Ok, I know this is stupid, but, Is there anything else needed to be done other than running a chamber reamer in a 280 to make it an 280AI. Do you have to set the barrel back and totaly rechamber or just cut in new angles with reamer?
Nav

Navigator

All Ackley improved cartridges are designed to use a minus .004 inch head space. This is because the cartridge when being fire formed in the new chamber is only supported by a thin line at the neck shoulder junction. The minus .004 inch dimension is to insure the cartridge is well supported with a crush fit so the firing pin will not drive it forward, creating excessive head space when fire forming. After fire forming the head space should be near zero and the case fully supported in the front by the entire shoulder.

The headspace on your existing chamber could be as much as plus .005 inch. For this reason you will have to set the barrel back before rechambering to any rimless Ackley Improved cartridge.

Ditto you will need to have the barel set back about a thread and then the new AI reamer run in.

Andrew

Does this mean the stock is no good?
Nav

Only if it's wood... Just kidding.

The only time setting a barrel back might effect the stock, is if the barrel were specifically anchored or bedded to the forearm.
Malm

Good. You had me worried. I picked up a Brand New Remington 280 Mntn rifle with Detachable mag and would like to get a bit more performance from it. Thats why I thought about rechambering it to 280AI.
Thanks
Nav

I love my 280AI,....it is wicked accurate with evrything from 140gr-160gr bullets.

I seat a bullet about .006" into the lands,..with a light charge (38gr) of imr4895,..and drop the hammer,..voila fireformed case with growth from the neck/shoulder and not the case head. You won't be dissapointed in that caliber.

Even if it weren't the way these gentlemen have explained,..it would still make sense to set it backa bit and freshen up the chamber while reaching a brand new throat as well.