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Thread: slow speeds?

  1. #1
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    Default slow speeds?

    I shot a couple of my rifles through the chronograph this past weekend, and got some surprising results. My 7-08 shot speeds comparable to the listed speeds in the manual, but my 7mmRM shot WAY slow.

    Here's an example: Shooting a 160 gr Accubond loaded with RL-22 to the the max level listed in the Nosler manual (I can't recall the exact number an don't have my notes here right now), the 7mmRM shot about 2800 fps, which is more than 300fps slower than shown in the Nosler manual. My Ruger M77 MKII has a 24" barrel, the same length Nosler used.

    Even loaded a grain or two above the max listed load, I still wasn't even close to listed speeds.

    The same was true for RL-19, the other powder I tested. All loads of both powders were 300fps slower than what is listed in all the manuals I referenced.

    I don't think my chronograph was off since the 7-08 was shooting about 2850fps with 140 grain Accubonds with various powders, which is right in the correct range for a 22" barrel.

    What could cause such a large difference?

    I should mention that even the loads that were a grain or two above the max load listed in the Nosler manual showed absolutely no signs of excess pressure. No primer issues, no base expansion or bright spots, no sticky bolt lift. Should I just work up to higher load levels? If so, what sorts of things would cause this rifle to require more powder to get the same pressures and velocities?

    Thanks!

  2. #2
    Member RMiller's Avatar
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    Each rifle is unto its own.

    I have a slow 30-06 and have had slow 300 win mags in the past.

    Sometimes they are slow because max is higher for those rifles but a grain or two of powder is not going to give 300 FPS in these cartridges.

    I should mention that even the loads that were a grain or two above the max load listed in the Nosler manual showed absolutely no signs of excess pressure. No primer issues, no base expansion or bright spots, no sticky bolt lift. Should I just work up to higher load levels? If so, what sorts of things would cause this rifle to require more powder to get the same pressures and velocities?
    When I work up a load I look at what the chronograph is telling me. When working up I look for velocity to flatten out or even go down with a higher charge. This tells me I am beyond max wether or not any of the mechanical signs exist.

    For a rifle with a max spec chamber and brass fully sized it would be like fire forming loads every time. It will greatly reduce the velocity. If you neck size your brass you will be using brass that is made to fit your chamber.
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  3. #3
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    Default interesting!

    Thanks Miller!

    As a matter of fact, I was shooting new brass (see earlier post on the subject) out of this rifle. It makes sense that this might suck up some some energy. And as a matter of fact I did clean and prep the now once-fired cases just last night, and did neck resize them only.

    I also looked over the velocities of the various loads in my notes. I didn't see any obvious flattening of the velocity curves. I'm thinking in "round 2" I'll start a grain or two below my highest load in round 1, just in case pressures are significantly different for the now once-fired brass, and work up from there. It'll be interesting to see if there is much difference in chronograph readings at similar powder levels, as well as group sizes. Fun stuff!

    Thanks for the input. It was aware of but hadn't thought of in relation to speed. Anyone else with input, insights, or past similar experiences, please don't hesitate!

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    This is a good puzzle. I have a couple of insights about it. RMiller is right the size of the chamber will determine the size of the vessel, the cartridge case. If it is bigger it will take more powder to achieve the pressure of a smaller test chamber. Keep that in perspective but that is generally true. I don't think there will be a measurable difference between the new vs fired brass, each time the brass expands to fill the chamber. Nor would we see difference between full sized vs neck sized. Granted some energy is consumed filling out the case but we can't measure it.

    Also rifles with the exact chamber dimensions can still have wide spreads in velocity because of other factors. The barrel dimensions are often of greater significance than chambers. If the bullet fits the barrel well and plugs it tight the pressure stays higher longer, giving a broader pressure curve and resulting in higher velocity. This appies to the throat as well as the rifled barrel. Also some barrels are just rough as a cob. Friction is higher and velocity is lower as a results.

    Another factor since you're using RL-22. Some years back about the time that Alliant became the purveyor of that powder, the formula changed. That stuff is made in Sweden and exactly when the change took place I can't say but it did change. I think I read about it in some writings of Ken Waters. But at the time I got some of the new and compared it with some of the old and looking through my notes last night I found it with the 308 Norma. I also used it with the 30-06 and a seven mag and there was about a 1.5-2.0 grain difference to get the same velocity. It required more of the new lot. Your referenced Nosler manual may have developed loads with the older lot. All these factors together will certainly work to lower velocities in your Ruger.

