Just wondering how difficult it is to convert a 257 Roberts to an Ackley Improved. I spoke with a gunsmith and he said it was a pain in the azz. The gun is a Kimber 84M classic.
Also what is the procedure?

To do it right, the barrel needs to be set back one thread before rechambering, in order to provide firm chambering for standard brass.

If the AI reamer is just run into the chamber enough to clean it up, .257 brass won't fire-form correctly unless you seat bullets out firmly into the lands, or neck-up the brass to form a "false shoulder" to hold it firmly against the firing pin's fall. If you try to just fire-form .257 ammo (whether handloads or factory) some probably won't go off, while those that do may stretch so much near the head the brass is ruined.

Then there's the question of whether the AI cases will feed correctly from the magazine. If they don't, there's more work.

Yet another factor is that when loaded to the same pressures, the AI version gets AT MOST an extra 100 fps over the standard .257, which you'll never notice in the field, either in trajectory or killing power.

I know all of this from experience with more than one .257 AI. If you really, truly want more "power" than the standard .257 Roberts can provide, then buy a .25-06 or .257 Weatherby.

Oh, and welcome to the Campfire!

Thanks.

I already have an Ackley improved. So I'm already set up to reload for the AI. I do have a 25/06, but it's real heavy and not a pleasure to carry in the woods.

it could be a real pain! Mr. Mule Deer is correct but he gave you the readers digest version as to what's involved.
"set the barrel back" involves pulling the barrel, re machining the tenion so it indexes properly again,cutting the new chamber,re-installing the barrel and all this without marking either the barrel or action up in any way so it won't have to be refinished.
now it is back together,the 64 thousand dollar question, will it feed with the new sharper shoulder? to make it right will be more money on top of the previous work.
I know you said that you are already set up to reload the AI configuration but a set of dies will be cheaper and quicker unless you have to have the AI version.

Or you could just use Hornady SuperPerformance ammo (if they make it for that caliber) for the increased MV if you don't want to reload.

FYI, in my .30-06, at 300 yards, the 150 gr. SP groups 6 inches higher and 3 inches right of same weight factory Corelokts, so there is something to the claim...

3 shot groups with either hover right around one inch at that range, tho the Corelokts seem to average just slightly larger- maybe up to .25 inch over the SP.

But that was only a sample of 2, 3 shot Corelokt remnant, so it's not a large sample size.

shooter42,

Just curious, but if you cut off one thread of the barrel, won't that also shorten the barrel shank and thereby change the barrel profile in terms of how well it matches the inletting of the stock?

In my 22" .257 Ruger, the max charge of Hybrid 100V gives me a little over 3200 fps with a 100-grain bullet, which is plenty of zip for me.

Yes setting the barrel back can leave you with a larger gap in your barrel channel.

I have owned 3 257 Roberts 2 were AI one was done right 1 was not. The advantage to me at least was less case trimming, and the ability to match fast standard speeds without redlining at max pressures.

Accuracy seemed better when it was AI.

All said if you like your rifle in standard and are happy with it leave it alone, std chamber will maintain a higher resale value also.

Shooter42

I just chambered 4 of the improved rounds in the magazine. All of them fit properly. And the bolt picked them up from the magazine.

las

Nobody makes ammo for it.

.

The point Las was making is that you could just buy Hornady Superperformance ammo for the 257 Roberts.

Steelhead

Its going to be a 257 Roberts "ACKLEY IMPROVED" and nobody makes amunition for the improved chamber.

I know that dipshett, again the ever loving point was you could shoot some souped up 257 Roberts ammon.

When I was fire forming factory ammo in my other Roberts. The group size was 4 to 6 inches at 100 yards. So while it may shoot factory ammo Accuracy was pitiful.

Since you already have a 257AI, I would have assumed that you would know what the process was from your first conversion.

What Mule Deer wrote is, as usual, spot on. I don't know what the TPI specs are for the Kimber barrels, but a barrel set back of one full turn for most common barrels runs in the 1/16" (0.0625") to 1/20" (0.05") range. After being set back, there will be a slightly larger gap between the wood and the barrel that will probably not be obvious to anyone but you and the 'smith who does the work. This is very straight forward work, so I can't imagine that a professional 'smith would take more than a few hours, like less than four, to do the job.

260

When I did the first conversion I simply dropped the gun off with the gunsmith. And when it was done I picked it up. The gunsmith never explained the process and I didn't ask.

leonen,

others have answered some of the issues. move the barrel back to get the proper headspace on the Ackley chamber will leave the barrel stock gap larger but not by much. if the cartridges feed already then you are ahead of the game. you just have to decide to do it if you want the AI version.
for what it is worth I have a ruger #1 I did up in the 257AI just because I wanted to.

Then this conversion should be the same. Drop the rifle off with your preferred 'smith and write a check when you pick it up. If your 'smith thinks that a straight forward job like this is a PITA, maybe he just doesn't want the work.

BTW, I have several rifles with AI chambers, so I'm not anti-AI.

If a re-chambered 257 AI does not have a crush fit on a factory 257 Roberts it was not done right. Should have resistance when you close the bolt.

A Kimber 84 is a little more difficult to set back than a Remington 700 but does not approach the PITA level. The barrel has a coned breech and extractor slot that have to be dealt with but that just means a little more expensive job.

Here's what the gun looks like. AAA French Walnut.

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Brilliant