Rechambering 7-08 to 7-08AI

[thumper3181]

I have a Ruger American Predator gen2 in 7-08 and I am wondering if it's possible for a gunsmith to ream the original chamber to a 7-08AI without sacrificing any length. I want to see if I like the cartridge before I have a custom rifle built for it first.
Thanks
Frankie

 

[NZ_Fclass]

There's no reason why not, in fact it's an easy job...but there isn't a lot of gain in powder capacity over the standard brass. I guess the action length is too short for 280AI or 7x57AI, both of which would give a massive boost in bullet weight and velocity - and there's factory brass from the 280AI from Nosler.

 

[ggshoots]

Very simple, shorten the tenon a little then rechamber. Should be plenty of threads for the nut. Do yourself a favor and get rid of the round nut. You will gain a little speed but much better brass life without trimming. That would be a good rifle to experiment with.

 

[Kurz]

Some smiths turned back the barrel tenon one thread, reset the shoulder, and chambered the barrel with a headspace dimension .004″ short of minimum so that the parent cartridge would be supported at the neck shoulder junction and provide improved accuracy and less case stretching when fire forming. Resetting the barrel one full turn also allowed the existing markings on the rifle’s barrel to remain in the same spot when assembled. The only real downside to this method is that it requires a lathe, while the original method of improving a chamber can be accomplished by hand.

If you want the information for yourself, do an internet search and you'll find several good articles. Otherwise, find a gunsmith who understands the process correctly and let him have at it.

Too many believe wrongly that AI is simply for getting more velocity. Reality is that the improved shoulder creates a better chamber for burning powder than the older slope shoulder cases. You get more efficient burning and a larger number of potential powders to use. The steeper shoulder also changers the position of the flame point with regard to the throat (a good thing).

Do some reading then find a qualified gunsmith.

 

[STOMP442]

People say not to bother with improving the 260 either because there is not much gain but I will fight them tooth and nail on that one. Honestly you can expect at least 100fps improvement on velocity which puts you very near 280 Rem or 284 Win velocities while staying extremely efficient on powder usage. Brass will last forever, very little trimming and you will have something different that most people don't.

 

[Sniperhandle]

Because the Ackley datum is 0.004 shorter, The barrel needs to be set back one turn. Most people do not understand this. You can't just ream the chamber out to AI because the chamber will be too long and you will get case head separations.

So the barrel will need to be removed and the tenon re-machined to give a new starting point for the AI reamer. You can use the parent case 7mm-08 go gauge as a NO go gauge. When headspacing ream until the 7mm-08 GO gauge just lets the bolt go about half way to closing just as you would with a no go and it will come out perfect every time.

Side note:

A 308 Win GO gauge can be used for this as a NO go.

 

[DaveTooley]

Because the Ackley datum is 0.004 shorter, The barrel needs to be set back one turn. Most people do not understand this. You can't just ream the chamber out to AI because the chamber will be too long and you will get case head separations.

So the barrel will need to be removed and the tenon re-machined to give a new starting point for the AI reamer. You can use the parent case 7mm-08 go gauge as a NO go gauge. When headspacing ream until the 7mm-08 GO gauge just lets the bolt go about half way to closing just as you would with a no go and it will come out perfect every time.

Side note:

A 308 Win GO gauge can be used for this as a NO go.

I don't like using standard gages for AI chambers. Does it work, sort of. The neck diameter as well as the neck/shoulder junction radius will then affects HS.
Ask me how I know. I have 243AI reamers with three different neck diameters. I used a shortened standard 243 Win gage. That made the phone ring. I use only matching shoulder angle gages now.

I love my 7-08AI

 

[Sniperhandle]

I have used just a standard go gauge for the parent case as a no-go for the AI several times and it worked perfectly. The standard go gauge is the 0.004 shorter so it works.

I would think shortening a go gauge would cause problems.

 

[DaveTooley]

I have used just a standard go gauge for the parent case as a no-go for the AI several times and it worked perfectly. The standard go gauge is the 0.004 shorter so it works.

I would think shortening a go gauge would cause problems.

Supposedly it's to get a crush fit but as I said, neck diameter influences HS. Sometimes it makes the phone ring.

 

[Sniperhandle]

Dave,

You know I'm one of your biggest fans on here, And I am certainly not going to argue with you, But I am having trouble figuring out what you are saying. Headspace gauges don't have necks? I don't understand what you are saying?

 

[DaveTooley]

In my case having AI reamers of the same caliber, with different neck diameters and then using a standard 243/308 etc gage will yield different headspace numbers as measured from the datum line on the shoulder. Just an example. A 243 AI with a neck diameter of .265" will have a different HS than a reamer with the standard SAAMI neck diameter of .2783". The larger neck diameter makes for a shorter chamber while the smaller neck yields a longer chamber. Then add in the possible difference at the neck shoulder junction with the radius on each reamer.
Another way to look at it. Take two ring gages. One measuring .265" the other .2783". Insert anything tapered. The .265" ring gage will contact the taper sooner.

 

[Sniperhandle]

Ok, Thank you for explaining it that way, Makes sense now, I see now how neck diameters can change things.

 

[jackieschmidt]

Because the Ackley datum is 0.004 shorter, The barrel needs to be set back one turn. Most people do not understand this. You can't just ream the chamber out to AI because the chamber will be too long and you will get case head separations.

So the barrel will need to be removed and the tenon re-machined to give a new starting point for the AI reamer. You can use the parent case 7mm-08 go gauge as a NO go gauge. When headspacing ream until the 7mm-08 GO gauge just lets the bolt go about half way to closing just as you would with a no go and it will come out perfect every time.

Side note:

A 308 Win GO gauge can be used for this as a NO go.

I have done a couple of Ackley 30/06 Remingtons for friends, both Remington Sendaros. I pretty much do what you do, I set it back so the barrel lettering comes out correct, then establish the AI chamber.
Of course, the bolt nose counterbore and tenon length have to be recut to the correct length.
I did not use a reamer bushing on either, I let the reamer follow the chambers body, as on either factory barrel, nothing really ran true enough to do any more than simply keep the chamber where it was originally.
I just used a new Lapua 30/06 case as a gage, I gave it a little crush, so to speak.

 

[Sniperhandle]

My 6.5x55AI

I feel just a slight resistance when chambering un-fireformed parent brass.

 

[troupe]

I don't like using standard gages for AI chambers. Does it work, sort of. The neck diameter as well as the neck/shoulder junction radius will then affects HS.
Ask me how I know. I have 243AI reamers with three different neck diameters. I used a shortened standard 243 Win gage. That made the phone ring. I use only matching shoulder angle gages now.

I love my 7-08AI

Tommy Roupe here Dave, I have been thinking of giving you a call on one, I plan on being in the 120 to 150 range bullets, Nothing bigger, Deer and bear at the most. I had purchased 7 SAUM brass, but I just thing I need it, I will text you first to see when we can talk.

Tommy