Fuller and Cockbain hurt Northants
James Fuller's best first-class figures and 99 from Ian Cockbain put Gloucestershire in a winning position on the second day of the LV=County Championship Division Two match with Northamptonshire at Bristol.
Fuller claimed 5-29 from 10.4 overs as the visitors were skittled for 100 - their lowest score of the season - having begun the day on 73 for seven.
That gave Gloucestershire a first-innings lead of 120 and Cockbain ensured they built on it, striking 15 fours and a six in facing 130 balls.
Will Gidman contributed 52 not out and brother Alex 40 as the hosts closed on 286 for six, 406 in front.
After 17 wickets fell on day one, bright sunshine suggested better fortunes for the batsmen, but there was no sign of it during the morning session.
Northants were able to add only 27 runs as David Willey fell to Anthony Ireland and Fuller cleaned up the tail by sending back Jack Brooks and Luke Evans to complete his first championship five-wicket haul.
The 22-year-old Cape Town-born seamer, who was brought up in New Zealand, can prove expensive at times but has the knack of producing wicket-taking deliveries.
When Gloucestershire lost two wickets for as many runs at the start of their second innings, a two-day finish looked possible.
Ed Cowan contrived to run out partner Benny Howell with a poor call for a single and then fell to a catch at third slip, driving at a wide one from Willey
Dan Housego helped Alex Gidman steady the ship with a stand of 64 before also falling to a slip catch off Andrew Hall for 24.
At 70 for four when Alex Gidman was lbw playing across the line to Evans, Gloucestershire's lead was only 190.
Cockbain and Hamish Marshall then began to take the game away from Northants with a stand of 98 that ended on the stroke of tea when Marshall fell to a sharp catch at point by Stephen Peters off Evans for 30.
Cockbain has struck a rich vein of form recently with three fifties and a hundred in his last seven championship innings.
The 25-year-old Merseysider looked set for three figures again until losing concentration and falling leg-before to Hall playing down the wrong line.
By then Gloucestershire had 246 on the board and led by 366. But it was a crestfallen Cockbain who made his way slowly back to the pavilion, having mastered a pitch few batsmen looked at home on.
Will Gidman piled on the agony for Northants with some meaty cover-drives as the lead approached 400 on a near cloudless afternoon. The left-hander reached his fifty off 94 balls to help put Gloucestershire in control.