Twist Rate for 300gr SMK's in 338/300 RUM?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Don - In Idaho, Dec 27, 2005.

  1. Don - In Idaho

    Don - In Idaho Well-Known Member

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    Twist Rate for 300gr SMK\'s in 338/300 RUM?

    Have any of you built a rifle in this chambering? I plan to shoot mostly 300 Grain SMK's but may try some higher BC VLD bullets down the road.

    Recommended twist rate that will stabilize the longer 'custom' 300 grain VLD bullets out there without winding the 300 SMK's up too fast?

    Recommended chamber neck diameter using Fed. Gold cases and Rem. cases?

    Also which bullets would you recommend my trying out besides the SMK?

    Currently considering:
    338/300 RUM throated for 300 SMK
    Tight neck (not sure what to get here....)
    Pac Nor 30" Supermatch barrel
    Holland Brake
    1:10 Twist 3 Groove


    Thanks!
     
  2. davewilson

    davewilson Well-Known Member

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    butch keen just built one of these,can shoot the 250 gr lapua at 3400.not sure of barrel length,at least 30".killed a few with it this year,600 was the farthest.excellent wound channels.i'm leaning towards building a lapua. better brass, not a wildcat.
     

  3. 1doug

    1doug Well-Known Member

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    thats the same as Shawn's 338 edge do a search for it. it went about 80 post deep
     
  4. Shawn Carlock

    Shawn Carlock Sponsor

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    I mostly use 30" Hart barrels 1-10 twist with the 300 gr SMK, H1000, Retumbo, or RL25. 2900 fps or so. I have yet to build on of these that won't go under 1" @ 300 yards. I don't tight neck them, I don't believe that it is a great benefit here for the extra work. I use minimum spec demensions for the 338 Ultra in the neck area. Some guys neck down 375 Ultra and then turn the necks. I have run oal's from 3.685" to 4.000" and seen less than 50 fps difference in velocity when seated to the lands. I would give the wildcat bullets a try I used some of the 300 gr.WC bullets with great results. I keep bitching that Nosler doesn't make a 280-300 gr. Accubond, that would be hot.
     
  5. Don - In Idaho

    Don - In Idaho Well-Known Member

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    Thanks for the tips guys. I have a 338 LM Armalite and like it quite a bit, but based on what I have read, I am 99.95% convinced that the 338 LM is not a safe round in the Remington 700 or Savage 110 actions which is what I would be building the rifle on. I am plenty happy with the last batch of Remington 300 RUM brass, getting sub 1/2 MOA groups with my 300 RUM and 180 SMKs, but I will definitely try the Fed Gold 300 RUM cases.
     
  6. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    A properly fitted Rem 700 will easily handle the Lapua case. That said, the 338 Edge is a much easier fit in the Rem 700 and will get you the exact same performance as well.

    As far as rifle build cost, the 338 Edge will cost less because there is no need for bolt mods like there is with the Lapua case head size. Thats one of the best features with Shawns Edge, Lapua performance in a simple to build package!! Good design, more practical then some of those crazy wildcats that loon north of Shawn is building in Montana /ubbthreads/images/graemlins/grin.gif!!

    Good Shooting!!

    Kirby Allen(50)
     
  7. Don - In Idaho

    Don - In Idaho Well-Known Member

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    Savage did some extensive pressure testing work on the WSM rounds and found that the WSM in a barrel with a 1.05 shank had a 98% safety margin window, which is enough for a reasonably safe build, but it still isn't 100%. They now only chamber the WSM's and RUMs in their larger thread size to exceed the 100% safety window.

    The Remington thread shank at the root is even thinner than the Savage at 1.010".

    The Lapua case is 6.5% larger in diameter than the WSM cases reducing the already too thin chamber wall even more. The LM case head is also 9.5% larger than the WSM case head, increasing the bolt thrust on top of the too thin chamber walls.

    I don't know how those numbers relate to the 98% window but they definitely reduce the safety margin even more.

