Rechamber 6.5 Creedmore to .260 AI

crazymonkey said:

Your cutting it close with just .005 . That's just .0025 per side for a reamer . From a machinist perspective it's only do able if everything is perfect . The run out of the barrel will need to be zero to the bore dia and the reamer must be centered perfect. Usually we run reamer at .005 per side or .01 under . I'm a aerospace machinist not a gunsmith but it's the same principles.
Just re read the tolerance and .0005 is not enough stock . It definitely depends on the depth of the rest of the chamber cuts . We've run into chatter issues with step reamers having issues with not enough to prevent chatter as the first dia is usually the support for the rest of the cut.

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Rflshootr said:

It could, depending on how close, to true size, the original chamber was cut. If I were going to give it a whirl, I'd set the barrel back the length of the neck (.295-.300), then rechamber. You'd probably be better off just starting with a fresh barrel though.

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My math says it won't work without setting the barrel back. (if I made a math mistake, I will be glad to learn)

The chamber specs of the rim diameter are not the controlling point for this potential re-chamber.

The point .200 from the cartridge base datum line is the same in both cartridges .4714
From that point the CM body taper runs out to a point 1.4864 from the base where it is .463 in diameter (body/shoulder junction). That point is your controlling point. Your new chamber has to cut that point away.

The case body taper of the 260ai is 89.75836220196909 degrees. If you calculate that taper angle to the CM case/shoulder point, you find the 260ai reamer will be cutting a diameter of .4606. And that will be leaving a .0015" ring in your chamber.

Stay well,

If you could cut the threads off the barrel, then bore concentric in relation to the bore, then chamber, you have a fighting chance. Mis aligned bore in relation to the origional chamber kills the whole project.

If you are happy with 3/4" groups at 100 on the finished project, then you have justification for some mis alignment being ok....as long as you know that it is a crap shoot going forward.

Back to a factory sporter barrel contour likely does have enough material to cut off the tennon for a fresh chamber that is properly supported.

No, I don't have .243. No I don't have an action. This was a brain storming exercise to see what direction I should go. I was trying to go inexpensive with a simple rechamber.

I will likely purchase something with the plan to rebarrel from the start. That would also allow me to get a long action, which will really let the AI stretch its legs.

A A Ron said:

Back to a factory sporter barrel contour likely does have enough material to cut off the tennon for a fresh chamber that is properly supported.

No, I don't have .243. No I don't have an action. This was a brain storming exercise to see what direction I should go. I was trying to go inexpensive with a simple rechamber.

I will likely purchase something with the plan to rebarrel from the start. That would also allow me to get a long action, which will really let the AI stretch its legs.

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Depends on how far you want to seat bullets out. The new Remarms SA allows you to seat out to 2.950" with AICS binderless mags. But whatever you'd like to do.

I say go for it! I've done a few hand reaming jobs on old factory barrels when making fireforming barrels for wildcats. They never had to be great, just close enough. It's surprising how many of those actually shot really well. I've even intentionally run a reamer too deep by a few thousandths, or more, just to clean up an old chamber. These were all wildcats needing to for formed anyways, so there's no worry about someone getting in trouble because of the odd headspace.

FWIW, I was doing this with old barrels that I wasn't that worried about. Sometimes it's fun to just wing it and see what happens though.

lancetkenyon said:

AARon, that is not a SAAMI spec 6.5CM reamer, which all the factory barrels use.
View attachment 618449
View attachment 618451
View attachment 618452
View attachment 618443

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Lance, on the 6.5CM, looks like your comparing his CHAMBER spec drawing to your CARTRIDGE spec drawings. Need to compare chamber specs so it's apples to apples to see for certain. Given the body tpi on the two drawing Ron shared, if the 200 datum diameter is truly the same, the 260ai has more body taper so would be a smaller diameter along every point past the 200 datum line.

A A Ron said:

I will likely purchase something with the plan to rebarrel from the start. That would also allow me to get a long action, which will really let the AI stretch its lelegs.

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If you are still talking .260AI in an LA, you will have to get a custom reamer with a ling FB to get an OAL over 2.980" with a 140.
Like I said, standard FB in the .260 Rem Imp 40°/260AI is only .050".
I went with +.090" more, for a total of .140" FB and the 140 Hyb fits in an Accurate .308Win magazine without the binder plate at 2.972" COAL just touching the lands.

The PTG .260 AI reamer print I attached is the one I would use. Actually it is the one my gunsmith would use. I will give him a dummy cartridge with a bullet loaded long and specify how far off I would like it. I'm guessing if it is too deep he would throat in a separate operation.

The PTG is close to Lance's but there is a very small difference.

can1010 said:

your .200 line dia. isn't your problem the shoulder dia. is. creed .463, 260ai .460 you will have to remove a good portion of the Creedmoor chamber to clean up the shoulder with the smaller 260ai reamer. if you have enough shank left on the barrel to remove the threads and start over and the barrel is a quality barrel with low round count it might be worth it, high round count or factory barrel don't waste your time just save for a new barrel

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260 body length is longer by .070", so the shoulder junction is going to be less

260AI is a great cartridge but I don't think it is long enough to clean up that shoulder point. I run mine in a short action but my barrel is a 9 twist bagel so I don't run the long 140s but rather 140 SGK. It is a featherweight so 500 yards is my limit. The SG excels in this distance.