Not sure if this is of any value to anyone in this thread but, long story short, I'd probably never want a rechambered rifle again.
I am in general agreement with your .02, especially when the job is a poorly executed economy or desperation measure. The 8x57 Carcano and 6.5 Vetterli conversions come to mind. However the 7.62x51 M1 Garand conversions do not usually fit into this category -- unless hopelessly bubba-ed! And FWIW, during most of the Garand's development cycle it was chambered in .276 Pedersen.
There were three typical methods for
converting (as opposed to
rechambering) a 30-06 M1 Garand to 7.62 NATO:
1) Shortening the barrel from the breech by about .5" and then recutting a new chamber (which was actual rechambering)
2) Fitting a steel insert inside the existing chamber, thus reusing the original barrel with minimum cost
3) Replacing the entire barrel with a new one.
The US Navy started with the insert method, and eventually opted for replacement barrels.
The most problematic method was the use of a chamber insert. This was known to occasionally work loose and eject stuck to a spent case. Occurances were seldom catastrophic, but they could put the rifle out of action until serviced.
Shortening the barrel and rechambering had the advantage of reusing all of the original components of the original rifle, but the disadvantage of requiring the op rod, spring, buttstock and handguard be shortened to match. The Beretta factory offered this conversion as an economical way for NATO countries to continue using existing stocks of Garands, and at least Italy and Denmark paid to have quantities thus altered. Columbia also did a small number of similar conversions domestically:
Installing a new replacement barrel was the simplest and safest route since only one component had to be replaced, but manufacturing and installing a bunch of brand new barrels can get pricey, especially at a time when the armies were in the process of switching to infantry rifles with removable box magazines.
In all three methods, the conversion also included alteration of the gas port to match the different pressure curve of the 7.62 cartridge. In addition, a block of some kind was typically inserted into the front of the magazine well to prevent loading a clip of 30-06 cartridges -- this was a safety measure and had no effect on feeding the shorter cartridges. Here's a vid of a Danish 7.62x51 Garand running the shorter ammo flawlessly: