Question for a gunsmith - 6.5 CM to .260 AI?

[omega1]

I find myself with an extra 6.5 Creedmoor barrel and was wondering if a .260 AI reamer would totally clean up the existing chamber?

 

[Dusty Stevens]

Gotta wonder what youd gain?

 

[hothead]

yes it would clean up. and you would be gaining +- 200fps

 

[Idaho-Lefty]

And don't overlook, the .260 SLR, ( 6.5 Super LR ) another,.. very, NICE round !
Basically a .260 with, a 30 degree shoulder, less Taper and,.. longer, Neck !
And,.. great Barrel, "Life" ! Can read about it at, 6mm AR home page.

 

[std7mag]

When your not hindered by magazine length, why would you want the CM?

 

[omega1]

Thanks for the feedback and especially for the information provided confirming the .260 AI reamer cleaning up the 6.5 CM chamber. I already have a .260 AI but it is way too heavy to carry as a hunting rifle, My intention is to have a hunting weight rifle with the performance of the .260 AI. A gain of 200 fps is significant to me.

 

[STOMP442]

The 260AI is everything the Creedmoor wishes it could be. Fantastic cartridge.

 

[Hohn]

The 260AI is everything the Creedmoor wishes it could be. Fantastic cartridge.

By what measure? Different cartridges developed for different constraints will produce different results. Horses for courses.

The 6.5 Creedmoor was specifically designed to optimize the balance between external ballistics and barrel life in a 2.8" OAL max.

The 260 AI is doing nothing for you if you don't load over 2.8" Which is fine. For single loading at longer lengths, the 260AI can absolutely beat a mag length Creedmoor.

But that's not what the 6.5 was intended for, and it is SIMPLY UNTRUE that the creedmoor "wishes" it could do that. At all.

But maybe Dave Emary was too dumb to know that he could improve performance by loading longer and going steeper on the shoulder. I bet not.

But keep telling yourself that alone have discovered the secret truth that has eluded the legions of people like me who ignorantly shoot and enjoy the 6.5 creed.

 

[Idaho-Lefty]

Since Omega1, is mainly using this Rifle for, Hunting ( see his, 2nd post ) 200 FPS more, is a BIG deal on Game and COAL is probably, NOT, a problem !

 

[STOMP442]

By what measure? Different cartridges developed for different constraints will produce different results. Horses for courses.

The 260 AI is doing nothing for you if you don't load over 2.8" Which is fine. .

I beg to differ. I have two .260 Ackleys both built on short actions with the same mag restrictions as the Creed and both are going 2950 plus fps while only using about a grain and a half more powder than the Creed. Accuracy is just as good, barrel life isn't an issue and you never have to trim it. It works fantastic on game as well.

 

[Hohn]

I beg to differ. I have two .260 Ackleys both built on short actions with the same mag restrictions as the Creed and both are going 2950 plus fps while only using about a grain and a half more powder than the Creed. Accuracy is just as good, barrel life isn't an issue and you never have to trim it. It works fantastic on game as well.

Not to be pedantic, but I didn't say "load to short action" I said "Load limit to 2.8" OAL." Those are different things. A 6.5 PRC is "loaded to short action." Perhaps you think that would be a fair comparison?


A comparison of load data is interesting context. Alliant data for a 140 speer:
260: 38.9gr RL16; 2663fps. 2.745" OAL
6.5cm: 42.24gr RL16; 2766fps. 2.76" OAL

Same bullets, same powder, nearly same OALs.

What if we just let each case run its preferred powder for max MV with that Speer SP?

260: 2731fps from 45.5gr of RL19
6.5 : 2802fps from 45.0gr of RL19 OALs as above.

More speed, less powder for the 6.5cm. The story plays out similarly with other 140gr bullets.

Alliant has no dog in a Rem/Hornady fight. This is not like citing Hornady data for the 6.5 (an obvious conflict of interest as they have incentive to water down the 260)

If you want to argue that the few grains of powder that AI adds to a 260 can transform it into a 6.5 PRC/SAUM-class cartridge, you go right ahead.

But the evidence says to me-- the base cartridges are so close in performance that the differences you observe are not due to any inherent superiority or advantage, but rather how far you are willing to push things.

In which case, bring on the 6.5 creedmoor guys running RL26 and getting crazy speed from long barrels with nuke hot one-and-done pressures and lets get this theater of the absurd rolling in earnest.

Not possible?