    If you had used RL-22 before with the chronograph and had different results now it would be a different issue. My guess is this is the first 7 mag/RL-22 over the chrony, eh? I think you could safely get higher velocity from the combo but rather than look for pressure signs I would rely on the chrony. I would charge cases as you see fit with five rounds each with 1.0 grains increments (no more no less) between loads. As an example starting at about 3 grains below max, 71.0 grs, 72.0 grs, 73.0 grs, 74.o grs etc. I don't know that these weights are correct, just examples, so don't use my numbers. Then plot the fps per grain of powder such as 56 fps, 61 fps, 48 fps, 41 fps, 28, fps. Now this is the important part. Loading six different loads one grain apart in charge weight, will give you an approximate gain per grain . When you have a load that gives half the amount of the first stable load, as the example above, the max load is the previous load. In the example the max would be the 41 fps load. The charge that is the first stable load is the 61 fps gain load. It is stable because that is the one where it stopped increasing in velocity.

    You can load a load of five then try five at 1 grain less powder then 1 grain more, back and forth, keeping track (good notes). This is best to be sure you aren't at max when you start and keep the flow of data linear. I usually use five different loads at one grain increments. It may not be this simple but you get the idea. You mentioned flattening of velocity curves and that is what we are looking for, the knee of the curve. You're going at it correctly. All of this would have more meaning if we fired ten shots rather than just five but you are really just looking for general concepts here not exact data. In the example above the gain is about 60 fps when stable and we are lookin for a 50% drop in that, then back up one grain. The 50% drop load is over max. I use one grain because of the size of the case, 30-06 to 2.5" belted mag size I use one grain. In the 223 size, it would be .5 grain increments. I use this technique because I used it when running pressure equipment and discovered this concept to hold true for many calibers. The thing to remember is the back side of the curve is sharp and volatile. The one grain increment can be plotted and will be a sine curve until we get beyond the knee, then it drops and can reverse. Meaning an increase in charge weight can cause a drop in velocity. One test, just like one shot doesn't prove anything but you'll see how this works after a few dozen calibers, a few hundred loads and a few thousand rounds. Good stuff here. Good luck with it and keep us posted.
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  5. #5

    Default Check

    Did you use a magnum primer in the 7 Mag instead of a regular primer for the 7-08? How old is the powder you are using to load? What temperature was it when you were on the range (some powders don't like cold)?
    Good Luck with your problem !!
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  6. #6
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    Default

    I'll echo what brav01 said. How temperature sensitive is RL22? I know some of my loads with IMR and other Alliant powders are slower in the winter. The Hodgdon Extreme powders seem to be the most consistant with varying temps.

    Dan

  7. #7

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    I'm a believer in using temp stable powders, but I dont think that would account for a differnce of 300 fps... 50 fps maybe and it didn't affect the .08 I would want to know more about the rifle... the action, chamber, throat and bore. How old is it? How many rounds have been through it? How has it been maintained? What condition are the action/bolt, chamber, throat and bore in? Have you chrony'd factory ammo through it?

    My guess is that an examination by a good smith with a bore scope might reveal a lot.

  8. #8
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    Reloader 15 says consistant at all temperaters. FWIW.

    An extreme example with the fire forming idea bringing down velocites would be firing a 375 H-H in an improved chamber. Using factory 375 H-H ammo typically loses 100 FPS or more when fired in an improved chamber rifle. If a factory load is normally 2520 FPS for the factory load it may barely get 2400 FPS when fired in an improved version chamber.

    I keep saying improved because I do not know which chamberings can use factory ammo. Not all of them can. With the belted cases it may not be a big deal.
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    Default update

    Well, my internet connection at home got fried during the wind-storm caused power havoc last week, so I haven't been able to check in until today. Looks like I missed some good advice! However, I do have some new facts to report.

    First of all, CCI-250 was used for all of my 7mmRM loads. Primers can be ruled out. Nor do I believe that the RL powders would show THAT much temperature variation. The gun has fewer than 500 rounds through it, probably less than 250. It's been hunted with for over 15 years, and the wooden stock shows it and the barrel has a spot or two from some wet nights out, but the bore is not rusted.

