Hello,

I just pulled apart two of my No.5s, and here is what I came up with

(all measurements taken from the rear of the handguard)

overall length=225.42mm

length to the barrel band groove=201.61mm

barrel band groove=11.11mm

remainder, from front of groove cut to front of handguard=12.7mm

Handguard manufacturers were both Fazakerly (F) and BSA (M47A).

Best of luck with the project.