I agree with all the posters above about checking everything else. It's not likely that you've got a shot out barrel and everything else is fine. Chances are it isn't shot out, either, but "cleaned out". Those steel cleaning rods do a lot of damage over 60 years! Chances are you'll find wear elsewhere also.
Replacing the barrel does not need to cost you an arm an a leg. First of all, what barrel is on there? My 1945 had a 1945 barrel (original to the receiver) and was, in fact, cleaned/worn out. The muzzle, especially, would swallow the neck of a 30.06 cartridge. You're supposed to see about 1/8" of the bullet! Counterboring was not an option.
So, I started the hunt for a duplicate replacement. The first place I'd recommend looking is at, of all places, eBay. Right now there are 26 auctions occuring there. Just do a search for "M1 Garand Barrel" and you'll see them listed. There are a bunch of years to select from and prices are very reasonable. Once you find one and get it, just find a reputable smith who has worked on a lot of Garands. They usually aren't too hard to find but ask questions. This isn't your basic "Remchester" after all. If you're unsuccessful, then look online for someone reputable and simply ship it off for the swap.
I did all of that to my Garand paying only $56 for the barrel (wonderful condition!) and had an armorer in PA do mine. He's well known in his area as a great Garand smith and only charged me about $50 including shipping both ways to have mine done. I can easily shoot 2" groups at 100 yards with it an iron sites. It performed extremely well at 200 yards, too, at Camp Perry this past Summer and also was inspected by the CMP guys and I passed muster. I placed 9 shots within 4" in the center from the prone position, slow fire, iron sites with that barrel. I was really surprised. (Don't ask about the 10th!)
Fortunately the Garand is one of the best documented rifles on the planet and parts are easy to come by. Just don't fall into the trap of putting on an aftermarket barrel. Stick with a GI replacement and you'll preserve the history and restore the accuracy of that great firearm.
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