criterion garand barrel

[AKA Hugh Uno]

Hugh, do you have one of these barrels or are you just guessing?
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Your INITIAL question (i.e. "what can I expect from XX commercial barrel") rests upon a rather weak premise. You seem to expect a certain degree of inherent accuracy, and/or superior accuracy from the barrel alone. BULLET is FAR FAR more important than barrel.

As far as accuracy goes, even from a Krieger USGI/JCG legal rifle, truly superior as this may be, I would never "expect" more than a QUARTER MOA advantage/improvement over a crisp tight new USGI SA barrel. If these barrels actually offered significant inherent accuracy (say more than 1/2 MOA), everyone would use them at Camp Perry and the winners circle would have NOTHING else. Thankfully, that is NOT the case.

HEAVY match barrels from Douglas or Krieger may have a bit more inherent advantage because they are STIFFER, but in a fully tuned match gun, the difference between say my Clint Fowler match M1 with a USGI barrel and the exact saME rifle with a heavy match barrel would probably NOT exceed 1/4 MOA! The real; advantage with the heavy barel is that as the match progresses, the heavy barrel would heat up less and be a bit more consistent, plus wobble less (heavier), and likely stay accurate a few thousand rounds longer.

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Oh, and I have owned several custom/commercial barreled match M1s and M1As over the years and still do.