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Old September 20, 2011, 10:49 PM   #1
rbursek
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257roberts to a 257AI

Can a rifle in 257 Roberts that has been fired be reamed to a 257AI? I am looking at a factory win to do that in.
Bob
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Old September 21, 2011, 12:05 AM   #2
Scorch
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Absolutely. Set the barrel back one thread (if you want to do it right), ream the chamber to AI, and voila! The 257 Roberts Ackley Improved! Actually, the 257 Roberts is one of the best to improve.
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Old September 21, 2011, 12:03 PM   #3
kraigwy
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If I'm reading this right, you want to go from a 257 AI back to 257 Roberts.

Yes it can, but why. Regular 257 Rbts can be fired in the 257 AI with no problems.

Personally, I'd leave it alone.

You'd have to set back the barrel as mentioned, then re-chambered/headspaced for the Roberts.

My main hunting rifle is a 257 Roberts. I see no reason to convert it to the AI, but if it was a 257 AI I would see no reason to change it back.
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Old September 21, 2011, 01:15 PM   #4
edward5759
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I have both, can tell no real difference!
The only way is shooting across a chronograph.
Shooting up to 600 yards both give the same performance.
I have shot deer with both under 200 yards with good kills.

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Old September 22, 2011, 01:44 AM   #5
rbursek
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Thanks Edward######, I gave my 257AI to my son with DRT kills on deer and Elk with 115 grain Nosler partitions, but I assume with a regular Bob+ loads now it is not much slower then the AI. Too many people get caught up with FPS and all want them over 3000, look at the 7x57, 6.5sweed, all killers. I will stay withthe regular Bob from your crono advice. Thanks
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Old September 22, 2011, 03:51 PM   #6
edward5759
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I have hunted the open canyons of Arizona for 50+ years. Have shot a lot of different game from elk to jacks. My Bob has always delivered, I have had 270s and 25-06 blow through things the bob has always performed.
The bullet weights and velocity is just right!
Good luck.
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Old September 23, 2011, 11:50 AM   #7
Sevens
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Quote:
Set the barrel back one thread (if you want to do it right),
I know VERY LITTLE about center fire rifles.
Why would you set the barrel back one thread to do this?

Why would you do anything other than make a slight alteration to the chamber?

I'm curious to learn more!
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Old September 23, 2011, 12:00 PM   #8
Scorch
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Quote:
Why would you set the barrel back one thread to do this?
Short version:
To make sure you clean up the whole chamber.

Longer version:
The cartridge's datum line is in the middle of the shoulder. Envision a 20 degree shoulder and a 40 degree shoulder. Since the datum line is a specified dimension of the case, the shoulder angle will pivot around this datum line. If you cut a chamber without setting the barrel back, you almost always have a small but noticeable area at the base of the neck that is at the old angle. This will be noticeable in the fired brass, it will look a little like a Weatherby Double Venturi shoulder. It probably won't make a bit of difference, but if you are going to recut a chamber, recut the whole chamber. The reason you set the barrel back a full turn is so that barrel markings and/or sights are in the right place again.
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Old September 23, 2011, 12:06 PM   #9
Sevens
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Got it!
I had a wild idea to maybe have the chamber on my Super 14 Contender in .223 reamed to an AI... but it shoots so well that I can't really justify the expenditure or a tangible reason for actually having it done.
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Old September 23, 2011, 08:43 PM   #10
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I see it as spending good money on a non-existence problem.

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Old September 24, 2011, 08:26 AM   #11
Harry Bonar
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257AI

Sirs;
I agree with Scorch - this gets rid of all the old chamber and the 257AI is a very, very good varmit - or big game cartridge!
Scorch has the right isea.
If you simply run tht reamer in your old chamber you can get lengthwise chatter and by doing what Scorch said you are very much likely not to!
Harry B.
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Old September 24, 2011, 10:45 AM   #12
F. Guffey
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257 Roberts to 257 Roberts Ackley Improved.

There are 3 257 Roberts AI chambers, first there is the 257 Roberts AI chamber cut in a new barrel, if the new barrel is said to be short chambered, determiner 'how short'.

The 257 Roberts AI has a longer neck than the 257 Roberts meaning the neck shoulder juncture on the AI version is further back than the standard Roberts. By design this difference allows standard 257 Roberts to be fired in the Ackley Improved chamber, when chambered the standard 257 Roberts case neck shoulder juncture is sized (head spaces), when fired the rest of the shoulder and case body is sized/formed and the person pulling the trigger becomes a case former, or is that a fire former?

Then there is the person that knows the difference between the two chambers and understand by advancing the reamer all of the original chamber can be removed and be replaced with a chamber that is longer from the bolt face to the shoulder of the chamber, by as much as .020 thousands, depending on the receiver design, methods and techniques change when forming cases, remember Hatcher became a fire former by accident, With the longer chamber fire forming is not recommended. At this point the shooter must become a case former first and a fire former second, I have the 257 Roberts AI reamer and dies, with the feeler gage I can form the shoulder distance from the head of the case head in thousands anywhere I choose to place it, meaning I form first then fire, after firing my cases become once fired cases.

Then there is the 'set the barrel back' that involves a lathe, barrel vise, action wrench, and someone to operate all that equipment.

Everything listed above is relative to the 30/06 Ackley Improved, I have the tools, lathes, reamers and dies and more than one 30/06, so I chambered one to 30 Gibbs, the reamer removes all of the original chamber, the shoulder is moved moved forward .207 thousands, in my opinion that leave the neck too short, by design, their design, the neck is shortened to .127, I say too short because others say the 300 Win Mag neck length is short at .264 plus a little or - a little.

Anyhow, chambers that benefit the most by going to the Ackley Improved is the 257 Roberts, 30 H&H, 30-40 Krag, 303 British, back to receivers, not a good ideal to use the 30/40 Krag or the 303 British Enfield. For the 303 British chamber the P14 is a better choicer.

F. Guffey

Last edited by F. Guffey; September 24, 2011 at 08:58 PM.
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Old September 24, 2011, 08:57 PM   #13
F. Guffey
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Forgive, the shoulder of the Gibbs is .207 forward of of the 30/06.

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