I've done some research on all the weapon weights for AJS37. Between the 75 and 75T, the 75T is closest to the real life weight, if you include the mounting rail.
All weight below are with the rail included, and as you can see, most things are too light if anything. The 75 has it's weight without the rail, otherwise correct. Most of these are from "SFI AJS37, del 2" kap. 4, p.34, or page 190.
[TABLE]Weapon Real DCS Diff
SB 609 609 0
LB 285 220 −65
RA 387 372 −15
75 258 210 −48
75T 343 354 11
04 661 661 0
15 605 610 5
05 341 341 0
BK 605 605 0
AK 364 276 −88
74 123 90 −33
24J 119 90 −29
KA 348 348 0
KB 316 296 −20
XT 195 195 0
[/TABLE]