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Could you explain the mechanics of why a barrel setback is necessary after an AI reamer has been run in a factory barrel?
Thanks
Jim


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If the headspace is not on a rim or Belt, you have to set back...

An Ackley go gauge is shorter than a non-Ackley because the headspace moves from the shoulder to the should neck junction.
and it needs to be tight... so you can still fire non-Ackley improved in the rifle.

I.E. you are blowing Out the should when the AI reamer removes the metal, which can make too much headspace, or the thing may not even fire non ackley brass right.
This picture helps.

[Linked Image from ackleyimproved.com]

You can read the whole page here.
https://ackleyimproved.com/headspace-and-ackley-improved-cartridges/

Last edited by Spotshooter; 06/21/20.
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I'm not a gunwriter, but I believe there is a recent thread on this topic. Search for it.

The bottom line is that the improved reamer must be run further into the existing chamber in order to "clean it up" . The barrel must then be set back a bit in order to do this and still maintain correct headspace.

Some unscrupulous gunsmiths simply run the reamer into the chamber without removing the barrel from the action in order to save time. You end up with a chamber that is longer than specifications, and you have your own unique improved chambering. When this is done, the bolt will close on a no-go gauge, and headspace is too long. I have gone through this with two Ackley Improved chambers and such gunsmiths.


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Notice the base to the neck shoulder junction distance...


[Linked Image]

[Linked Image]

Last edited by Spotshooter; 06/21/20.
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Have seen more than one AI rechamber job fail to fire factory ammo--and even when "set back" they can fail to fire brass previously-fired "standard" brass, because it lacks the slight "crush-fire" radius at the juncture of neck and shoulder.


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Just go buy the cartridge whose performance you are trying to attain and save the grief. JMO


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I'm attempting to find how to rechamber a 6.5X55 TC Encore barrel in 6.5X55AI. According to the material Spotshooter has provided https://ackleyimproved.com/headspace-and-ackley-improved-cartridges/ it's not viable. A "setback" would necessitate a removal of the barrel mounting lug and rewelding it. Have a growing suspicion that it (6.5X55 to 6.5X55 AI) with a TC Encore barrel has been done.

Last edited by Rug3; 06/21/20.

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Originally Posted by WAM
Just go buy the cartridge whose performance you are trying to attain and save the grief. JMO


Well, yeah....

A related factor is that a lot of newer cartridges are ALREADY essentially AIs, with nearly parallel body lines and steep-angle shoulders.


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If you want a 40 degree shoulder on a 6.5x55 TC where you can't set the barrel back you just have to build 6.5x55 Improved, not an Ackley Improved. To form brass you have to open the neck to a larger size and the take it back to 6.5 and form a false shoulder for the case to headspace on. After that you can just use a set of 6.5x55 AI dies just being sure you you set up the dies so they don't push the shoulder back too far, There are a lot of improved cartridges that don't use a crush fit to be able to shoot factory rounds. Off the top of my hat the Gibbs line of wildcats come to mind.


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Rug,

You can get the appropriate headspace guages to figure out if it’s too deep.

If it is - Blueberry or EABCO barrel works could fix it for you.. by shaving some off the face of the barrel and moving the lug forward a few thousands... but first I’d do the gauge testing to see how far forward it is.
** remember 10 thousands is the max headspace you’d want, so you are probably a bit longer than you might want it but not to 10 if someone just ran a AI reamer in the standard chamber ... that is unless they moved the neck shoulder junction forward much.. Frankly when cutting a chamber you almost can’t feel a thousands or so unless you know what you are looking for and what you are doing, it’s the slightest of cuts.


OR

You can just not shoot standard brass in it and deal with the slightly longer head space by by neck sizing, and only bumping the shoulder...

Last edited by Spotshooter; 06/22/20.
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Can you also load long, into rifling to hold the standard case against to blow of the firing pin to fire form AI cases?

That’s a question, not a statement.......


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Blacktail53,

You can, but whether it works correctly or not depends on how firmly the case neck holds the bullet, and how hard the firing pin whacks the primer. Generally find it much better to have the chamber correctly cut for a crush fit on new brass, or to neck up and then neck down again to get a crush fit.

These days, however, I find the easiest solution is to use a factory round that produces the desired ballistics. There are so many out there these days, especially those with steeper shoulders to begin with, that I really don't see any point in fooling with "improved" cases.


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I'll throw this visualization into the fray. I drew this up in AutoCAD. The Ackley Improved Dimensions are from Ken Howell's book and are based on dimensions from the Speer No. 4 Manual. I believe this was before SAAMI standardization. If you don't set the barrel back you will end up with a fire-formed cased that has two shoulder angles (ask me how I know).

