Well you can try this:
S 6 +2-2+1 = 7
P 6 -2+1 = 5
E 6 +2+1 = 9
C 1 -2 = 1
I 6
A 10 -1+1 = 10
L 6
Small Frame, Good Natured.
Buffout/Nuka/Jet/Psycho/Cigs
Lv3 Stonewall/Toughness
Lv6 More Critical
Lv9 More Critical
Lv12 Lifegiver
Lv15 Lifegiver/More Critical
Lv18 BRoF/More Critical/Better Critical
Lv21 Toughness/Stonewall/More Critical
12 AP
Recovery: 2.4 APs per second.
x2 bursts instantly, then 3rd burst in 3 seconds, 4th burst in 2 seconds, etc. 3 seconds, 2 seconds.
I'm not sure about dmg mults in torso, but if it unchanged from original fallout, then with better critical perk you'll have 19% to do x3 damage and more often x2 damage, rare x1.5 damage, without perk it'll be almost 50/50 x1.5 damage and x2 damage, but x2 damage a bit more often. With 9 EN you'll have 90% resistance against knock downs and 40% against knock outs with Stonewall perk. If you don't need Better Criticals perk, then you can sacrifice some PE. Tag of couse BG/FA/Doc.
Also:
S 3 +2-2+1 = 4
P 7/6 +1-2 = 6/5
E 8/6 +2+1 = 10/9
C 1 -2 = 1
I 6
A 10 -1+1 = 10
L 6/9
Small Frame
One Hander
Same drugs
Lv3 Toughness
Lv6 More Critical
Lv9 More Critical
Lv12 Lifegiver
Lv15 Lifegiver/More Critical
Lv18 BRoF/More Critical/Better Critical
Lv21 Toughness/More Critical
4 AP per burst with p90, easy leveling without drugs 3 ST is enough for 10mm pistol on mutated moles.
3 bursts instantly, then reload on the next second, then burst every 2 seconds.
Actually my main isn't burster, but.. well it is, I'm a sniper who accidentally have x2 BRD. I have only 15% critical chance, but it's enough to make my enemy worry if I'm too close with p90, than when I'm far away with sniper rifle. x2 BRD and Better critical perk will give you simply... huge number of damage when you crit someone, my record is around 560 damage to BA without bypass, usually it's 260-280, again to BA, don't know about toughness perks of my victim, because it wasn't time to ask about it. Also I have no BRoF and only 6 AG, because I'm again sniper and almost never burst someone from not point blank, because if I have opportunity to shoot from more than 1 hex I doing it with sniper rifle.
So if you're going to point blank shots only, then take 6 AG, 5 IN. I have only x1 More Critical and 10 LK giving me 15%, it's enough for me as for aimed shots in the eyes, and as bursting in point blank.
Universal build of sniper/burster isn't that bad really, because you can always hide from BGer outside on the street waiting him with sniper rifle, and sneak by running behind walls to sniper or someone, who was in wrong place in wrong time, with p90 to have advantage over both classes. And it's simple sniper build who uses x2 BRD instead of x2 More Criticals, yes, there's 10% difference in critical chances and it mostly seen for bursting than in aimed shooting because of 10 LK, but anyway x2 BRD + critical burst isn't that bad... 15% and 21% has not much difference, and 15% and 25% but without x2 BRD... again everything depending on your real life luck, but BRD makes it a but less dependant. Also again, if you're going for point blank bursts, then you don't need so much APs, because if your victim isn't dead after your 1st burst, it means you better try to run away behind wall from where you just jumped until his 10 friends wake up and kill you, 6 AG is enough, no BRoF, 10 LK, 5 ST and use assault rifle for casual playing, and P90+Sniper rifle for PvP.
Or just make 1st build at this post and always make bursts... but anyway I think it's better to make aimed shot at long distance and burst in point blank ^_^ Yes, you can have a friend who will play other role, then it's your choice which role to take, if not, then make sniper with x2 BRD instead of x2 More crit and play both roles when it mostly need.