Ah yes, I welcome you to a Time Honored Corps of PvP'ing AR/Devs.
The Few, The Proud, The Incredibly Stubborn!
I've been known to be a formidable PvP'er in Virtue (or a dirty, cheap killstealing *******), but it's been a tough road. First off I'll say that Cpt Shwan is pretty much my only character I've ever played in my 4 years of CoH, so I've invested HEAVILY (quite a bunch of purple sets, a few PvP IO sets etc. etc.) Even still, trying a stand up knock around fight with most Villains is complete suicide, but I've always determined that to be for the arena anways.
AR/Dev makes for a damn fine squad leader role in PvP. Dark Master's strategy's is sound and mine is very similar, except I don't bother with +stealth because A) my squishyness is often overstated and B) If I draw out the enemy my backup will be there with me.
For Slotting, there's very different routes you can take. My Primary build works on +Dam and +Recharge so I can pump out as much damage as I can. My secondary build I'm working on right now is more along the lines of Malice's post, I'm slotting heavily for specialized ammunition, putting the chance for holds and immobs and all that jazz into my faster attacks like burst and slug.
Also getting the stuns and holds are good. I dropped beanbag for Tazer because I was finding I was only really using it when I'd have a melee fighter up in my grill. Later down the line in RV and Warburg the Cryo Ray can be pretty solid. Though high level your bread and butter is Surveillance. This attack is so great. for Soloing it drops the Res to your S/L damage making you do the damage you should be doing (before ED came about) and for a team it's perfect because it's a good marker to focus your teammates to a target (everyone knows and sound and sees the reticle on the guy) and it drops the defence and res of the target so he gets dropped quick.
Assault + Tactics are a must in my opinion. It adds to your Squad Leader role giving your teammates a buff, and it turns you in the designated stalker hunter (with the Targetting Drone and the +Per IO in it you pretty much at near max perception and the Assault gives you placate resistance) So you can snipe the stalker that about to assassin's strike your scrapper buddy and reveal them to your team for a quick beat down. Adding to the anti stalker arsenal caltrops are invaluable for the time you KNOW where that jerk is but his hide is too good, drop the caltrops on him and watch the fireworks.
Getting +Range in your Snipe and your Web Grenade is a good move. You'll never catch anyone if you have fly, but you don't need to because no matter how super you are, you'll never outrun a bullet. With the cheap jetpack proliferation going around, the skies are alot more unfriendly than in the past (which is BS and I'm waiting for the red names to give power pool fly an ACTUAL improvement to make it worthwhile to have) so you gotta keep moving and have that web grenade and hover ready. Your Hover will usually keep you in the skies and your web grenade will ground them, but you wanna make sure your web grenade's reach is longer than your opponent's.
Finally, I would say this. Don't be afraid of using Inspirations. Your already at an almost insurmountable disadvantage so go ahead and pop some reds to make up for the fact that by Warburg, all your opponents have AT LEAST +10% S/L resistance. PvP Zones are a Team Event so with your powers and skillset, get used to starting groups and giving them commands, maybe make some binds or something, it's always the most organized team that wins in PvP zones.
That's all I have. Just remember, Your the Jack*ss running around with the rifle in a City of Heroes and Villains, so keep your wits about and take any advantage you can get!