How about 2845 from a 22" compass at 2.8" OAL?

https://www.youtube.com/watch?v=i_HeFgF5BrM


I'm not saying the 260 is worse or better than 6.5. I'm saying they are essentially interchangeable in performance and AI-ing the 260 doesn't turn the 260 into something it wasn't. The claimed velocities you are getting are a measure of your risk tolerance and your particular use of it, not of the superior design of a 260ai case.


Best of luck to you.

 

[STOMP442]

Not to be pedantic, but I didn't say "load to short action" I said "Load limit to 2.8" OAL." Those are different things. A 6.5 PRC is "loaded to short action." Perhaps you think that would be a fair comparison?


A comparison of load data is interesting context. Alliant data for a 140 speer:
260: 38.9gr RL16; 2663fps. 2.745" OAL
6.5cm: 42.24gr RL16; 2766fps. 2.76" OAL

Same bullets, same powder, nearly same OALs.

What if we just let each case run its preferred powder for max MV with that Speer SP?

260: 2731fps from 45.5gr of RL19
6.5 : 2802fps from 45.0gr of RL19 OALs as above.

More speed, less powder for the 6.5cm. The story plays out similarly with other 140gr bullets.

Alliant has no dog in a Rem/Hornady fight. This is not like citing Hornady data for the 6.5 (an obvious conflict of interest as they have incentive to water down the 260)

If you want to argue that the few grains of powder that AI adds to a 260 can transform it into a 6.5 PRC/SAUM-class cartridge, you go right ahead.

But the evidence says to me-- the base cartridges are so close in performance that the differences you observe are not due to any inherent superiority or advantage, but rather how far you are willing to push things.

In which case, bring on the 6.5 creedmoor guys running RL26 and getting crazy speed from long barrels with nuke hot one-and-done pressures and lets get this theater of the absurd rolling in earnest.

Not possible?

How about 2845 from a 22" compass at 2.8" OAL?

https://www.youtube.com/watch?v=i_HeFgF5BrM


I'm not saying the 260 is worse or better than 6.5. I'm saying they are essentially interchangeable in performance and AI-ing the 260 doesn't turn the 260 into something it wasn't. The claimed velocities you are getting are a measure of your risk tolerance and your particular use of it, not of the superior design of a 260ai case.


Best of luck to you.

It's fairly obvious you have never loaded for or even shot a .260 AI. Anything the Creed does the 260 Ackley does better even at 2.800" its just that simple. Load the creed with 26 and do the same with the 260AI and watch it blow it doors off. I will argue until I am blue in the face on the fact that the .260 Ackley improved will in fact push a 140gr bullet easily to 2950 and even over 3000fps depending on powder used. I have nothing against the Creed, its a great cartridge, it is just far from the best 6.5 anything like so many seem to think.

 

[omega1]

It was never my intention to cause a debate on the virtues or short comings of any particular cartridge. I am a big 6.5 fan and I own, load for and shoot 6.5 Grendel, 6.5 Creedmoor, 260, 260AI, 6.5-284 and most recently 6.5 PRC. I think they all have their place and fill a particular roll very well otherwise I guess I wouldn't own them all. I just found myself with an extra 6.5 CM barrel and hoped I could turn it into a hunting weight .260AI with a minimum amount of effort and expense. Thanks for all the input, this site has a tremendous wealth of knowledge and experience and I am certainly not above taking advantage of it when I can.

 

[Hohn]

It's fairly obvious you have never loaded for or even shot a .260 AI. Anything the Creed does the 260 Ackley does better even at 2.800" its just that simple. Load the creed with 26 and do the same with the 260AI and watch it blow it doors off. I will argue until I am blue in the face on the fact that the .260 Ackley improved will in fact push a 140gr bullet easily to 2950 and even over 3000fps depending on powder used. I have nothing against the Creed, its a great cartridge, it is just far from the best 6.5 anything like so many seem to think.

I don’t think 6.5cm’s the best, and I don’t think I said so. I choose the creed over the .260 for one reason most: Remington SAAMI chambers all use the 3 degree throat and I wanted a modern 1.5 degree throat. I choose the 6.5 because in SAAMI form it’s a smarter reamer by my thinking. 30 degree shoulder, 1.5 degree throat, etc. If I wanted a SAAMI 6.5 for hunting only, I’d choose the .260. But I wanted mostly to shoot targets so I went creedmoor.

If I were building from a custom reamer, I might have chosen the .260. Or the AI version. I assume all the .260AI folks are revising the throat also.

Im glad you enjoy your AI. My 6.5 does everything exactly as I’d hoped it would. Except shoot 200-20x at 600...