ackley improvement

Discussion in 'Large-Bore/Small-Bore Rifle/Shotgun' started by 68c15, Aug 17, 2012.

  1. 68c15

    68c15 Well-Known Member Supporting Member

    Nov 22, 2011
    I have heard this term a few times. what is it and how does a guy do it?
  2. hardluk1

    hardluk1 Member

    Nov 15, 2011
    nc mountains
    I know that for the average hunter its not worth the cost. But it will give you an extra 100fps or more. If your a seasoned reloader and have fine shooting rifle as is then It would be worth while to you. Read here -
    Last edited: Aug 17, 2012

  3. Bindernut

    Bindernut Well-Known Member

    Oct 24, 2007
    ND, USA
    The late, great P.O. Ackley was one of the most prolific wildcatters of the 20th century. He made an Ackley Improved version of most of the current factory cartridge of the period plus a bunch of other cartridges as well.

    His basic recipe for the common Ackley Improved version was to blow the case walls out so they're nearly straight and change the shoulder angle to an even 40°.
    The measurement from the datum line on the neck to the head remains unchanged (or set back just slightly) so that the parent case is properly headspaced. This way you can still fire the parent cartridge in the Ackley chamber to fireform it...or if you run out of AI ammo while away from home on a hunting trip.
    You get a little extra case capacity with the AI version, the exact reasoning behind it is always debated. Some say he did it to squeeze more velocity out of the case, but others say the changes are made for a more stable cartridge case (which is how I understand his writings).

    Even if Ackley himself didn't develop it, someone doing a straighter-walled, 40°-shoulder improved version of a cartridge will almost always label it an Ackley Improved version because it follows his system.

    Here are a couple of scans from the Sierra manual of the .257 Roberts and it's AI version. If you compare the dimensions you can see basically what's all been done.

    Some time, you can rechamber to the AI version of a cartridge simply by recutting the chamber with the AI reamer, but most of the time you also need to set the barrel back a few thousands so that you get a clean cut and can set the proper headspace.
    I know several guys who've gotten AI jobs done but the chamber was cut too long to properly headspace the parent case afterwards. Not a big deal if you're a handloader and you're aware of it when fireforming cases, but it can catch you off guard though too.

    Even if you're not a wildcatter or reloader, Ackley's Handbook for Shooters & Reloaders (a 2-vol set) is still must-have reading material. If you ever find a copy, check it out.

    Attached Files:

    Last edited: Aug 17, 2012
  4. Bindernut

    Bindernut Well-Known Member

    Oct 24, 2007
    ND, USA
    I hope that 1000fos is a typo hardluk. ;)
    I only got an extra 100-150fps out of the .22-6mm 30°-shoulder that I had a few years back. :D
  5. cpttango30

    cpttango30 Guest

    That is because you are at the point of diminishing returns. You are so overboar with that cartridge to begin with that just changing the shoulder isn't going to give you much improvement.

    22-6mm is one of the more wasteful cartridges out there. It burns way more powder than is needed to reach velocities that do nothing but erode the throat and barrel.
  6. Bindernut

    Bindernut Well-Known Member

    Oct 24, 2007
    ND, USA
    You missed my point tango. I was ribbing hardluk about his 1000fps typo. :)
    150fps or so is the approximate velocity gain you'll see out of any of the AI versions. Not bad considering he didn't develop those wildcats for the velocity gain.

    And getting off track, but the 22-6mm isn't a barrel burner unless you load it that way. Same as a 22-250 or a Swift.
    Last edited: Aug 17, 2012
  7. hardluk1

    hardluk1 Member

    Nov 15, 2011
    nc mountains
    Bindernut , thanks for catching that.
  8. polishshooter

    polishshooter Well-Known Member

    Mar 25, 2001
    Funny the timing of this;)

    My buddies that I shoot prairie dogs with both shoot custom .22-250s and .223s, and the first year I went with them I confessed over the nightly drinks that I always wanted a .220 Swift, and one of them said "now you have a reason to buy one,"

    I always like to be different, so the second year I show up with my Ruger M77VT in .220 Swift, and popped quite a few dogs but it wasn't impressive enough with the Tasco "World Class" on it.:cool:

    This year I showed up with a Leupold M8 12x on it and it stole the some sage on here so aptly put it when I was contemplating buying the Swift...."The .220 Swift does BAD things to Prairie Dogs..." (ESPECIALLY 50 gr Vmax's at somewhere between 4000-4100...):D:D:D

    Both of them this year shot it enough and blew up enough dogs that when they got up from the bench I heard from both of them the mumbled...."Nice Rifle....";):D:D

    Well, this year after a day of shooting, after the rifles were cleaned, and we were sitting around outside the motel smoking good cigars and drinking good scotch and bourbon, the same buddy who talked me into buying a Swift 3 years ago, after a contemplative moment (and his third or fourth single malt;)) suddenly says to us....

    "...I think I am going to have the M700 (.22-250) bored out to Ackley Improved...."

    My other buddy asks him "Why?"

    Jim said..." I'm getting sick of hearing Mike brag about that #@$Q%%@! '4000fps' so much....":p:p:p

    Considering he had his Hornet bored out to K- and he had ammo and loads he worked up for it this year and it did really well out to almost 200 offhand and from a walking stick bipod this year, I would not put it past him to have it done for next year, AND bring his chronograph with him to the Prairie...

    (Of course, I also got in my fair share of ".22-250s are for wimps that can't handle the REAL man's varmint gun, the SWIFT" which probably got his goat TOO:cool:;):D:D:D:D)

    Next year I plan to have a decent .222 with good loads with me so I can diss their .223s :D:D:D:D;):p

    But don't worry, we all are "Equal Opportunity Abusers...." They get their shots in as well...;)
    Last edited: Aug 17, 2012
  9. JLA

    JLA Well-Known Member

    Feb 26, 2007
    Heart Of Texas
    I say if you handload, by all means AI. If you do not it will benefit you to stick with the std. chamber..
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