I did a .223 saiga a few years back and used the pipe method...I used 3/4" pipe. (wall thickness unknown)
I had also used the screw in method, so I could test fit for function(feeding) and then remove to "tweak" as nessesary. It took me several tries to fabricate one that functioned nearly perfect.
I also found that the dual feedramps worked better on the .223 than the 7.62x39.
I am going to do a 5.45 conversion next, but plan on using a feedramp from a donor 74 trunnion I bought for $20.