Just get a Mk2 barrel turned down to be a Mk3 barrel
I don't think it's that easy. One would have to cut down the barrel, re-notch for the FH, and add metal to get the fat space mid-way.
That's assuming he already has the Mk3/4/5 front end (FH/ sight) because the sights are different.
A Mk 2 will fit fine; if he wants a shorter barrel, then the work can be done to make it look more Mk 3, and to use the Mk 3/4/5 parts. Seems like a lot of work though, when there are barrels out there (somewhere).
My suggestion: use a Mk 2 until you find a Mk 3/4/5 and just keep looking.
that is not correct. the fat space midway as you put it is the original diameter of th Mk2 barrel. that area is not turned down. the job requires shortening the barrel and fitting the flash hider and turning down the barrel. Its really a basic job to take a Mk2 barrel and turn it into a Mk3 or Mk4 barrelI don't think it's that easy. One would have to cut down the barrel, re-notch for the FH, and add metal to get the fat space mid-way.
That's assuming he already has the Mk3/4/5 front end (FH/ sight) because the sights are different.
A Mk 2 will fit fine; if he wants a shorter barrel, then the work can be done to make it look more Mk 3, and to use the Mk 3/4/5 parts. Seems like a lot of work though, when there are barrels out there (somewhere).
My suggestion: use a Mk 2 until you find a Mk 3/4/5 and just keep looking.