Here is something I did a year or so ago but I thought it was worth resurecting for the barrel info.
I am informed it may be a 6.01mm barrel i have also done this on my MP001 Chinese sniper rifle.
Free speech is expensive these days!
Can you explain a bit more Oddball, are you saying 6mm i/d aly tubing is avaialble from from B&Q but needs ot be modded ot fit the hop unit ?
I will correct Oddball, last time I was in B&Q it was
Well the length of the pipe is 1m so you can make about 4 MP40 barrels for
Free speech is expensive these days!
Thought I'd give this a go, could only get the 8mm tube and when I got it home the internal diameter is too small to take a 6mm BB 
The trick is to take a internal micromiter & some bbs with you, its no good for the mp40 barrel though as you have to butcher the hop unit & you may as well mod the hop too & fit a TM compatible barrel, ideal for the cheap sniper rifles UTG etc, the Mp-001 has a good barrel to start with & makes little diffrence, where as some are very poor, UTG M234 being the worst I have ever seen, somwhere in the region of 6.10mm,
Ste.D
Also, you have to watch out which ones you get too. Well stocked B&Qs offer two types of ally' tube. One is a kinda polished finish raw ally type , probably extruded, this is the good stuff to make the barrels out of. The other is a clear annodised version, which is a 'rolled' tube with an obvious internal seam mark. This stuff is good for making ammo feed tubes for custom boxmags, etc..
And HomeBase (the stores which stock it, at least) is cheaper than B&Q.
A Proud Member Of 'Team Spleen!' who play mainly at Gunman Airsoft, Tuddenham, Suffolk.
As Ste did heat up a pin and push it through a BB and take that with you as some of the 8mm OD pipe have different internal sizes.
This does not mean that they change in size over a length at least I have not found this.
Don
Free speech is expensive these days!
Pete_59, I have 1/2 a length of that tube if u want it, I can bring it to Churchills for you, its 23" long,
Ste.D
