Are some Green Mountain .25 Marauder barrels choked and some not?

[subscriber]

I used a round headed brass screw and lapping compound to clean up the crown.  McMaster part number for the screw:  https://www.mcmaster.com/#92453a535/=1b05f9z

The radius on the screw head is such that the resultant crown tangent right at the edge of the bore line has about a 120 degree included angle.    This is shallower than the typical small break-edge at 45 degrees.  Then; the radius rolls into a steeper than 11 or zero degree crown angle favored by many.  Anyway, considering the primitive method, the resulting "nozzle" seems OK.

If you are wondering why I went "so deep" with the brass screw; it was necessary to cut away steel nearer the barrel OD to reach the bore line with a 0.235" screw head radius.   I chose that size screw to ensure the bore line met the crown at a more obtuse angle than and included angle of 90 degrees.   Once I had cut away most of the original crown, I thought the small remaining annulus looked odd, so I kept going till it cleaned up. 

I used a rubber tipped 400 grit "bit" that measured .258" in diameter to polish the leade.  I first ground a 10 degree (radial) cone onto the rubber bit.  I figured that trying for a much shallower leade angle would be looking for trouble, considering I was holding my Proxon grinder by hand.

I left a hint of the original chamber mouth at the bottom of the lands, as I did not want to enlarge the already generous chamber.  If I had an appropriate chamber reamer I would have just cut the chamber .02 to .04" deeper...

For both the crown and the chamber I ran the barrel at 120 RPM (minimum) in my little ENCO lathe to try and diffuse my hand induced errors.  I don't have the tools required to set the barrel to spin with zero runout, otherwise cutting a new crown may have been the obvious way to go.  I managed to position the barrel so the lathe's chuck and barrel runout cancelled each other down to a TIR of 0.002".  The brass screw should have followed the bore axis in theory...

Used a cordless drill to turn the brass screw.  Ran it forwards and backwards, with the lath running opposite direction. 

Ran the rubber bit at the lowest speed of 5000 RPM, and gently "bumped" the end of the chamber until it looked about right.

Chambering pellets is smoother, with subjectively half the original effort.

Pellets pushed through the barrel have clean riflng marks.

[nervoustrigger]

subscriber, nice execution there!  Great picture that shows a clean crown transition.