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I think most go to the Ackley to increase the velocity. A friend wants to do it because he was told that the AI shoulder would give increased throat life.
Thoughts on this?

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I would be interested in this answer as well. If you gain 2% throat longevity it is clearly not worth it, for a 10% increase I would consider it questionably meaningful.

I have a 6mm Rem AI specifically to have longer lasting brass and save on throat wear. In my limited experience, I have seen 50 thou of throat erosion in about 400rounds. I would like to know if it would really be worse with a standard 6mm Rem. I am not loading hot or firing fast FWIW.

Thanks.


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I've had some smart ass answers on another forum. This guy is not trying to create a rocket ship, just a way to increase throat life. tcp, hopefully we will get some informed answers.

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Prolonged case life due to less stretching, yes. Throat life due to a change in shoulder angle, I don't know. I've read somewhere that rechambering a 243 to 243AI has been reported to reduce throat erosion, but I haven't done it and I haven't seen data that would support that scenario.

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I don't really see how it could Butch, if any difference it would be minute...


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The parent case the angle of the shoulder converges inside the neck so not like the 243 AI where you go from an outty to an inny This is supposed to reduce throat erosion.
People went to the Swede AI to gain barrel life over the 6.5x284 but when bullets where pushed to the same speed barrel life was also about the same.

I have always thought the 6.5x55 AI was about an ideal cartridge, but so is the standard Swede. Sort of like the 6.5x57 AAR. PO Ackley thought highly of this cartridge too.

Last edited by Tejano; 05/25/19.

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I rechambered a WIinchester/USRA 70 FWT from 6.5x55 to 6.5-284. While I got the expected bump in performance, in an exercise of 20/20 hindsight I regret that I did it.

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What's the definition/expectation of increased throat life ?


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The theory has always been that, if a line following the shoulder angle converges within the neck, there will be less erosion of the throat. I have never seen any data to support this and I strongly suspect it may be one of those things which we accept because it just makes sense. As has been pointed out though, the 6.5x55 is really OK in this regard. Lines following the shoulder angle converge within the neck. Throat erosion occurs just as you might expect it to in a cartridge the size of the 6,5x55. Barrels with 200 rounds through them look just fine to the naked eye but show some erosion with the borescope. I seriously doubt one would see any difference with the AI version. By the way, it seems as if a rifle with the long, tapered, standard throat, typical of European cartridges and , especially, the early Mausers, shows less erosion of the throat. Maybe because the throat starts life worn out!
As far as case life is concerned, any difference in stretching is simply due to a better fit between the dies and rifle chamber. In a strong, front-locking action, I have never observed any stretching of any case from firing. All elongation occurs during the sizing process. I've tested this in a 30/06, a 270, a 243, a 6ppc and a 6x47. If the cases were unsized, there was zero growth. In every case, the brass lengthened when it was full length sized. The closer the rifle chamber was to the die size, the less the case "stretched". AI cartridges usually had die and rifle chambers which were quite close dimensionally so they stretched less. I also believe the sharp shoulder does sort of help keep brass from stretching during sizing just because it doesn't flow around the corner as easily so the brass comes closer to getting put back to where it came from.
In a 6,5x55 with a custom chamber, one can size 2/3 of the neck before the body portion of the die contacts so the cases won't grow much. I use a .120" thick washer under the lock ring to size my 6.5x55 and then remove the washer if cases are starting to get tight. This works well because the case has enough taper that the body of the die doesn't do anything until the case is further in. GD

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I did the same (rechambering 6.5x55mm to 6.5-284Win) with a Ruger 77 Mk II years ago. Really a big mistake...

The round feeding was no longer "controlled" by any means, and the 22" factory barrel couldn't come anywhere near taking advantage of the 6.5-284 potential.

I've just recently been looking to resurrect that rifle. Since I'm forced to re-barrel now, I'm looking at a heavier, longer barrel. Question is chambering. I found a 6.5 Wolf Killer (wildcat) on a forum, and that looks to be exactly what I want. Problem is, getting it done. There's the 6.5x55mm Ackley out there, but I can't say I love the 40° shoulder angle.

