.30 cal Browning in AVG Hawk 81 (P-40B, Flying Tigers) cooling jacket question

[MrSmoothie]

Can anybody confirm the diameter of the early type cooling jacket (slots instead of holes) on the .30 cal Brownings mounted in the wings of the AVG's Hawk 81's? I found the attached drawing -- when scaled for the 1/8th scale model I'm working on, the resulting 0.25" diameter barrels look large as compared to photos. This made me wonder if aircraft MG's may have had a different cooling jacket of smaller diameter. It might just be an optical illusion.

 

[MiTasol]

There are several gun websites offering good quality blueprints for various guns like www.john-tom.com so a search for .30 browning machine gun blueprints may find what you need but this one may be all you need Browning M 1919 A 4 Machine Gun. 30 Caliber, Complete Set Of Ordnance Blueprints : Free Download, Borrow, and Streaming : Internet Archive tho they are dated 1927 and only cover the round cooling holes from memory.