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260rem vs 260rem AI

Discussion in 'Rifle Country' started by taliv, Mar 25, 2010.

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  1. taliv

    taliv Moderator

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    anyone have any experience Ackley Improving this cartridge?

    I see 260 AI dies for sale, but don't know anyone who uses it.

    Does the change in shoulder angle inhibit feeding in a bolt gun at all?

    how much speed increase did you get? what weight bullets you using?
     
  2. MCMXI

    MCMXI Member

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    From Zak's article here ...

    "My friend Chuck was seduced by the ballistics of 6.5-284 Norma but wanted to stay with a real short-action cartridge. The solution was 6.5-08 Ackley Improved, which is a .260 case blown out to have a steeper shoulder angle and less body taper. The benefit of the extra case capacity is an additional 80 to 120 fps, however, cases must be fire-formed which takes time and eats away additional barrel life. Since the Ackley Improved version is more overbore, it will burn out barrels faster than .260 Remington. The straight walls of the Ackley Improved also do not work well in double-stack double-feed magazines, such as those for the AI-AW and AR-10. Chuck's rifle was built by TJ's gunsmithing in Aurora, Colorado around a Surgeon Tactical action, with a 26-inch Krieger #10 MTU-contour barrel. Its McMillan A5 stock was fitted with the Badger AICS detachable box magazine system. A US Optics 3.2-17x44 mm SN3 scope is mounted on USO rings directly to the Surgeon receiver. In fire-formed brass, Chuck's load shoots the 142 Sierra MatchKing at 2900 fps using H4831SC powder. Everyone who shoots this rifle compares it to a laser beam."

    I just ordered a .260 Rem Krieger barrel this morning for a new build. I thought about the .260 AI but after reading Zak's article (and asking him questions via PM) I decided that the .260 was the way to go. Now I need to order dies, brass and bullets!!

    :)
     
  3. Zak Smith

    Zak Smith Moderator Emeritus

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    Thanks. Since I wrote that Reloder 17 "happened" and we're all shooting the regular .260 Rem at 2900-3000 fps with the 139's. Even before that, I didn't think the extra effort of the "AI" version was worth it. Chuck replaced his first .260AI barrel at just under 3000 rounds. It was shooting 3/4 MOA at that time.

    -z
     
  4. MCMXI

    MCMXI Member

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    The obvious question here is ... with what? Another .260 AI or did he revert to a .260 Rem? I'm not sure if when you say "we're all shooting the regular .260 Rem at 2900-3000 fps with the 139's" you're including Chuck in that statement.

    But thanks for getting me on the .260 Rem bandwagon.

    :)
     
  5. R.W.Dale

    R.W.Dale Member

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    IME you do not get any speed increase directly from the case capacity increase. What you do get with an "ackley" is a more stable case shape that masks pressure signs and thus convinces you to load to higher pressures.

    Not to say this is a bad thing as anytime you're changing case shape to a design that masks pressure signs you're typically working with less case stretch and brass flow and therefore longer case life
     
  6. Zak Smith

    Zak Smith Moderator Emeritus

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    Sorry, I did not mean to include him in that "we". He bought two barrels and the .260AI reamer when he had the rifle built, so he's going to stick with the Ackley for the second barrel. I don't know his plans after that one's toast (which will probably be in early 2012).

    Based on where I could load H4831SC and where he's loading it in the Ackley, I think you can simply put more powder in the AI case and not have as high a pressure spike.

    I do not agree that the AI case only gives velocity increase because of case shape-- it may be partly that, but I believe the dominant reason is increase in case capacity. Chuck can simply fit more H4831SC in the AI case than I can in .260REM. Also, if you look at cartridge pairs that have a little more water capacity difference than .260 vs .260AI, say 6.5x47 vs. .260REM, the 6.5x47 has a velocity disadvantage when loaded to the same pressure because it has less case capacity.

    For my application in the AI-AW, I don't think the AI cases would have fed right from the double-feed AW mags. They work fine from the single-feed AICS mags, though.
     
  7. taliv

    taliv Moderator

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    have he tried reloader 17 in the AI case? maybe even more velocity?

    how much of a disadvantage is the single-feed aics mags vs aiaw mags in the matches you shoot?
     
  8. pdd614

    pdd614 Member

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    no disadvantage to the aics mag, except maybe its longer in length and has a shorter c.o.a.l. The aw rifle will not shoot the aics mags and vis versa. You have to modify a rem 700 or clone to run the aw mags. Both hold ten rounds, and both do the job well. The aw is slightly cheaper though.
     
  9. Zak Smith

    Zak Smith Moderator Emeritus

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    I don't think he has tried it yet. I bet you'd get even more velocity, probably break 3000 fps in the AI case. Taking 3050 fps vs 2900 fps (my load now), at 1200 yards the 3050 would have 6" less wind (10 mph cross) and would be about a mil flatter. At some point it comes down to just how much barrel life you want.

    Since there are 10-round AICS mags available, the only practical difference is those stick out further from the action than 10-round AW mags. It's a moot point since most people don't pick a bolt action/rifle based on a very small difference in magazine design.

    -z
     
  10. berettashotgun

    berettashotgun Member

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    I cannot remember where I read it - but, I THINK I remember something about the "break even" point of deciding to go AI on a chamber was a percentage increase. His break even point will possibly be different from others.
    I just cannot seem to remember the percent that Mr. Ackley stated.
    Has anyone used any 4007 in one of the 260's?
    I'm thinking of trying it on a few work up loads for a 6.5x55 Steyr with 130 VLD's. Just for hunting as the data I have appears to dictate lighter bullets work better with 4007.
     
