Rifle chamber

[Dbl bbl]

Make a long story short. I got burned on an old M70 rifle that was marked 257R and turned out to be a 25-06 Ack. Imp. Was never restamped. A regular 25-06 does not chamber which I understood it should in an Improved chamber. Was the chamber somehow cut wrong? Could it be "re-cut" to accept regular 25-06? It would be much easier in fire forming cases.

 

[brickeyee]

You need a chamber cast to figure out exactly what you have.
An Ackley chamber has the minimum headspace for the parent cartridge (the 'go' gauge is the AI 'no go') to ensure headspacing during forming.

You would have to set the barrel back (again) to try and alter an AI back to the original, possibly a couple turns.

 

[Scorch]

You cannot change an AI chamber back to 25-06, the parent cartridge has more body taper and you will have a hard time getting the chamber to clean up. First, if you are interested in keeping the same barrel, you need a chamber cast to determine what cartridge you have. There are numerous 25-caliber wildcats that use a 280 Remington case as the parent case (the shoulder is .050" farther forward than a 25-06), and there are the Gibbs cartridges that have a 1-caliber neck, with the shoulder .100" farther forward than a 25-06. My recommendation would be a new barrel.