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Thread: 338 RCM Load Data

  1. #1
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    Default 338 RCM Load Data

    Hornady published load data for the 338 RCM in their most recent reloading manual. Since I have a Ruger in 338 RCM I was eager to check out the data and I find it somewhat interesting when compared with Hornady's own data for the 338/06.

    Now I have used water to check case capacities between the two. The 338 RCM holds about 3 or 4 more grains than the 338/06 (A-Square version). However, looking at the load data in most instances Hornady shows heavier powder loads in the 338/06 than in the 338 RCM. Also, load data I have found on line show heavier loads for the 338 RCM than for the 338/06 with the same powder and bullet weights.

    So what gives?

    I have already safely exceeded the Hornady 338 RCM data with my handloads. Is Hornady keeping the loads low on purpose so that their factory loads look all that much better? To my mind the 338 RCM is nothing more than a shorter, fatter version of the 338/06 Improved. Both are good cartridges, but with the paucity of load data for the 338 RCM I'm not sure Hornady isn't doing it a disservice by essentially loading it down.

    Any thoughts?

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    Not much sense wasting time over it. Data in reloading manuals is simply a starting point. Some rifles are faster than the data published, some are slow Throat length can affect pressures as well.
    As long as your case life is good and the load is accurate be happy.
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    Also consider that the loading manuals have to deal with climatic changes worldwide. Hot arrid climates can raise operating pressures of cartridges to a point of over-pressure; Cool temps can reduce pressures. Reloading info has to allow for these variances.
    " Americans will never need the 2nd Amendment, until the government tries to take it away."

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    Brav01 - I agree with the temperature comment, but in this case (pun intended) when you compare load density in the same manual between the 338/06 and 338 RCM you have to wonder what is going on. I know from weighing the case capacity in water in both the 338/06 A-Square and the 338 RCM that the 338 RCM holds a few grains more. So why would the indicated loads be greater in the 338/06 than in the 338 RCM? Just makes me very curious, especially since my own reloading results show that I can exceed 338/06 powder charges in the 338 RCM without any signs of pressure problems.

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    I agree with what you're saying here. Capacity of the RCM is the same as my 338-06 AI. They do not respond the same, however. By that I mean, when working up, a one grain increase in each case does not produce the same increase in velocity this in same barrel length. The 06 case, be it Improved or not, increases velocity at a faster rate per grain change, than the RCM.
    So as it turns, my AI gives higher velocity with all bullets than the RCM, with same powder charge. Now I cannot say if RCM pressure us lower but velocity is. Generally when two cases have same capacity, like charges produce same velocity.
    Now of course, one rifle barrel may just be faster because of dimensions and smoothness. But all three RCMs I've used did the same as dud two 300 RCMs compared to standard 30-06. Are Ruger barrels slower due to friction? If so pressure is going up but not velocity. Beware!!
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    Murphy - You may be right about Ruger barrels. I take it your 338/06 AI is a custom barrel of some sort? It just may be smoother than the Ruger. Of course continued shooting should smooth it out eventually. The shorter, fatter cartridges are suppose to improve propellent burn efficiency, but I would guess there are too many variables involved to really see a difference based on case design alone. You say the barrel lengths are the same - 20 inches? What kind of velocity differences are you seeing between the 338 RCM and the 338/06 AI? Are you using the same bullets and powders? Thanks

  7. #7

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    I'll have to refer to MURPHY in the loading specs for the 338 RCM. AS, I have only fired factory ammo in my 338 RCM. I may however replace the projectiles in some of the factory ammo, in an attempt to get a stronger projectile in my rifle.
    " Americans will never need the 2nd Amendment, until the government tries to take it away."

    On the road of life..... Pot holes keep things interesting !

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    Quote Originally Posted by Steelhed8 View Post
    Murphy - You may be right about Ruger barrels. I take it your 338/06 AI is a custom barrel of some sort? It just may be smoother than the Ruger. Of course continued shooting should smooth it out eventually. The shorter, fatter cartridges are suppose to improve propellent burn efficiency, but I would guess there are too many variables involved to really see a difference based on case design alone. You say the barrel lengths are the same - 20 inches? What kind of velocity differences are you seeing between the 338 RCM and the 338/06 AI? Are you using the same bullets and powders? Thanks
    Yes agreed with the short fat powder burn efficiency but that is a very minor edge. Also barrel and chamber differences matter a lot. My 338-06 AI is a very smooth Shilen match barrel as is my 30-06 AI Mauser custom. This AI 30-06 will shoot factory 30-06 (as any AI should) at a higher velocity than any of my other three, 24" barreled, standard 30-06's. If you shoot standard -06 in AI chamber the case expands to fit that chamber and generally velocity is slightly lower due to less pressure from containment. Not the case with this gun. So unless we use the same barrel, which we can't we just extrapolate and monitor trends in the process and watch for signs of pressure. Good luck with the RCM. I like the cartridge.
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?



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