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.270 AM or 7mm AM

 
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  #1  
Old 10-30-2007, 02:45 PM
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.270 AM or 7mm AM

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
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  #2  
Old 10-30-2007, 07:04 PM
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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
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  #3  
Old 10-31-2007, 11:08 AM
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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)
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Kirby Allen(50)

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  #4  
Old 10-31-2007, 11:46 AM
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Kirby

Donít that gap close up between the two when the 270 AM is shooting 195s at around 3100 to 3200??? Looking at Exbal I donít see that much of an advantage.

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

Larry
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  #5  
Old 10-31-2007, 01:18 PM
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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)
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  #6  
Old 10-31-2007, 05:59 PM
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Quote:
Originally Posted by Fiftydriver View Post

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)
Thatís a understatement!!!! Grins
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  #7  
Old 11-01-2007, 03:35 PM
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[quote=Fiftydriver;171074]Advantages for the 270 AM:

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


Kirby,

I'm assuming the Rem 700 will handle the 338 Lapua size case.
How about the Savage 111, 112?

Thanks,
Aitch
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