338 Lapua mag improved or 338 Lapua mag AI?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by meatyrem, Jan 20, 2011.

  1. meatyrem

    meatyrem Well-Known Member

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    Of the two is there any difference? If so what is the difference? While reading other posts I'm seeing someone mention a 338 Lapua mag improved and also seeing a 338 Lapua mag AI mentioned. Are they one in the same? Also seeing an excaliber mentioned on a couple of different posts, I know it's a big boomer, I just am curious as to what case it uses and any modifications. The more I read about the 338 monsters the more I think I need one [ want one ]!

    Thanks for any info.
     
  2. BountyHunter

    BountyHunter Writers Guild

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    Pretty much the same, just wording. Generally those words are used interchangably.

    However, there are "variances" in the reamer specs for almost every version of an improved for AI chamber.

    You need to look carefully at the reamer specs and see what dies they match up with or your into custom dies.

    BH
     

  3. Long Time Long Ranger

    Long Time Long Ranger Well-Known Member

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    Many variations of the imp lapua. Some push the shoulder forward and many different shoulder angles and body taper. The AI is one of many versions and they are not interchangeable. Back when the Lapua case came out I was in contact with smiths all over the country as we tried different versions to find the best one. It seems like in the 90's every shop had there own proprietary version. Not a lot of difference performance wise with any of them with most getting 2900-3000 fps with a 300 smk out of a 30" barrel. The one I settled on had the shoulder pushed forward a few thousanths with minimum body taper and shot the 300 smk 2950-3000 fps out of a 28" barrel.

    The Excalibur is about the largest case out there over the counter with more capacity than the 338-416 Rigby case that was popular for years. It is the top performer with several grains more capacity than the 338-378 wby.
     
  4. jmden

    jmden Well-Known Member

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    My understanding of AI (Ackley Improved) is that it specifically designates a 40 degree shoulder. If I recall correctly, that was PO Ackley's 'trademark' shoulder angle. Many of the Lap Imps (and Imps in general today) are down around 35 degree shoulder angles.

    My 338 AX (Kirby Allens' Lap Imp) is doing 2980fps with 300 SMK over 102.0g Retumbo out of a 30" barrel, but I think I'm going to tone that down by at least .5 g here soon.
     
  5. Savvyup

    Savvyup Member

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    So if you just stick with a 338 lapua mag and go with a 1.25" diameter barrel with straight flutes for 30" in length you should be sitting good. Am I on the right track?
     
  6. Broz

    Broz Well-Known Member

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    That should get you 2825 to 2860 at 4000 ft with a 300 berger and H-1000. Pretty good platform if you ask me. I have 1500 rounds through my 338 LM with a 28" and it still shoots 1/2 moa to 1500 yards plus.

    Jeff
     
  7. Savvyup

    Savvyup Member

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    Thanks for the help. I was wondering if there was a magic length for a heavy hitting round to prevent the barrel whip. Or if it didn’t matter with a thick enough barrel.