Bill: those distortions are very common in mass produced rifles and barrels. You will find distortions like that where the barrel bands are installed, where the front sights are installed, where the barrel is cut for rear sights, cut for attachement fixtures, or stamped with letters/numbers.
Does this affect accuracy - some say no, others say 'very much so'. This does not just happen with big bores, you can find it in most any rifle barrel.
I believe that such constrictions or distortions, as well as roughness on the lands and in the grooves can adversely affect accuracy and hence, the need for 'bore-lapping'. If ya'll want to drop on down to Veral Smith's forum and read what he had written about 'bore-lapping, or fire-lapping', you are in for a very educational read.
The process of 'bore-lapping' uses soft lead slugs sized to the bore diameter you want/need that are impregnated with a very fine grit. These slugs are fired down the barrel with just enough powder to get them out the end so as to impart a 'controlled wear' to the bore. This 'controlled wear' removes those distortions caused by banding, clamping or stamping and also removes any roughness found in the lands/grooves. A properly 'lapped' bore will be so shiney that it will be difficult to discern the rifling with a strong bore light but what you will see is a bore that is 'true' and will give you the best accuracy it can give.
I have bore lapped a bunch of rifles. My worst case was a Winchester M94AE in 444. This thing would absolutely not shoot cast bullets into anything that would resemble a 'group' at 50 yds, so I bore lapped it according to Veral Smith and now use .432 cast slugs that groups to one hole (with more than one shot I might add) at 100 yds. The difference is phenomenal and I have enjoyed this level of success with many other rifles. Ya'll really ought to go read Veral Smith, it's a eye-opener. HTH.
