It doesn't say anything about the width of the rear bag as long as you follow those rules...
From DCRA rules...
FTR – An FTR Class rifle is limited to .223 Remington or .308 Winchester caliber
chambers or their commercial metrification equivalents. Chamber dimensions must
conform to SAAMI or CIP dimensions. Ammunition maybe commercially made or hand
loaded as defined elsewhere in these rules. There is no restriction on bullet weight. The
FTR rifle class is limited to the use of an attached bipod and or sling as front supports,
optionally together with a rear bag, none of which provide a positive mechanical means
of returning the rifle to its precise point of aim for the next shot.. The overall weight
must not exceed 8.25 kg including all its attachments (such as, but m=not limited to, its
sights and bipod, if any)
From DCRA rules...
FTR – An FTR Class rifle is limited to .223 Remington or .308 Winchester caliber
chambers or their commercial metrification equivalents. Chamber dimensions must
conform to SAAMI or CIP dimensions. Ammunition maybe commercially made or hand
loaded as defined elsewhere in these rules. There is no restriction on bullet weight. The
FTR rifle class is limited to the use of an attached bipod and or sling as front supports,
optionally together with a rear bag, none of which provide a positive mechanical means
of returning the rifle to its precise point of aim for the next shot.. The overall weight
must not exceed 8.25 kg including all its attachments (such as, but m=not limited to, its
sights and bipod, if any)