Missing Febian Brandy with a thigh strain, Mark Stimson reverted to a 4-5-1 formation with Curtis Weston playing off the shoulder of Simeon Jackson.
The first half was a cagey affair with both sides looking to control the midfield, Carlisle's best opening saw Pericard head over from close range while for the hosts, Barcham failed to connect with Jackson's square ball at the opposite end.
On 20 minutes Andy Barcham created the best opening of the half with a strong run down the left before cutting into the box but Collin reacted well to block his shot.
Gillingham arguably shaded the possession but all too often the final ball wasn't good enough to deliver the goal their efforts deserved.
Three minutes from the break Simeon Jackson's incisive pass allowed Curtis Weston to race through on goal, he appeared to be clipped in the area but referee Singh waved away the penalty appeals and booked Simeon Jackson for protesting to the linesman.
On the stroke of half time Simon Royce raced out to spare Chris Palmer's blushes after the full-back had under-hit his back-pass as both sides went into the break all square.
Seconds after the restart Gillingham should have had the lead as Barcham made inroads down the left before cutting back for Jackson who sliced agonisingly wide at the near post.
The Gills had the bit between their teeth and went close again soon after as Weston teed up Jackson to thunder in a shot from the right that keeper Collin pushed over the bar.
The Cumbrians response saw Matty Robson fire an inviting ball across the face of goal but Richard Keogh could not find the finish at the far post.
On 65 minutes Robson crossed for Pericard to head goalwards again but his effort was placed at a comfortable height for Royce to gather.
In the 73 minute Weston played in Jackson on the right of goal, the striker took a touch but mis-fired horribly, shooting high into the Rainham End.
Seven minutes from time Jackson's flick found McCammon in the area, the big striker shot on the turn only to see his effort deflected wide off the backside of Chris Palmer.
Then in the 86th minute Simon Royce kept his side in the game with a stunning save to push Ian Harte's free-kick around the top right corner.
Two minutes from time McCammon sent Jackson goalside with a flick-on, Jackson fired his shot on target but Collin was there to deny the Gills leading scorer. As he was again moments later to block Chris Palmer's drive from distance.
Jackson was on target once more in time added on with a low strike from the centre of goal which was comfortably held by the Carlisle custodian
Attendance: 6214 (visitors 242)
Gillingham: Simon Royce, Barry Fuller, Josh Gowling, Matt Fry, Chris Palmer, Mark Bentley (Mark McCammon 75), Curtis Weston, Kevin Maher (Dennis Oli 75), Stuart Lewis, Andy Barcham, Simeon Jackson
Subs not used: Alan Julian, Rashid Yussuff, Luke Rooney, Jack Payne, John Nutter.
Carlisle United: Adam Collin, Evan Horwood, Danny Livesey (Peter Murphy 61), Graham Kavanagh (Scott Dobie 68), Matty Robson, Tom Taiwo, Ian Harte, Vincent Pericard, Richard Keogh, Kevan Hurst, Adam
Subs not used: Joe Anyinsah, Conor Tinnion, Michael Burns, Tony Kane, Lenny Pidgeley.