    I did make it to the range for about 45 minutes on Saturday and then for a few hours yesterday. On Saturday I got around to testing the loads with RL-25. Bingo! More velocity and a 1/2" group. Yesterday I came back and fired some more loads with both RL-22 and RL-25. I did something similar (but not nearly as in depth) to what Murphy proposed. I went up in 1 grain increments, up to and then beyond what was listed as "book max" loads. With both the RL-22 and the RL-25, I did not see a significant drop in "gain per grain" with any of the loads I tested. I never did reach the speeds shown in the manual with RL-22, but I DID reach them with RL-25, at about 3 grains beyond the book max. Since I was working in the "above max grains" area, I kept a very close eye on pressure signs, and never did see any, with either powder.

    What I think I'm seeing here is what Murphy described early in his post. For whatever reason, my Ruger M77 seems to require more powder to achieve the same pressures, and hence velocities. I just finished shooting all the new brass, so now I have once fired brass to neck size and REALLY dial this baby in. One further note: This gun does seem to be very sensitive to bore fouling. I noticed this when the first 3-shot group I shot on Saturday with it (RL-25, 69 gr) was 1/2". The next group (at 70 grains) was more like 1.5". Then I cleaned the rifle and the next group (71 grains) was back below an inch. Cleaning this rifle is also much more of a chore...it takes about three times as long to get copper fouling out of it than any of my other rifles. This supports the idea that it does have a bore that's a bit rough. However, since it doesn't seem to be causing too much pressure and excellent accuracy is still achievable (at least for 3 rounds!) I'm going to live with it.

    Since I was getting 3060 fps from Nosler Accubonds and RL-25 and still shooting groups at or below MOA, I cancelled any further testing with RL-22. No point in going to even higher loads with RL-22 to achieve what I've already achieved admirably with RL-25. RL-25 definitely seems like the powder for this rifle/bullet combo.

    I might also add that yesterday I got my Kimber 7-08 to shoot sub MOA groups too, and my 375 H&H is only about 1/2" beyond that currently. Not bad for three factory rifles! Isn't this fun?

  10. #10
    Member DanAKAL's Avatar
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    Really good info here! Thanks for the update. Seems as though you have found what your rifle likes.

    Not sure what you are using to clean your barrel but if you are anything like me I use liquid type cleaners. Usually Butch's but I have some Hoppes and Remington Brite Bore. I have encountered rough barrels before and always saw an improvement after cleaning it with Remington Bore Cleaner, the paste type. I suppose this cleaner is somewhat abrasive so it smooth's out some of the rough spots in the barrel. Might be worth a try.

    Again, thanks for the update.

    Dan

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    Default bore cleaners

    My cleaning routine has been to run a patch with Shooter's Choice bore cleaner through the bore to start with. (I tried Hoppe Bench Rest 9 previously but couldn't stand the strong smell and it didn't seem to work all that good anyway). I then dry patch once, and then wet a brass brush and run it back and forth through the bore about 20 times each direction. Then I dry patch again. By this time all the powder and lead fouling is out, and on most of my guns almost all the copper is out too...but not on the Ruger 7mmRM. For it, I get out the Barnes CR-10. This is an almost clear ammonia-based cleaner, which I like since it turns blue when it dissolves copper so I can visually see if there is any copper left. With my Kimber 7mm08 and my Model 70 375H&H, if I run patches soaked with CR-10 through the bores at this point they come out with almost no blue at all right away, but on the Ruger 7mmRM the patches come out dark blue for about 6-7 patches, and then start getting better. By about the 13th CR-10 soaked patch they start coming out nearly without blue and I can go back to shooting.

    Like I said, compared to my other rifles, cleaning this one takes three or four times as long. This was my first rifle, and I never knew jack about copper fouling back then so I never did more than run a little Hoppe's powder solvent through it from time to time. I suspect it just kind of glazed with copper, and maybe I'm still mopping up some of that today. Live and learn.

    Maybe I'll try some of that bore paste you mentioned. Thanks for the reply!

  12. #12

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    If you suspect heavy copper fouling, I would recommend trying Wipeout. It will get rid of all your copper. It may take a few soakings, but it is thorough. I did this with my old hunting rifle... had to soak it about 8 times, up to 8 hrs each, but it got all the copper out which was confirmed by a bore scope. That barrel was spotless.

    If you have a barrel that fouls easily and not broke in, it might be difficult to break in after 250-500, not really sure??? You could always try it and see what happens. It would be an interesting experiment

    Good info on sharing the better results with the powder change. Keep up the good work

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