I'll try to keep it short and sweet. Trying to keep the flavor and intent of AR, but making it more... better? The theme of AR is ridding baddies with bullets and/or setting them on fire. Also in some instances I'm asking for KB to KD. I know there's a IO for that but IMO we shouldn't have to dedicate a slot to reduce KB, people that love the KB (not many) can dedicate a slot to adding it back. Keeping that in mind...
Burst - Make this a narrow cone. Everything else stays the same. Concept: spray and pray.
Slug - Give this ability a small -res to s/l effect. Concept: the Slug can damage/shatter armored plating.
Buckshot - increase the range of this attack so you can hit enemies deeper in the pack, or more spread out enemies. Change KB to KD. Not much conceptual stuff here, I just think the power would be more useful if it could spread more. And it fits the theme.
M30 Grenade - KB to KD. Animation option - add an option to give this power the hand grenade animation. Not all gun options make sense with an underbarrel launcher. Change the smashing damage aspect to fire damage. Concept: It is an explosive after all.
Beanbag - change to Flashbang. Animation choice, shoot from gun or throw grenade by hand. Change power to a targeted AOE stun and to-hit debuff. Adjust stun mag and duration to be in line with the power type, etc. Concept: this power is in line with a munitions/soldier type and it actually makes the power useful.
Sniper Rifle: Add "Headshot" mechanic. Power will crit if the user has > 22% tohit buff. Concept: UT99 rules.
Flamethrower - Speed up the cast time and the power deals 75% of it's damage as an upfront burst, the rest as Dot. No concept here, just a buff to usability.
Ignite - Change to Incendiary Grenade. Animation choice, shoot from gun or toss grenade animation. Increase range. Effect: Exactly the same.
Full Auto - Increase target cap to 16 and add a high stun effect whose duration is equal to the animation time of the attack. This will keep you a little safer during its notoriously long animation time. Concept: Think Arnold mowing down trees in Predator. The stun effect simulates the reaction of being Full Auto'd "OMG I'm being Full Auto'd!" no time to shoot back till the hail of bullets is over. Other tier 9 nukes have secondary effects so its not unprecedented.
That's all I got.