.270 AM or 7mm AM

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by aitch, Oct 30, 2007.

  1. aitch

    aitch Well-Known Member

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    Here's an easy one. What's the difference between these two?

    If I'm correct, the bullet diameter of the former is .277" and the latter .284". Wouldn't think a .007 dia. difference would make much difference in performance all other things equal.
    I understand that the .270 AM is built on a 300 RUM necked down.
    The 7mm AM is a .338 Lapua necked down?

    What are the advantages of one over the other, disadvantages?
    I've read that the Lapua brass is superior.

    Thanks for helping a newby,
    Aitch
     
  2. J E Custom

    J E Custom Well-Known Member

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    The main difference is the choice of bullets.

    The 270 was always considered a hunting round therefore
    there were no match grade bullets for years.

    The 7mm on the other hand has been winning matches for a
    long time so match bullets are easy to find.

    Some bullet makers are starting to change that with some very
    good bullets, but there are still a lot more 7mm bullets,

    J E CUSTOM
     

  3. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Advantages for the 270 AM:

    EASY to form cases
    Brass is inexpensive
    Easy to fit into most conventional magnum length receivers(Rem 700)
    Very high performance for medium size game

    Disadvantages:
    Brass is not terribly strong with real high pressure loads
    Some say brass quality is not that great, I have never had a problem
    Very long, best with extended mag boxes, easy on the Rem 700
    Best bullets are custom bullets but many conventional bullets work

    Advantages for 7mm AM:
    Brass is extremely quality
    Brass is extremely strong
    Ability to use very heavy bullets for caliber, lots of bullet choices
    Very high performance, about the most ballistic performance you will get
    Relatively short compared to other true magnums

    Disadvantages:
    Brass is spendy if that is a concern
    More involved case forming for fireforming brass
    Need a receiver capable of handling the 338 Lapua size cases

    Thats about it.

    Comparing the two best loads of each, the 270 AM with the 169.5 gr ULD loaded to 3350 fps and the 7mm AM with the 200 gr ULD loaded to 3300 fps, the 7mm definately has an edge ballistically but they are both on the top rung for ballistic performance for medium size game such as that up to heavy deer.

    Kirby Allen(50)
     
  4. joecool

    joecool Well-Known Member

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    Kirby

    Don’t that gap close up between the two when the 270 AM is shooting 195s at around 3100 to 3200??? Looking at Exbal I don’t see that much of an advantage.

    I know if I have to mess around too much with brass!!! It will be 408 brass for me…

    Larry
     
  5. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Yes the 195 gr ULD RBBT will tighten up the spread a bit comparing the 270 AM with the 7mm AM but we have found some issues with the 195 gr pills in the 1-8 3 groove barrels designed for the 270 AM.

    Main thing is that the jackets on the 169.5 gr are much heavier then the J-4s used on the 195 so when the barrels get a bit of wear on them, they start to be pretty hard on these bullets, do not seem to have any problems with the heavier jacketed 169.5s however.

    As such, I recommend the 169.5s as the primary bullet for the 270 AM.

    That said, when they work, they are most impressive in that chambering.

    To be honest, when both are loaded to comfortable top end pressures for each case design, the 7mm AM will offer 100 fps more velocity then the 270 AM with that bullet weight class, not much but still 100 fps.

    Splitting hairs, just get one of either the 270 or 7mm and then a 338 AM for serious work!!! I am sure you would agree!!

    Kirby Allen(50)
     
  6. joecool

    joecool Well-Known Member

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    That’s a understatement!!!! Grins
     
  7. aitch

    aitch Well-Known Member

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  8. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Yes the Rem 700 can be set up to handle the Lapua, no, I do not recommend the Savage to be converted to the Lapua.

    Kirby Allen(50)
     
  9. Eaglet

    Eaglet Well-Known Member

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    Would you please explain?
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    I have found Savage receivers to be made of softer steel, or at least not heat treated as hard as Rem 700 receivers. As such, bolt lug support set back concerns me a great deal with the Savage and Lapua mix.

    I know Savage offered the short action Lazzeroni rounds for a very limited time. I wounder if there is a reason for the EXTREMELY limited time part????

    Just want to make sure things are safe for the long run.

    Kirby Allen(50)
     
  11. James Jones

    James Jones Well-Known Member

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    Kirby , how is your action desgine/building working out ??

    You get a good desgine it might be time to invest in some CNC tools or EDM ?

    I know that the CNC sure makes life alot easier when several on the same items have to be made. I have been making a few Suppressors lately and making the baffels on a manual lathe is a pain in the pee-pee especialy considering I'm machining Inconel 718 and Titanium !!

    My next build is gonna be on a custom action and I'm leaning twoard the 338 Lapua case as the parent either a 30 or 7mm of some sort , a 9lb 1000yd deer and elk rifle sounds very appealing
     
  12. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    James,

    The first production receiver should be here in the next week or so from what my manufacturer has told me. Do I believe it withthe delays I have already had........

    I designed the receiver and then submitted the design to a manufacturer with state of the art EDM and CNC machining capabilities. Looking over examples of some other receivers they have made showed quality on par with or better then Nesika Bay receivers so I am very hopeful.

    There have been alot of delays but with all the unique features I have designed into my Raptor receiver, this was to be expected to some degrees. Not just another Rem 700 clone so I expected some delays.

    Once we get everything tested and proven, then I will be ordering receivers by the 10 or 20 count lots which will drop cost some and also spead up shipping times.

    I would love to have the machines to do the work but the amount of $$ and time it would take to get set up and proficent with the machines is something I just cannot afford as far as time or money right now. It would be nice though.

    As far as your wildcats for elk at 1000 yards, you may want to look at the 30 cal as min for your choice. A big 7mm will certainly get the job done but at 1000 yards on heavy game, they are not overly authoritative on a rifle of this weight which will limit barrel length and mass.

    For deer, its perfect.

    My 9 lb 7mm AM is a joy to hunt with, that said, its a 1/2 mile rifle max from an accuracy and shootability standpoint.

    Kirby Allen(50)