I can't see why there would be any effect, but I doubt anyone really knows. I've read about everything about shotstrings and have given up on them anyway, beyond the fact that in trap, the shorter the better.
I would call Tom Wilkinson, he has done work for me and it seemed to be very efficient. He probably knows as much about barrel dynamics as anyone in the business. 919-603-0167, Hope this helps, Roy A. Morton
I know for sure if you have a gun with a messed up forcing cone having someone recut it will help your patterns a bunch, did for me on a 303, it looked like I had went to a tighter choke when I got it back.
A backbored barrel may reduce the effect of barrel scrubbing on the shot cup, which would pass through to an extent to the shot, and thus would reduce the contribution that barrel scrubbing makes to pellet deformation. A backbored barrel may also allow the shot to align better before entering the choke, which in turn might result in less deformation of some pellets. Deformation of pellets is one of the primary reasons for shot stringing.
Another reason for shot stringing is differing sizes/weights of the pellets. If you're shooting 7-1/2's, the shot size could be anywhere from just larger than 7 to just less than 8. How tight the tolerances are for shot size obviously depends on the mfr. A pellet that is close to 7 is going to keep its momentum longer than a pellet that is close to 8. A backbored barrel can not have any effect on shot stringing due to loose tolerances in pellet size.
Regardless of the effect of backboring in theory, how it works in practice will depend on the actual gun. The only true basis for judging is testing before and after. Then the actual results can be quantified.
As to whether backboring in general works to raise scores, all I can say is that magic wands come in all forms.
As much as I like to argue a point.. I've seen no real effect on shotstring..What I do see.. is when a barrel might be out a little..A person like Tom.. or Stu can use the extra metal to make the barrel perfect.. That results in a better pattern than one that is slightly off..less pellet deformation..and in my case..I don't care for screw chokes..and can gain "choke" for the 24 gram shells I enjoy shooting. Add to that..reduction of weight..which is a big plus in bunker and sporting clay shooting.. I've been told that full chokes have shorter shot strings than more open chokes.. Most of my chokes start out at .028 and end at .055.. I like seeing inkballs..or crushing a 65 yard target in bunker.. While not every barrel needs a barrelsmith..having a good barrelsmith look over you barrel.. and patterns could be very useful.. I'd venture a good guess that the winners circle is litered by barrels that have at least been fully checked and adjusted..by good barrelsmiths. Every barrel I own that Tom has worked on is excellent.. and Stu Wright has tackled some really difficult jobs for me..and each and every one of them came out perfect..and target crushing.. When all women look the same.. all barrels will be the same.. Until then..the ugly ones need a little help.. As long as barrels are mass produced..you'll have ugly ones..As long as a gunsmith tries to do the work of a barrelsmith.. you'll have ugly ones.. AND.. as long as Brownell sells backbore reamers to the public.. You'll have REAL ugly ones.. All Good.. Mike