to get the carrier tighter at lock up simply leave more rail when you build your receiver.
mine was done on a tapco flat . my custom jig is a few thousands narrower than standard. so I end up with a little extra upper rail when its folded over. this also gets the trigger pin holes up slightly off the bottom of the receiver.
I like to leave things standard except for the last 1/2" just before the carrier hits the trunion. I fit the rails in the last half inch tighter so there is not so much side to side clearance . I figure let it be as free as possably for 95% of the travel an then the last 5% get almost tight but not tot he point were it will affect cycling. if you try this with the entire reciver it will stop running when it gets dry an dirty.
If your using a prebuilt reciver or your bent blank that doesn't need trimming you can tig a little extra to the rails. . back it with a copper plate when welding.
I cant say how much it helps as I have not done back to back tests but I can say the guns I do it on shoot well but hey also get other things done .
I have also played with material on the top of the carrier so it fits tight tot he hole in the rsb as it locks up.
the trick is to get every thing so it will cycle yet lock up the same place every time. then theres the whole getting the bolt tight in the carrier .
see my accurising the ak thread.
This gun had only minimal work done to it. the barrel is really a light profile lighter than a standard AK with.
I built it to shoot things close up an to be able to carry it all day.
since its a screw build Im going to build a heavy target barrel assembly . ill be able to use the 223 bolt just swap the trunion an barrel stuff. I need to find a extra trunnion .