7mm RUM & 140 Gr Core-Lokt

Discussion in 'Long Range Hunting & Shooting' started by Doug in Alaska, Aug 23, 2009.

  1. Doug in Alaska

    Doug in Alaska Well-Known Member

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    I installed my new H-S Precision stock on the Rem 700, 7mm RUM and took her to range today. I had a bunch of Remington 140 gr. factory ammo. It was disappointing to say the least. I was shooting at 100 yards. First two shots would be in the same hole and the third would be 1 1/4" out. This is completely different than what I experienced yesterday with the .338, also with new H-S precision stock (it shot one hole groups all day long). I guess I better start working up the 168 gr. Berger loads and see how they perform. Have any of you guys had problems with the 140 factory ammo and the 7mm RUM?
     
  2. angus-5024

    angus-5024 Well-Known Member

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    what barrel contour are you using? Are you sure that everything is totally stress free? If two are going into one whole and a third way out there I would think that it could be something to do with heating, rather stress in your barrel or action, or your letting your barrel get too hot. I have a .338 RUM XCR and if I let it cool for between 7-12 min I can shoot a ragged hole at 100 yards (with hand loads), but if I let her got even slightly hot the groups open up fast.
    Have you bedded the action?
    Im sure that some more knowledgable guys will pipe up, but if that happened to me thats where I would be looking.
     

  3. Doug in Alaska

    Doug in Alaska Well-Known Member

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    It's a stock Remington SS barrel. I shot three shot groups and cleaned with BoreTech between sessions. The action is not bedded (didn't think I needed to with a H-S Precision) and the barrel is free-floating.

    Thanks for the reply.
     
  4. BIG MO

    BIG MO Well-Known Member

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    +1, its most likely by the third shot the barrel is heating up and the stress in your barrel is effecting your point of impact. Give it ten minutes between shots and see what happens. My .338 has alot of stress in the barrel. If I wait ten minutes between shots I get a tiny group. If I don't wait, I get an 1.5" group.
     
  5. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Several things come to mind, of which a couple have been mentioned. The 7 RUM is a fire breathing dragon. I know that with my 7RM the second shot gets the barrel warm and the third shot will get it hot if I dont let it cool long enough. I would think that with the RUM, after the second shot, that barrel is very warm unless you have let it cool between each shot. Combine this with the fact that you are shooting a factory barrel and sporter contour ( I assume it's not a varmit or Sendero contour) that probably has stresses in it and a little change in temp may affect it's dynamics quite a bit. The HS stock probably doesn't *need* bedding, but in this case, if the stock wasn't custom fitted to the action a little skim bedding might help and probably wouldn't hurt if done right.

    Also, cleaning after each 3 shot group might not be a good idea if you are shooting for groups. Your factory barrel might need to be fouled with one or two shots after cleaning. You might try cleaning the bore and then shoot a 10 shot string, letting the barrel cool between each shot, and see how the first couple or three shots group compare to the rest.

    Being a factory barrel, I would especially give the barrel a good break-in, cleaning after each shot until it stops or almost stops copper fouling.

    On ammo selection... if you are looking for a high degree of accuracy, you should be handloading with quality dies, bullets, brass, and powder. Use the corelokts for break-in.

    Berger VLDs coming out of a 7 RUM are going to be highly explosive at short to mid ranges. My first choices for bullets would be 160 AB's and 150 E-Tips, in that order, which ever shoots best.

    Just my thoughts, hope it helps...

    -MR
     
  6. Doug in Alaska

    Doug in Alaska Well-Known Member

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    Thanks for the help guys! I'll give your suggestions a try. I hadn't considered the fact that perhaps the barrel was overheating, mostly because it didn't seem all that hot to the touch. I understand what you are saying regarding the stresses in the factory barrel.
     
  7. J E Custom

    J E Custom Well-Known Member

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    +10

    I don't think you could get any better advice.

    I use to pull the core-lokts and replace them with a 140gr Ballistic Tip and they shot twice as good
    but now that the accubond has arrived that's what I would do or load the 160gr accubond.

    Just my opinion
    J E CUSTOM