With an assault rifle you lose like 90% of your encounters.
Who thought this was a good idea when this game was in development.
Who? Bungie.
Bungie has been adamant in starting you with an easy to use but weak gun. It was only until the community complained that they added and weighted BR starts heavier. It was brutal in Halo 3 where every AR fight was running at each other and trading melee kills. Extra brutal when you played against a good team and that team got control of the BR and power weapons. Have fun getting wrecked. Bungie, at the very least, introduced a SERVICEABLE pistol in Halo Reach. If you're on AR starts switch to pistol immediatley. 5 shot kill with the headshot. Bloom is a bitch on the thing though.
Also, I really need some tips about controlling DMR bloom. I am absolute buttcheeks when it comes to DMR slayer and it seems like everyone else I play against can 3-4 shot me no problem. I've heard you need to pace your shots, but pacing them in a 1v1 just means I die first because someone else is shooting just slightly faster and landing better hits.
Like others have said... welcome to Reach. It can be a crap shoot. The only thing you can do is push the odds in your favor. Are you down a shot or two? Spam because you might win out. Are you up a shot or two? Hold for the final shot to get the headshot. My general strategy is to spam the first 3-4 shots and wait for the headshot but it all depends on the situation. You gotta learn when to spam, when to pace, and just know that all that does it push the odds in one direction or another.
what's this "bloom is reduced and bleed through is enabled" stuff I see when loading into matches?
It's their really dumb way of explaining TU settings. In short - it means the reticle blooms less and melee damage can go through shields and health. Ie if the persons shields are up but weak enough, a melee will kill them.
A history lesson: Reach launched with a much higher bloom rate. Meaning the pistol, DMR, and needle rifle reticles expanded about 15% more with each shot. If you thought pacing your shots was excruciatingly slow in TU settings it was BRUTAL in vanilla settings. If you want a taste of that, play Invasion.
The way bungie handled melee damage and shields was also a big departure from Halo 1-3. In those games you can weaken the shield with some shots, melee, and the melee damage would break through the shields and get at your health and kill you. That is what bleed through is. When Reach launched they decided that melees do not get bleed through. Meaning if you put 13 AR bullets in someone and they have a SLIVER of shield left, your melee will not kill them. It will only strip their shield. This led to very frustating moments where you got the drop on someone and put more shots on them, but if they got within melee range and landed the melee you were now on even ground. To make matters worse, with the inclusion of sprint, it was a VERY viable strategy to just rush your enemy and land the melee.