    If you are loading the LM to the same pressure levels of the WSM, it sure looks like an unsafe build to me.
     
  8. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    LongrangeSupply,

    Just curious if you have any documented cases of a Rem 700 based 338 Lapua coming apart with the use of proper 338 Lapua load levels?

    Most of the modern receivers I am aware of are proof tested at twice their working chamber pressures so we are dealing with pressures up to or over 100,000 psi.

    Now I can tell you that you will pierce a primer or loosen a primer pocket well before you get anywhere near this level of pressure. In fact more cases will start to loosen their primer pockets in the 65,000 lb range to some degree depending on their chamber design and fit.

    I will also say that if you are loosening the primer pockets on a 338 Lapua case no matter if its as the standard 338 Lapua or any wildcat based on that case, you are pushing the pressure far to high and need to dramatically reevaluate your loading practices.

    One aspect of the Savage barrel is that it has a relatively small diameter Barrel shank diameter over the shoulder area of the chamber, Over 1/4" smaller in diameter then the Rem.

    Also keep in mind that there was a Savage rifle chambered for the 7.82 Patriot. This Lazzeroni short magnum has a lapua case head diameter.

    I do not advocate using the Savage with the Lapua class case but I do the Rem 700 when used properly in properly fitted rifles.

    There have been thousands of Rem 700s built and chambered for the Lazzeroni short actions and long actions which all use nearly the same case as the Lapua only in a slightly improved design.

    There have also been alot of Rem XP-100 handguns chambered for the Lazzeroni short action magnums and used to full potential with no problems at all.

    Ever measure the barrel shank diameter and receiver diameter of a Sako TRG-S? I suspect the barrel shank is less then a Rem 700 and the receiver no larger.

    Same with the Wby MkV receiver. Same barrel shank diameter and receiver diameter.

    Again, a factory Rem 700 receiver, certainly not, but a properly squared receiver with 100% lug contact and a precise fitted barrel and min spec chamber design with responsible load levels, you bet.

    Kirby Allen(50)
     
  9. Shawn Carlock

    Shawn Carlock Sponsor

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    LRS,

    I to have built several 338 LM's on Rem 700 receivers with no problems at all. I believe that all other things being the same that the critical area is bolt lug shear strength and not barrel shank diameter that is encapsilated by action diameter. Actions are proof tested far beyond the levels of responsible handloading. I have no issues for action strength. My concern for strength stems around a mistake or repeated firing at near proof level loads. We all know guys that shoot loads that ruin the brass in 1 firing, in the interest of max velocity, despite repeated warnings against it. These guys will usually set the lug back before anything and create an excess headspace problem. Then they have a case rupture or 2 and come to talk about the poor work you did on their rifle. Since you are obviously fall on the safety side of the line I wouldn't have any concerns about building the LM on a 700. The LM in the 700 has some issues that need to be addressed by your smith when they build the rifle but action strength is not one of them.
     
  10. Don - In Idaho

    Don - In Idaho Well-Known Member

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    Re: Twist Rate for 300gr SMK\'s in 338/300 RUM?

    I am not saying that I think that a normal pressure load is going to fail in a Rem 700 or a Savage small thread action chambered in 338 LM but the facts are clear as I understand them, that it is without question less than a 100% setup safety wise.

    The Savage testing giving below 100% safety margin with the WSM's had absolutely nothing to do with lug strength, but rather chamber wall thickness. It is in marginal territory with the WSM and even more so with the Lapua. Remington barrel shanks are thinner than Savages behind the shoulder and thus would be more prone to failure than the Savage barrel in that area. I have also talked to some smiths who are seeing chamber wall stress cracking in Rem 700's chambered in WSMs and will not install WSM barrels on them. Since the Lapua Mag has even thinner walls, I just don't want to go there myself.

    Based on that knowlege, I won't be chambering any 700's or small thread Savages in 338 Lapua.