7 RUM Max Velocity

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Dean2, Aug 1, 2010.

  1. Dean2

    Dean2 Member

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    The gun is a LH Remington stainless with a 26" barrel. Aside from being glass bedded, trigger redone and having a Pachmeyer declerator and mercury supressor added, it is box stock. If shoots the Hornady 162 grain SST into less than 1.5 inchs at 300 yards. I have used these bullets to kill one moose at 380, another at 175, a couple of black bears, one elk and a number of incidental deer.

    I have to date shot it somewhat downloaded with 78 grains of 4831, a Winchester mag primer and the 162 grain SST, as the longest shot likely in the area I have been hunting is only 400 yards.

    I am about to start working up a load for long distance antelope and deer on the open prairies where shots can be VERY long. What is the maximum velocity you have derived in a factory stock Remington with a 26" barrel using the 162 grain Amax. (Want to use it for its .625 B.C. as it is also often windy out on the flats).

    Of the likely powders to do this with 7828SSC, 869 and Retumbo, which have you found to be the best. I don't need loads as I will work them up anyhow, but a starting place for previously tried powders and what to expect for reasonable max velocity would be helpful. Thanks for any info.
     
  2. Dean2

    Dean2 Member

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    I have been working on these loads. As far as 162 Grain Hornadys. so far Retumbo is giving far and away the best velocity. 95 grains is producing 3450 FPS, and 3/4 inch groups at 100 yards. This is over 250 FPS faster than I can get with 7828 SSC at max loads. I am about to shoot this load at 300 yards on out to 800 to see if the accuracy holds at long distance. Anyone else have any experience wit hRetumbo in this round?
     

  3. sambo3006

    sambo3006 Well-Known Member

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    That is extremely high velocity. I would suspect your pressures are way up there and brass life will be very short. I'm running the same rig and with 150 gr ballistic tips I'm getting flattened primers at 3400 fps.
     
  4. RockZ

    RockZ Well-Known Member

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    US869 should give you the most velocity with the least pressure.
    A buddy and I worked up loads with his in a 28" barrel with US 869 and got very good results with the 180 gr.
    I don't remember the exact velocity but it was very good as well as accuracy.
     
  5. Dean2

    Dean2 Member

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    The velocity is high, actually over book at that charge weight but they were using a 24" barrel and I am using a 27". Since velocity equals pressure and all that you would think they are running hot, but the primers are not at all flat or cratered, no ejector marks and the base of the cases mike within .001 of a fired factory case ther is no evidence of excess pressure. Also, the brass I am shooting these out of have 6 loadings on them, are only neck sized, still chamber very smooth and were trimmed once at the 4th loading, so brass life is fine so far.
     
  6. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Your WAY above average for that chambering. I build alot of 7mm RUMs and in your barrel length, average velocity out of my min spec chambers will usually run around 3300 fps max.

    Now some will run a bit faster, some a bit lower but thats pretty close to averge for a 160 gr class bullet weight with a match barrel and match chamber and throat.

    Sometimes rifles do not show pressure signs, sometimes you get a very fast barrel but as you mentioned Velocity is simply a funtion of pressure and bullet time in the bore. Powder charge really does not mean much, its the end product, Velocity, which will tell you more about pressures then anything.

    Again, I would say your way over pressured for this chambering. Hell your running right close to my 7mm Allen Magnum with same barrel lengths. My personal lightweight 7mm Allen Magnum gets me 3500 fps with a 160 gr Accubond in a 26" barrel length but that round is based on the larger improved 338 Lapua design which is VASTLY superior in strength to the RUM.

    My only concern is that you run into a case with a flaw in the case head or something like that. If that happened, you could have disasterous results with that pressure.

    You are reading all the pressure signs correctly except for one, and the velocity is often the most accurate pressure sign you can have but the one we most often fail to listen to. Again, 3300 fps is about max I have seen from most of the custom rifles I build, 3350 fps on the outside. Much over that and I would say your running things to hard even if there are no other pressure signs.

    In all honesty, I would recommend stepping up to the 180 gr Berger, drop velocity down to that 3150-3200 fps range and you will get better long range performance ballistically with that bullet if your looking for true long range performance.

    Hope this helps some.
     
  7. Dean2

    Dean2 Member

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    Kirby

    You make perfect sense and your experience with this round is way more extensive than mine. Great post and I truly appreciate you taking the time to type that out. I will re-Chrono these and back them down to 3300-3350 max. I have been loading for over 40 years and the one thing that has been universally true is that the laws of physics don't change. I have never had an incident from loading my own and it isn't worth the chance having one for 100 fps. All the best.:D
     
  8. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    In no way was I questioning your experience level so if I offended you I apologize to you as that was not my intention.

    There are situations where a specific weapon system will get dramatically faster velocity then it really should. I have had a couple of those in my shooting carreer. One also gave me quite a scare. It was a Ruger M77 chambered in 7mm Rem Mag. This rifle was scary fast and showed no pressure at all. I loaded the 140 gr Ballistic Silvertip up to 3440 fps with no pressure signs of any kind.

    One day I loaded up a new batch of brass with my favorite load and went out to check the zero before hunting season. First two shots went off great, third shot blew the floorplate off the rifle and cracked the stock walls around the mag box........

    Luckily I was not hurt in any way, scared crapless!!! but unhurt. I wanted to find out what the hell had happened as I had shot several hundred of these loads through the rifle and then all of a sudden, BOOM!!!

    Well, it took me a long time to figure it out but what I found that caused the problem was when I looked in the box of virgin brass, out of the remaining 50 rounds of brass, 5 of them had spider egg sacks inside the cases. These egg sacks took up a decent amount of case capacity but because they were relatively pliable, they still allows the seating of the bullet without much notice as I was not really paying attention to this.

    Still, because I was running on the ragged edge, it was just enough to spike pressures enough to blow the primer pocket severely and the flame cutting blew out the case in the controled round feed cut out of the bolt face which allowed the gas to take out the mag box and side walls.

    Learned two things with this lesson, 1. Check your cases before you load them!!! 2. Don't push things to the red line, "JUST IN CASE!!"

    Things happen and it never hurts to have some margin of error on your side!!!
     
  9. Dean2

    Dean2 Member

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    Kirby

    You absolutely did not offend me. I have never been shy about taking advice from someone with lots of knowledge and experience and you clearly have that. No matter how long you have been doing something, the day you quit learning new stuff about it, is probably the day you aught to give it up. I reaaly do intendd to listen to your adive and back this load down 100 to 150 fps, just so there is a good margin of safety. Thanks again.
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Its nice when you are able to "download" your rifle to get into the average velocity range you should be.

    On the other end of the spectrum is kind of hard to take. When you get a slow rifle, its hard accepting being 100 fps under where you should so your problem is a very good one to have!!!

    Good Shooting!!!