7mm w/ 180 Berger 3300FPS possible?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by 30-338, Feb 23, 2010.

  1. 30-338

    30-338 Well-Known Member

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    Hi Brothers... I am dreaming of a 7mm rifle with a 30 inch barrel that can accurately shoot the 180 Bergers at a genuine 3300 FPS. I have talked with several 7RUM shooters that claim this speed but it seems unrealistic to me???? Ken Lemas' post and his 7/338 Norma 35 degree shoulder is promising but not quite there. I have been researching the 7/338 Lapua Improved which seems like a viable option. I want to stay in the Remy 700 length action. Is this feasible??? Any opinions/help would be appreciated Thanks in advance 30-338
     
  2. JeffVN

    JeffVN Well-Known Member

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    I've got a 7/338 Norma Mag being built right now - actually long overdue but that is a different story. If you put a long enough barrel on them 3,300 seems like its easily in reach...especailly at any altitude at all.

    As for teh 7mm Berger 180s hldoing together at 3,300 fps, I think the original ones (thin jackets also now called hunting) have no chance of doing it; the new thick jackets (also called target) may or they may not....3,300 is pretty spicy, and approximatley where the various jacketed 338s start to tear themselves apart (at least the Sierra do from what I've been told).

    I did talk with Bob Cauterucio about his 189 grain 7mm (purported bc of .725+) and he said his will do close to 3,300 fps. He uses a thicker jacket for his than Berger used to use. How they hold up when compared with the newer Target Berger's I do not know. But i will when my rifle gets delivered, as i have 2,000 of Bob's 189s and several thouseand of teh Berger 180s (I use them in my7WSM F-CLass rig)

    JeffVN
     

  3. 30-338

    30-338 Well-Known Member

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    Thanks for the thoughtful response Jeff. So it seems like the Berger thicks MAY do it??? And the Cauterucio 189's probably will do it? Perhaps I am on a fool's errand. Bob C lives close to me so I will talk to him. I guess Len shot his bullets for quite a while although I have heard that Bob is a little optimistic re: BC...don't really know...just heard that...I hope you get your 7/338 Norma soon. Ken Lemas is doing some interesting things right now with that cartridge...he is going to neck one down to .284 and use a 35 degree shoulder. Then neck one down to 30 caliber and finally do a .338. He will be doing testing with the 180 Bergers tomorrow in Idaho, weather permitting.....Thank you 30-338
     
  4. Too Tall Rosenwald

    Too Tall Rosenwald Well-Known Member

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    Jeff is Chris building that rifle?
     
  5. coyotezapper

    coyotezapper Well-Known Member

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    7MMRUM will do it with that long of a barrel(30"). I would bet you could do it with a 28" tube. My 7MMSTW will do 3000 fps with a 24" barrel. Match the powder burn rate to the length of the barrel. Long barrel slower powder, short barrel faster powder. Bergers will handle the velocity.
     
  6. jeffwhip

    jeffwhip Well-Known Member

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    Take a look at the 7MM AM made by Kirby Allen. He goes by "fiftydriver" on this forum. His rifles reach the speed you are looking for and I hear nothing but positive feedback about his rifles. I'm waiting until his new Raptor version comes out in a few months before I order mine. Follow this link and you can read all about it.

    http://www.longrangehunting.com/forums/f17/175-gr-smk-7mm-allen-magnum-47204/

    This may be exactly what you are looking for.
     
    Last edited: Feb 25, 2010
  7. Kiwi Nate

    Kiwi Nate Well-Known Member

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    I get best accuracy from my 7mm RUM and the 180 grain VLD at 3184fps. Barrel length is 26". Acuuracy is .3MOA with brake, .5MOA without the brake.

    Here is the math for a 30" barrel:
    35fps per extra inch of barrel.
    4 x 35fps = 140fps.
    3184 + 140 = 3324fps.

    When looking at ultra velocity 7mm's, you will need to compare the COAL's with the magazine length of your intended platform versus bullet jump. I use a stock standard M70 action (I could get the longer mag box from Wyatt Outdoor) so bullet jump is .400", thats nearly half an inch. Have a look at the various designs and see how they stack up in this regard. No doubt other posters will reply to my comments and help paint a better picture.

    The one aspect of long bullet jump that is often mis-understood, is the effect on the projectile's stability factor. The longer the freebore, the more skewed the angle of entry into the lands. As velocity and or twist rate are increased, the result is increased dispersion at the target. I think that some (but not all- i.e I don't know for sure) erratic performance can be attributed to the neglected issue of freebore versus stability.

    In my RUM, I have performed controlled tests to verify stabilty problems. If I seat a 168 grain Berger out long, I can load through the usual velocity ranges with acceptable accuracy- although by acceptable, I mean that groups hover around 1MOA. If the bullet is seated to fit the magazine, starting loads give 1MOA but as velocity is increased, groups spread out to 2.5MOA. The same result occurs with 162 grain bullets, including the stout jacket designs.

    I use a 4 groove 1:9 twist True-Flite barrel which does the job nicely with the 180 grain VLD. My wife uses the same barrel in her 7mm Rem mag and it works well with all bullet weights. My rig works fine but I would still urge you to look into the finer details as a lapua based Wildcat/ Allen Magnum might (or might not) offer less limitations than the RUM. A short throated RUM is a bit of a waste of time as the cartridge reaches max pressures very quickly, yet suffers other pressure related problems with start loads. Suffice to say, the 7mm RUM needs a kind of release valve before reaching full acceleration (sorry- that was a horrible analogy). You will lose about 100fps with a .200" freebore reduction in the RUM and will need to use only the slowest burning powders.

    Nate.
     
  8. trueblue

    trueblue Well-Known Member

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    The 284 JAZZ will do a solid 3200fps with the 180gr Berger.
    That last 100fps to get to 3300 does not gain you much, when you are already going 3200.

    Also, the 338 norma has already been necked down to 30 cal AI, its called the 300 JAZZ.