross mapping unlike Reach. The fire rate seems to have also been increased when compared to Reach’s DMR giving it the same kill time as the Halo 3 MLG BR.
I’m struggling to find down sides of this weapon. Right… When compared to the BR it is easier to drop a shot in a strafing duel because it is either a hit or a miss, the burst firing of the Halo 4 BR kind of acts as a safety net in its current form. When compared to the Carbine dropping a shot is more punishing because of the slower fire rate and it is easier to drop a shot in theory due to the reduced player assists.
But all this still means a DMR wielder still has the advantage in a straight head to head, both BR and Carbine wielders are dependent on the DMR user missing a shot to win which may or may not happen depending on skill levels. From my experience weapons with slower fire rates are easier to shoot consistently with simply because you have more time to correct your aim between shots and there is less opportunity to miss shots simply because you are firing less shots in order to kill. Also even with weapons that are primarily long range weapons, it doesn’t mean it becomes any less effective the shorter the range, aiming is in fact easier because the target is bigger. If you can 5 shot someone at long range, you can 5 shot someone short/ medium range. Saying the primary means of balance is aim assists is basically admitting the weapons will become imbalance at higher skill levels and it is more worthwhile investing time getting better with the more powerful weapon because the rewards are greater. But I mean, I do prefer the weapon with a superior kill time to be a skill weapon. Alas.
Now… The Light Rifle. The Wild Card. Dual firing modes, fastest kill time of any weapon, 4 shot kill, but only when zoomed in. hmmm. This weapon for me at least is the most intriguing. It has the potential to kill 3 people in 1 clip when zoomed in and the maths seem to suggest that you only need to land 1 zoomed in shot, followed up by 3 bursts to achieve a 4 shot kill, although this would still mean a 1.4sec kill time since it would require all 9 bolts of the 3 bursts to kill. Statistically the Light Rifle when unscoped has the same specs as the BR, 13 bolt kill, 5 burst, same fire rate, but has less player assists, it has a 3 times scope and when zoomed in it has a significantly slower fire rate than the DRM but it isn’t enough to stop it from having the fastest kill time of any primary utility weapon and you don’t get knocked out of scope when shot as it stand making the Light Rifle even more powerful.
Lastly the Magnum . Despite now being a 6 shot it actually, if spammed, has the fastest kill time of any utility weapon. Which surprised me. But on the down side, it is least accurate by far and has the most punishing clip size- 8. The magnum is relevant because it is effectively the utility weapon of Automatic wielders not using Fire Power.
Weapon balance may have been tweaked since the Euro Gamer build so it might be different in the final game but as it stands do you think the sandbox is balanced?