I'm not sure where to interject this comment at such a late stage in the thread, but here goes: Some of the confusion *might* be in discussing field Whitworths versus the heavy siege/garrison Whitworths. The siege caliber Whitworths had some bursting problems--like the "Lady Polk" that burst after the Battle of Belmont. The Feds didn't have much luck with the 5" pieces they put in service as siege pieces.
The field Whitworths tended to become disabled at times, but lack of ammunition appears to have been their greatest weakness in several engagements.
By the way, if anyone has found some specs for the field carriage (English or CSA), please post or provide a link. I've been searching for information on this.