Nick,
During the Cambodia Incursion in 1970 we had CH-47A model Chinooks with Lycoming T-55-L7C engines......SOP external loads were limited to 8,000 pounds for us.....6,500 pounds for 1st AirCav Chinooks.
We burned off a thousand pounds of fuel on the first 8,000 pound load then started with double loads. One count of 105mm Pro Joes showed us at 16,800 pounds. There were times we argued about how to clear the three foot high barbed wire fence around the resupply area.
It was possible to do a running takeoff with a 3/4 ton weapons carrier inside and one on the sling....the trick was to have a guy steer the external vehicle until we got ETL then he jumped off.
The major trick was landing....invaribly the front wheels turned to one side or the other during flight and timing was of the essence to allow the vehicle to touch down simultaneously with the release of the cargo hook. Watching the runaway wagon with a posse chasing it was good fun however.