Do not atttempt this. Find a gunsmith.
This is best left to a factory trained gunsmith.
Correct terminology is 'inner magazine tube assembly.' The BAR22 and BPR22 used the same part, we occasionally have them for around $23.
Try want ads, for sale ads, gun shops, gun shows, estate sales, garage sales, pawn shops, egunparts.
MidWay USA or Brownell's Use Browning's site. Very good info.
Matt Eastman's book has a pretty good schematic.
http://stevespages.com/pdf/browning_auto5.pdf also, try e-gunparts.com
It could be due to a few different reasons. Recommend that you contact Browning for service. The link is below. Also take a look at the schematic and the Challenger II owners manual.
it is a model which is schematic
what schematic heart
There are many schematic symbols.
a schematic circuit is a diagram that show you how a particular circuit works