The thought just hit me: what happens to the threads on the barrel when an AK-74 front sight base is attached?
nothing. your norinco has a fsb journal diameter of .594"
the bulgarian fsb has a .575" hole in it. iirc, you will have to drill new cross pin hole locations in your bbl. and either open up the fsb press fit hole or turn your bbl. down a bit in order to achieve a fit.
All Soviet AK's have had a threaded barrel, even the early ones with no muzzle attachments. Did they drop the barrel threading on the AK-74, since the FSB itself is threaded?
yes. the akm (1959-1973) was the last model to have a threaded bbl..
Did they leave the threads on as a vestigial arrangement?
no.
Or do the muzzle threads somehow work with the new FSB?
no. your existing threads will be covered up by the threaded projection on the bulgarian fsb.
It looks like the threaded barrel on mine would poke into the blast chamber on the brake.
no. your old threads/muzzle crown will stop about even with the end of the threaded projection on the bulgy fsb....give or take a 1/16".
So do '74's have the barrel shortened by this much?
the bbls. remained the same length. the ak-74 style fsb is longer, with an integral threaded projection on it.