7.62 M1 Garand sticky chamber

[boatbod]

After recently acquiring an M1 with a 7.62x51 barrel I found out that I'd bought a project rather than a finished gun. As it turned out, the short chambered barrel had been installed but never finish reamed/headspaced. Being the practical sort, with a modest engineering/machining background, I figured I'd obtain a pull through reamer & a set of gauges and complete the job myself. After lapping the bolt lugs and doing the reaming I ended up with what I thought was going to be a good chamber that nicely closed on the go gauge but not on a nogo.

After a trip to the range it seems I've got several problems to work on. They could well be caused by the same underlying issue.
i. Short stroking frequently. Maybe 85% of shots require manually cycling the bolt.
ii. Extractor ripping case rims sometimes.
iii. One complete failure to extract requiring a cleaning rod to knock the casing out.

Having examined the fired brass and what I can see of the chamber, it looks like there are machining marks in the rear half of the chamber that are being transferred to the brass making it extremely sticky and hard to extract.

The attached photos show two fired cases - the black one I covered in magic marker before dropping back in the chamber and letting the bolt slam home. Had to lever the bolt open to get it out again... I can see the majority of the rub marks correspond to the series of rings seen on the second casing which I polished with emery cloth.

If I'm right about the sticky chamber causing the short stroking, it should just be a matter of polishing it, but can this realistically be done without removing the barrel from the receiver?

Comments and suggestions most welcome!
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Ammo was a mixture of commercial 150gr .308 and Peruvian FAME 147gr 7.62x51.
Gas port in barrel was measured at .096"
Tilt test passes
I haven't gauged the gas cylinder or mic'd the piston yet.
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Thanks
/boatbod

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