260 in a 6.5cm chamber?

[highdrum]

I might have to see if I can find a takeoff for cheap and give it a try...

If it isn't SAAMI then isn't it by definition a 'wildcat'? ... even if using a SAAMI reamer, as soon as it is taken deeper it is no longer SAAMI right?

Just my thoughts on this - appreciate you have challenged me to think/rethink about and through it ...

- a special die for full length sizing will be required if the chamber is deeper than the SAAMI in order to shrink the body near the base as it grows over time
- other 'wildcat' cartridges (i.e. 260 rem AI) can often use standard dies except for body or full length (i.e. Lee 260 collet neck and seater for 260 AI) ... design and function of the die will drive this
- 30 vs 40 degree shoulder for improved feeding is arguable but I do agree the 'potential' exists for improved feeding with 30 vs 40 ... there is also a 260 Improved 30 deg shoulder and if not mistaken also a 35 ... and all the above applies to them as well.

Since the creedmoor case was created off the shorter 30TC case (as compared to 308) in order to have the advantages of the shorter case and subsequent ability to seat the long bullets without intruding into/reducing the case capacity, it doesn't make sense to me to try and "revert" the length back to the 308 case length ... unless you just want to experiment with a wildcat. No judgement from me on that - my 6.5 ackley (wildcat) and 6BR (former wildcat) rifles are my favorites for the range ... And all the above being said - I'm curious who is doing it, to what success, what kinds of muzzle velocity and accuracy is being achieved, etc, etc ...

Cheers

I've had multiple conversations with a few guys actually shooting the "creed ultra" chamber, they're using standard creed dies. Just leaving basically 0.120" of the case being not sized by the die. I'd have my smith polish out another 2 thou at the 200 line just so I don't get clickers. There are some die manufacturers coming to the table with dies that size more at the web area by design as brass has come a long way and case heads are lasting longer than the work hardening of the sidewalls. I sent a message to the smith to see if he'd ream a factory barrel as I found a Tikka 6.5cm take off for 80$

 

[MNbogboy]

Back in "BC", Before Creedmoor, years, we called this a 260AI, and it was available in 30 and 40 degree shoulders. Hmmm, now that I think about it, I think I will rename and reintroduce my 260AI's as the 6.5"CMM", CM Magnum. It should sell like hotcakes! When at the range and people ask what caliber I am shooting, I can be all modern and cool with my "new" 6.5CMM.....

Seems that several are playing with this one. Ive run the reamer in approx. .080 deeper in the CM. 260, 7-08 or even 08 brass cleans up the shoulder to 30° in the CM die. Trim to 2.004, while maintaining CM neck length. After one fireform for body diameter the capacity increases approx. 2-1/2 grains. CM die works fine.

Done this on three barrels, a shilen 26", a shaw 19", & a stock savage 22". With limited testing with only h4350 & h4831sc it definitely shows an advantage of reaching original CM nodes in a variety of bullets with less pressure.
Other advantages are obviously a "no problem" wildcat with no special reamer, dies or fireforming.

Btw: named mine 260 CML (creedmoor long)...lol

 

[nkyshooter]

True ... "different" ... at nuance level with the point being it is a solution to a problem that was solved many many years ago in the 260 AI and therefore does not exist.

However - from the perspective of learning and wildcatting, there is value and I think we all benefit from learning more, even when we are re-inventing a wheel or in some cases such as this one, 'regressing' back to what were trying to improve upon in the first place ...

 

[Deleted member 115654]

6.5x55 by any other name ? 6.5x55 AI would blow it away. Then there's the 6.5 PRC -----

 

[MNbogboy]

True ... "different" ... at nuance level with the point being it is a solution to a problem that was solved many many years ago in the 260 AI and therefore does not exist.

However - from the perspective of learning and wildcatting, there is value and I think we all benefit from learning more, even when we are re-inventing a wheel or in some cases such as this one, 'regressing' back to what were trying to improve upon in the first place ...

The 260 Super the 30° shouder version of the 260 still had the short neck & required fireforming to form the shoulder as does the 260 AI 40°. So advantages of a pre-shouldered case where full "bump" can be set before any firing takes place definitely has advantage by minimizing initial case stretch and possibly extending ultimate case life.

 

[highdrum]

The 260 Super the 30° shouder version of the 260 still had the short neck & required fireforming to form the shoulder as does the 260 AI 40°. So advantages of a pre-shouldered case where full "bump" can be set before any firing takes place definitely has advantage by minimizing initial case stretch and possibly extending ultimate case life.

So let me get this straight, you chamber a 6.5cm reamer 80k deep, and bump 260 brass back about 25k with a creed die to where it chambers and call it good? It still sounds like you're gonna be forming them to a point. So might as well just push the creed deep enough to close on a 260 gauge and be done. Get the most of the capacity? I like the long neck of the creedmoor. Maybe I should just do a minimal taper 30° 6.5x55 and be done.