  11. Clipper

    Clipper Member

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    I have a .257 Roberts AI, and what I like about it is the fact I can shoot my preferred +P factory loads as I fireform brass, and the straighter case wall reduces bolt pressure. I intend to duplicate factory Roberts +P loads in the reloaded cases...BTW, I bought the rifle used (FN Mauser custom) and pretty much stole it because the AI chamber scared off a lot of potential buyers. Of course I could squeeze a bit more performance from it, but I prefer to duplicate an accurate factory load in case I need to buy ammo on a hunt.
     
  12. USSR

    USSR Member

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    I did the "6.5 case debate" about 8 years ago, and settled on the 6.5x55. Readily available quality brass (Lapua), and the ability to run the 139-142gr match bullets at 2950fps. Have never regretted my choice.

    Don
     
  13. NCsmitty

    NCsmitty Member

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    I faced a decision of 6.5 calibers much like others, and poured over ballistic tables and cartridge designs, and came to the conclusion that the 110 year old 6.5x55 is an amazingly well designed case.
    Along with a 3gr powder advantage over the 260, the deciding factor was the longer, more supportive neck. IMO, that short neck of the family of 308 based cartridges is a draw back, and yes, I know that many people shoot competitively with that short neck, but they should admit that in some rifles their bullets intrude into the powder space, inhibiting performance.
    I do not shoot competition nor plan on doing that, but do like to do impromptu shooting for group and testing of different powder and bullet combinations.



    NCsmitty
     
  14. Maverick223

    Maverick223 Member

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    For a reloader I don't see any good reason to not go with the AI cartridge. You can still shoot standard cartridges in a pinch, you can fireform with a few grains of pistol powder and a patch from a T-shirt, and if you decide you want it have a decent velocity gain. If you don't have the strong urge to burn up your barrel, you can always shoot a reduced load that affords better case life.

    :)
     
  15. Zak Smith

    Zak Smith Moderator Emeritus

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    A lot of people get hung up on the bottom of the bullet being below the neck or below the shoulder when seated. This by itself doesn't really matter, other than it reduces the usable powder volume in that cartridge. Some people try to "fix" this by going to a cartridge with a shorter body but keeping the bullet seated to a long OAL (eg, some posted arguments "for" 6.5x47 or 6.5CM over .260). This does not yield additional velocity performance because the of case loses usable volume with the shorter body. What matters is the usable powder volume with the bullet seated to the desired OAL. The 6.5x55 does have more volume- no arguing that
     
  16. Dr. Tad Hussein Winslow

    Dr. Tad Hussein Winslow member

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    The original .260 AI became popularized in 1894 - it's called the 6.5x55mm swedish. Lot easier to get brass for too! :D I know, I'm of very little to no help. :p
     
  17. Maverick223

    Maverick223 Member

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    I believe that the reason for this is the belief that the projectile must be pushed with the powder behind it, rather than the pressure popping it out like a dent in a soda can. There is no substitute for case capacity.

    :)
     
  18. Ol` Joe

    Ol` Joe Member

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    It`s been pretty well shown a AI cartridge built on a straight walled bottleneck case like the 308 or 223 doesn`t gain much velocity if all else is equal (pressure, barrel lgt, ect). The gain in capacity just isn`t enough to make it worth while.
    John Barsness has a 4 to 1 rule he uses to figure velocity gain due to increase in powder charge. You can find out about it here.
    http://findarticles.com/p/articles/mi_m0BQY/is_4_55/ai_n31392893/
     
  19. rangerruck

    rangerruck Member

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    you could go this route as well, but I don't have any idea of bbl burn with this;
    supposedly better b.c.'s than the 260's or 6.5's...
    http://www.6mmbr.com/243Win.html

    go down about 3 paragraphs where it talks about match bullets.
     
  20. Zak Smith

    Zak Smith Moderator Emeritus

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    Their BCs do not match the 140gr class in 6.5 but the 243 makes it up
    with velocity. Barrel life approx 1/2 of 260
     
  21. rangerruck

    rangerruck Member

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    WOW!!!! half the life!!!! I change my mind then; do something in 6.5- maybe a nice , mild grendel!
     
  22. rsilvers

    rsilvers Member

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    6.5x55 is about 46,000 psi.

    .260 is about 60,000 psi.

    6.5x55 does not work in a short action, does not use a .308 bolt face, and can not share .308 mags. Those are all things to consider for some platforms.

    AI is rebarreling my AWP for .260 and I will see what it can do. 42.5 grains of RE-17 in Rem brass with Rem primer loaded to max OAL with a 139 Scenar is a max load.
     
  23. USSR

    USSR Member

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    That is SAAMI pressure levels for the 6.5x55 ONLY because there are still single-lug Norwegian Krags out there. Once you move to a modern receiver and handload, the 6.5x55 enjoys the same 60,000 psi pressure level of the .260, and it's greater case capacity allows for about 100fps more velocity.

    Don
     
  24. rsilvers

    rsilvers Member

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    Yes I know, but one still cannot load over SAAMI pressure for it and sell it commercially while being SAAMI legal. So it becomes a handload-only situation.
     
  25. Maverick223

    Maverick223 Member

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    I don't believe this is a problem for the average 6.5mm/.260cal shooter as the factory ammunition offerings are sparse, especially WRT match grade cartridges.

    :)
     
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