[Linked Image]




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Originally Posted by Rug3
I'm attempting to find how to rechamber a 6.5X55 TC Encore barrel in 6.5X55AI. According to the material Spotshooter has provided https://ackleyimproved.com/headspace-and-ackley-improved-cartridges/ it's not viable. A "setback" would necessitate a removal of the barrel mounting lug and rewelding it. Have a growing suspicion that it (6.5X55 to 6.5X55 AI) with a TC Encore barrel has been done.



Don't know about this one but years ago, I had a 7x30 waters TC barrel redone by JDJ and turned into a 7x30 JDJ. New dies and the whole nine yards were required for the new chambering. It was supposed to be the greatest thing sense slice bread. I had to send the barrel back 3 times because it would not fire or chamber factory 7x30 waters rounds. After all the work and money spent, I got a massive increase in speed of 7 FPS over the factory rounds!

I cut my losses and sold everything.

Last edited by pullit; 06/22/20.

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Originally Posted by Mule Deer
Blacktail53,

You can, but whether it works correctly or not depends on how firmly the case neck holds the bullet, and how hard the firing pin whacks the primer. Generally find it much better to have the chamber correctly cut for a crush fit on new brass, or to neck up and then neck down again to get a crush fit.

These days, however, I find the easiest solution is to use a factory round that produces the desired ballistics. There are so many out there these days, especially those with steeper shoulders to begin with, that I really don't see any point in fooling with "improved" cases.



Thanks, John......and I whole heartedly agree.

I’m not convinced that there’s much reason to AI anything these days, unless you just want to...
Instead of chasing velocity to flatten trajectory, one can just spin a turret now days.
Of course there’s other reasons to go AI, if one wants.
I’ll spend the money on scopes and components instead.
But that’s just my take, and everyone is entitled to their own.....😎


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Originally Posted by Blacktail53
Originally Posted by Mule Deer
Blacktail53,

You can, but whether it works correctly or not depends on how firmly the case neck holds the bullet, and how hard the firing pin whacks the primer. Generally find it much better to have the chamber correctly cut for a crush fit on new brass, or to neck up and then neck down again to get a crush fit.

These days, however, I find the easiest solution is to use a factory round that produces the desired ballistics. There are so many out there these days, especially those with steeper shoulders to begin with, that I really don't see any point in fooling with "improved" cases.



Thanks, John......and I whole heartedly agree.

I’m not convinced that there’s much reason to AI anything these days, unless you just want to...
Instead of chasing velocity to flatten trajectory, one can just spin a turret now days.
Of course there’s other reasons to go AI, if one wants.
I’ll spend the money on scopes and components instead.
But that’s just my take, and everyone is entitled to their own.....😎




Less case trimming, but don't let that slow your roll.


The 7x30 Waters makes zero sense, since it headspaces on the rim.

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Originally Posted by Blacktail53
[quote=Mule Deer]Blacktail53,


Of course there’s other reasons to go AI, if one wants.




I was thinking case stretch, but with a 25° shoulder he's in good standing with most standard cartridges.


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Originally Posted by Mule Deer
Blacktail53,

You can, but whether it works correctly or not depends on how firmly the case neck holds the bullet, and how hard the firing pin whacks the primer. Generally find it much better to have the chamber correctly cut for a crush fit on new brass, or to neck up and then neck down again to get a crush fit.

These days, however, I find the easiest solution is to use a factory round that produces the desired ballistics. There are so many out there these days, especially those with steeper shoulders to begin with, that I really don't see any point in fooling with "improved" cases.


John
My thinking is that concerning rifles you forget very little and you probably forgot more about rifles in your sleep last night than I'll ever know. I highly respect your knowledge.

What I'm looking for is not necessarily what little I would gain velocity wise. The 6.5/284 would be a viable consideration. Or several others. I have a TC Custom Shop 26" barrel in 6.5X55. Loaded tight it will get to 3100 with 120 gr TTSX. It's fine as is. I'm looking to do some experimenting. I've had wildcats and AI rifles. Realizing not much is gained by going to Ai except maybe decreasing case stretch which the 6.5X55 is plenty capable of.
I'm looking at the hobby thing. I enjoy changing things, the puttering required to load for the AI, running the changed things across the chronograph, seeing how it touches the target and the satisfaction of using it on game. I'm looking at the hobby thing, thus the questions. What I have to gain is the FUN and challenges of doing it.
I greatly appreciate the input from all here. Sure is a pleasure to learn things. Also appreciate the PMs that came my way about this issue.
Thanks
Jim

Last edited by Rug3; 06/22/20.

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Socialism is a philosophy of failure,
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And a lot of the newer rounds have 30-35 degree shoulders.


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Hey John.!


I think it's great to finally have those newer cartridges with accompanying angles since we all know the earlier ones never worked on game or targets...especially the Swede.😁


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