A whole lot of accuracy (or lack of it) has to do with the breech end of a barrel.
Originally fitted the barrel using a hard RN pellet for my test (Crosman RNHP's). Fed very smoothly, shot good groups but not outstanding..which I wrote off as shooting at night (from one lighted shed to another).
Tested again in day light. RN pellets still shooting "OK" but not great (not as well as when the barrel was on a QB). Tried other pellets...but none of them would feed worth a hoot. Couldn't get a WC into that breech except by luck.
Smoothing...longer "throat"...still won't feed full WC's real smoothly, but they do feed and are undamaged. Accuracy better (about equal to the barrel when on a QB).
Removed the barrel and did it all over again. this time, o-ring on the very end of the barrel behind the transfer port's spot and another just ahead of the transfer port's spot (hadn't drilled it yet). Lathed a band around the barrel between the two o-rings (a radial groove like a wide 0-ring seat) and drilled three smaller holes in that groove. Basically making 3 little transfer ports rather than one great big port (this is like the RWS850 barrels are made).
If accuracy is better, would take a whole bunch of shooting to prove it (and the difference would be fractional). Breeching is better/smoother (not a do-over job this time, so it ended up a bit neater).
Will say this:
1. If your accuracy is sour, it may have much more to do with the rear end of the barrel than the crown.
2. The radial groove/mulitple ports adds compexity but no major gains in either velocity or accuracy.
3. Lesson learned: Breech end should be made to handle well the WORST shaped pellet, not the best.
