Rob Allen Aluminium barrels are made from aircraft grade aluminium and hard anodized to increase it’s resistance against corrosion and wear.
The internal diameter is in the range of 26.2mm, outside diameter at 29.2mm with a wall thickness of 1.5mm. These dimension will vary a little.
These barrels are pre-fitted with plugs for the purpose of buoyancy but not drilled. To clear the handle spigot the plug has been inserted at 65mm whilst the other end has a clearance of 35mm for your muzzle.