I have a remington 700 chamebered in 25-06 -- I was wondering if this could be Ackley'd without rebarreling or without taking metal off the tenon?

For best results, I think you're gonna want to set it back a thread or two. You can use the same barrel, but it will involve a little lathe time by your 'smith. Setting it back insures that you get a good "firm" headspace, while fireforming, to ensure that the case isn't driven forward with the firing pin strike.

I've built a few 25-06 Ackley improved guns and It is a darn good idea! you will get about 200-300 fps more from the Ackley improved version. Accuracy also usually improves. The conversion requires that the barrel shank be moved foreward so that the reamer can cut the new Ackley chamber shoulder, neck and throat properly. The rear of the barrel, thus, needs to be shortened and this means a thread or two must be removed. A new barrel shoulder has to be made to re-establish the correct barrel shank length and very importantly, if you have a gun with open sights on it, the barrel timed so that the sights line up properly. This is simple only if you know how to do it. Headspacing is done such that a factory 25-06 will be supported by the shoulder/neck junction of the new Ackley chamber and will fireform properly on firing.
With 87 gr bullets you can see 3600-3700fps out of a 25-06 IMP which is just slightly behind the .257 WBY.-Rob

Hey'
I purchased a Tikka in 25-06,and did a 25Gibbs.It worked out very well.I also like the AI,but I think you get a bit more powder capacity,because of the short neck on the Gibbs.
1geejay
www.shooting-hunting.com

I would agree that setting the barrel back by a thread or two may be a good idea in some circumstances, but is not absolutely necessary for the .25-06 Improved conversion.

The main reason to set the barrel back is that the factory chamber is probably cut pretty sloppily (overly large). This means that unless you set the barrel back that the new reamer won't clean up the old chamber. If, however, the original chamber is within proper limits, then the reamer should clean it up fine. IF headspace is a bit too long for the factory cartridges, this is important only if the shooter intends to utilize the factory cartridges for fireforming. Otherwise, pre-headspaced fireforming loads can be made from something like .30-06 brass and can be made to fit the chamber perfectly anyway.

The .25 Gibbs, on the other hand, is substantially larger in shoulder diameter and has a shoulder further forward than the .25-06. It should be unnecessary to set back a .25-06 barrel when rechambering to this round.

Larryb-There are two reasons to cut a new barrel shank. The first is that if you try and ream a factory chamber to an Ackley version without cutting substantial metal out you invariably wind up with chamber rings and other chamber anomalies that can and will effect accuracy. The second is that one of the main reasons to make an Ackley anything is to be able to use factory cartridges in fireforming. To do anything else results in a non-standardized wildcat with chamber flaws that could actually be dangerous in your hands or that of a subsequent owner. This is not a good idea. Any competent gunsmith who has a Lathe and can ream a chamber has enough machining ability to face a barrel, make a new shoulder, time the barrel and do the job right. If anyone tells you differently run, don't walk away.-Rob