Record would not be so grand
The Mets have allowed 10 grand slam home runs this season. That is two short of the National league record, held by the Montreal Expos (now Washington Nationals). The major league record of 14 was set by the Detroit Tigers in 1996.
By the way, the Mets have not hit any grand slams this season.

Mets trade Jeff McNeil to A's for minor-league pitcher
3m read
New Met Polanco expects 'good amount' of time at first base
3m read

Polanco on playing first, joining the Mets
Report: Mets, Yankees have to pay millions in luxury tax
2m read

Rieber: Mets may be forced to move young pitchers to make big splash
4m read