 

[MNbogboy]

So let me get this straight, you chamber a 6.5cm reamer 80k deep, and bump 260 brass back about 25k with a creed die to where it chambers and call it good? It still sounds like you're gonna be forming them to a point. So might as well just push the creed deep enough to close on a 260 gauge and be done. Get the most of the capacity? I like the long neck of the creedmoor. Maybe I should just do a minimal taper 30° 6.5x55 and be done.

You are correct. I believe there is an advantage however that the fireforming is limited to the slight body diameter difference therefor minimizing the amount of brass stretching. The initial cases fresh out of the die almost look exactly like fireformed.
A disadvantage not mentioned was they do require a substantial initial trimming.
I did consider running the reamer in as you mentioned but opted for the shorter version to help maintain the diameter at rear of the chamber (even though the number is miniscule).
Dont read me wrong there is nothing wrong with the 260 AI 40° or the 260 Super (30°). If i had either one of those reamers i would definitely wouldnt be afraid of either. I do have a 6.5/257 A.I. 40° reamer and have done several chambers with it. It is my go-to deer caliber.

 

[highdrum]

You are correct. I believe there is an advantage however that the fireforming is limited to the slight body diameter difference therefor minimizing the amount of brass stretching. The initial cases fresh out of the die almost look exactly like fireformed.
A disadvantage not mentioned was they do require a substantial initial trimming.
I did consider running the reamer in as you mentioned but opted for the shorter version to help maintain the diameter at rear of the chamber (even though the number is miniscule).
Dont read me wrong there is nothing wrong with the 260 AI 40° or the 260 Super (30°). If i had either one of those reamers i would definitely wouldnt be afraid of either. I do have a 6.5/257 A.I. 40° reamer and have done several chambers with it. It is my go-to deer caliber.

I've always wanted an improved sweede. I do like the x57 case better but finding quality brass is difficult.

 

[MNbogboy]

I've always wanted an improved sweede. I do like the x57 case better but finding quality brass is difficult.

Thinking the improved swede would be great also. Was shy to build one because of brass options. Although Lapua makes brass for it. You cant make it from any other caliber like x57 brass.
Most of the 57 brass for my Ackleys was made from 06 & 270 brass. I also chambered several 257 Bob Ackleys. Most 7x57 brass and Roberts brass (when you could find it) would end up short or "real" short after fireforming to 40°. Thus making it from the longer stuff would always get you where you wanted to be with full length necks.
Thats another diadvantage to the 260 A.I. where some short length brass would leave you with shorter necks than the already short 260 neck. The 40° Ackley is known for not growing much so they may end up short for life.

 

[birdiemc]

However - from the perspective of learning and wildcatting, there is value and I think we all benefit from learning more, even when we are re-inventing a wheel or in some cases such as this one, 'regressing' back to what were trying to improve upon in the first place ...

Kinda seems like a good way to stick just your toe in to the wildcatting waters. Might not necessarily be inventing anything new or improved but it sure makes it easy to try.

 

[J E Custom]

This comment popped up in the latest manbun thread and got a little attention, but then passed over...but it interested me. If I understand correctly, the 30degree shoulder is what all the hype is about in the creedmore package so this seems like a cool idea...but I know nothing at all about wildcatting (I suppose would be the best term) so what's the deal, would cutting the chamber deeper with 6.5cm reamer then running fireformed 260rem brass have a true advantage?

The right Gunsmith might pull this off, but I would never use a different reamer than the one made for the cartridge you want. If you want something different than the SAMMI chambering, I would recommend buying a special reamer with the changes you want in it.

Combining to different reamers/chambers is risky in my opinion and could turnout badly. The Creedmoor has some other differences that could effect all load data and performance of a 260 and the idea of a 260 AI would solve all of these differences.

Maybe I'm to cautious But when you spend all the money to build a quality/accurate rifle, the cost of a reamer is minuscule.

Just My opinion

J E CUSTOM

 

[sturner]

6.5 creed on left
260 middle
260 AI on right

 

[Kiwi Greg]

I built a long 6.5 CM a few years ago now,
I took the extra over all length left in the AI 10 shot double stack mag with the 147 ELDM & got the reamer run in deeper
Then took some Lapua 308 Palmer brass sized, trimmed & neck turned to suit
It went very well with a healthy dose of RL16

 

[highdrum]

I built a long 6.5 CM a few years ago now,
I took the extra over all length left in the AI 10 shot double stack mag with the 147 ELDM & got the reamer run in deeper
Then took some Lapua 308 Palmer brass sized, trimmed & neck turned to suit
It went very well with a healthy dose of RL16

Coukd you have gone deeper? I see that the aics mag was your limit. I have a tikka long action so coal is of zero concern.