With every rifle barrel I get in here I manually push some pellets from breech to muzzle with a brass rod to make sure the breech is slightly tight, the bore opens up and is consistent after that until it reaches the tighter place at the muzzle crown. By the latter item, I'm referring to a barrel choke--assuming of course that the barrel is supposed to be choked.
I had one--I repeat one--barrel that had a very tight spot in it about 3-4" down the barrel from the breech. I marked the rod where the tight spot showed up, screwed on a brass brush loaded with JB Bore Paste, and gave the barrel something like 5 or 6 good back-and-forth 'scrubs' at the tightest spot--probably over a 1" length. Then I repeated the exercise with a brush again, centered over the tight spot, but this time for a wider length like 2 or 3". Then I gave it something like 2 gentle scrubs from just inside the breech to the muzzle crown. Last came few pushes with JB Bore Paste on a cotton patch. If you get what I'm saying, I wanted the transition from the previous tight spot to be gradual and (hopefully) uniform in diameter.
I tried the pellet push again when I was all done and the tight spot was gone--I didn't feel anything irregular or any resistance anywhere along the length of the barrel, excepting of course where it got tighter at the choke. That is, the tightest spot in the barrel was at the choke in the muzzle crown which is exactly what I was after.
The rifle was very accurate when I tested it afterwards so I felt my work passed the acid test. HTH.
Safe and Happy Shooting!
Ed Krzynowek, The Airgun Tune-Meister
"We can rebuild the squirrel. Make him stronger, faster...We have the technology"---Skyler M.