Tuning Avenger .22 barrel questions

[my87csx481]

My apologies in advance. I may not be using the proper terms for certain features of an air rifle barrel.

I have a wood stock Avenger in .22. I'd like to try to get it to shoot better than it does currently. I've had the barrel removed, and I pushed a few pellets through with a wooden dowel. 

1. Problem 1: The transition from the chamber to the rifling (leade I think) is abrupt, and rough on the pellet, causing damage.
2. Problem 2: If there is a choke, it is about 1 to 1.5 inches before the end of the muzzle. After this point of being tight, the pellet is loose for the last inch or so.
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   As best I can tell, inspecting through the breech with an eye loupe, the cross section of the barrel would look like the image below.
   
   The ID of the barrel where the transfer port is (chamber?), is rough looking. The probe o-rings "seal" on this diameter. The transition from the chamber to the rifling is just as I have drawn it in the image, a 90 degree shoulder. It is also tight going through that shoulder.
   
   I don't have access to a lathe. But I do have a drill press. And I found some information regarding drilling a piece of wood to support the barrel on one end (kind of like a steady rest on a lathe), and chuck it up in the drill press chuck at the other end. So my plan is to polish the probe o-ring sealing surface a bit (cratex and a dremel, while spinning the barrel....or maybe just really fine wet/dry sandpaper and a wooden dowel). There were no visible burrs on the transfer port.
   
   But what do I do with the 90 degree transition? I know what I would do if I had a lathe (used to be a machinist, but for the aerospace industry).....is this fixable without a lathe? Are all the avengers like this? Any help with addressing problem 1 is greatly appreciated.
   
   And once that is fixed, I plan to polish the bore (felt pellets, JB bore paste and bright, etc.). But I'm not sure I will be able to polish enough to move the tight spot to the end, at the crown (but that could also be my ignorance talking, as I've never polished a barrel). Any thoughts on what to do with this?
   
   Maybe I should pay someone to modify a barrel blank to fit....but it's an entry level gun. Seems like too much trouble, and probably too much money, for a cheap gun.
   
   
   

 

[nervoustrig]

The sharp transition in the leade can be fixed with hand tools rather easily. For the beginner, the technique I recommend is a dowel with wet/dry sandpaper, same as you mentioned, except sweeping it in and out rather than with a spinning action. Doing it by hand, you can gauge your progress as you go based on how it feels. I go into more detail in my little barrel accurizing guide if you're interested.

https://www.gatewaytoairguns.org/GTA/index.php?topic=130555

Regarding the loose last inch at the end of the barrel, the preferred way would be to chop it off back to the choke and then apply a new crown. The only real alternative is to work the constriction with a poured cast lap, but I would only attempt it if the loose spot is very slight. The more material you have to remove from the constricted region, the more you risk altering the rifling profile. At some point you're doing more harm than good.

I think a poured lap is better suited to unchoked barrels. Here's a brief writeup of a QB barrel I salvaged:
https://www.gatewaytoairguns.org/GTA/index.php?topic=180011.msg156049546#msg156049546

 

[my87csx481]

Thanks. It was that guide (or a thread that linked to it, or maybe your DIY crowning guide) that gave me the "steady rest" solution for the drill press.

Looking at the parts schematic, the pellet probe o-rings should be 5.5mm OD in a free state. I don't know what the OD of the pellet probe o-ring groove is (yet). But I suspect the area I keep referring to as the chamber is not as oversized as I think it looks. I need to take it apart again, and get an accurate measurement before I can make a decision on how to proceed with the leade.

Also, waiting to hear back if I can get a replacement barrel....then no worries if I mess it up completely (well, mostly no worries).