I wanted to go the full wildcat route to show my son how it all works, but the hassle-factor is rearing its ugly head. I did a full-blown wildcat back 30 years ago, when the hassle-factor was practically a plus. Now, I just want to get it done, so I have a usable rifle, again.

Last edited by pjk81; 01/27/24. Reason: expanded by author
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The magic angle is closer to 30⁰, not 40⁰


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Increase throat life huh? What do you think you'd get with a standard 6.5x55? You plan on shooting that many rounds from it in your life. I believe the only real value to any Al cartridge is an ego trip. You get to tell your friends you got an AI! I seem to recall reading that even Ackly felt the AI's had little to offer of real value!

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Ackley spoke highly of the 7x57AI and as well of the various 6.5AIs. I would think a 6.55x55AI would work quite well. I have a 7x57AI and it works "as advertised". As far as throat life, only time/rounds will tell.


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Originally Posted by pjk81
I did the same (rechambering 6.5x55mm to 6.5-284Win) with a Ruger 77 Mk II years ago. Really a big mistake...

The round feeding was no longer "controlled" by any means, and the 22" factory barrel couldn't come anywhere near taking advantage of the 6.5-284 potential.

I've just recently been looking to resurrect that rifle. Since I'm forced to re-barrel now, I'm looking at a heavier, longer barrel. Question is chambering. I found a 6.5 Wolf Killer (wildcat) on a forum, and that looks to be exactly what I want. Problem is, getting it done. There's the 6.5x55mm Ackley out there, but I can't say I love the 40° shoulder angle.

I wanted to go the full wildcat route to show my son how it all works, but the hassle-factor is rearing its ugly head. I did a full-blown wildcat back 30 years ago, when the hassle-factor was practically a plus. Now, I just want to get it done, so I have a usable rifle, again.

If you're worried about feeding, then rebarreling to an Ackley Improved case isn't the answer. A regular 6.5x55 loaded to modern pressures will do anything you'll need from the rifle.

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I think that throat erosion has to do with heat and pressure. Not changing the geometry of a case.


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I picked up a Husqvarna 3000 in 6.5x55. First time I pulled the trigger, I got a blast of gas and primer fragments. Safety glasses work!! It seems it had been rechambered to 6.5-284 and never re stamped. I haven't played with it much, but it does have a feeding issue. I hope I can go back to x55, but I don't know if I will be able to get it to feed at all.


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Originally Posted by Cowboybart
I picked up a Husqvarna 3000 in 6.5x55. First time I pulled the trigger, I got a blast of gas and primer fragments. Safety glasses work!! It seems it had been rechambered to 6.5-284 and never re stamped. I haven't played with it much, but it does have a feeding issue. I hope I can go back to x55, but I don't know if I will be able to get it to feed at all.

Post pics of the feed rails. If they haven't been massaged, a rebarrel should fix your problem. Otherwise, Dave can make anything feed, just ask him.

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Man at this point in my life I’d love to shoot enough that throat life was a concern.

Sounds like a dream!

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I’ve been shooting a 6.5 Addiction for several years and it’s been a great cartridge. Very efficient and seems to give good barrel life, I had almost 2000 rounds on a barrel and it was still going. Mine is in a short action so the bullets are pretty deep in the case, 51gr of RL 26 is good for around 3100 in a 26” barrel. For the loading the longer bullets out a medium length action like the Defiance XM would be the way to go.
The addiction has a 37* shoulder with a little more taper than the true AI, lots of info online about it. Very similar to the 6.5 GWI and 6.5 BJAI.

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Throat errosion is a product of heat and unburnt powder wear. The 6.5x55 is a well balances cartridge as is. Sugges your frieind can the SAAMI data and go to CIP data, which is more realistic, if he wants more velocity. but throat extortion is what it is and no AI 40 degree shoulder is going to make one bit of difference to X pressure at 27 degrees and the very same X pressure at 40 degrees.

The start load for an Ackley is normally a max load for the non Ackley version, does not mean one thing if the two pressures are exactly the same. Any advantage is made a mute point by more powder capacity

Last edited by Rapier; 02/12/24.

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