velocity FPS spread???????

Discussion in 'Reloading' started by jeff 300, Nov 7, 2007.

  1. jeff 300

    jeff 300 Well-Known Member

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    what is a good spread on your speed? mine is jumping all over the place. I'm shooting a kirbybuilt 338edge with retumbo and h1000 with 300gr smk's. both powders are doing it. the h1000 is not as bad but still. am planning on running just the h1000 and got a 8# can the other day. could this be a bad chronograph. i have the shooting chronoy F1. i know it's not the best but thats what i have. all of the groups where shot in good sun light about 10 feet in front of the barrel.

    a 3 shot group 92 gr of h1000 2856,2819,2834

    92 gr retumbo 5 shot group 2846,2847,2860,2809,2821

    93gr retumbo 7 shot group 2884,2828,2836,2867,2857,2854,2876

    is this as bad as i think are am i just over doing it? i see some guys get only a 10 fps change but all of mine way over that?
     
  2. Boss Hoss

    Boss Hoss Well-Known Member

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    I shoot 1k competition---I have won State Championships before, hold the range record for closest to the center of the x in last years 1k championship in Missouri and I prefer a 10fps spread but will accept a 25 fps on my loads and I am using almost half the power you are in my 6.5 x 284. The first load shows promise now this is something that you HAVE to do when shooting over the chrono!!!!!!!!!!!!!!!!!!!!!!! Make sure you have the sight picture and the rifle is perfect in the bags then close the bolt and fire within a couple of seconds. Why you ask ------ well as the round sits in the chamber the round begins to absorb heat from the chamber and that will cause different pressures to form during ignition thereby causing velocity spreads and different impact points if shooting at extreme ranges.

    All of this being said on my big boys that hold 80 to 110 grs of powder I keep working until I get a 5 shot string under 40fps… Most of mine are in the 10 to 25 range but my 300 Slowpoke (started out as a 300 RUM) is right at 38 fps on the high to low extreme spread but shoots .5 MOA at 600..
     
  3. jeff 300

    jeff 300 Well-Known Member

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    Thanks a lot. i never thought about the heat in the chamber. but that make a lot of scents to me. where are you at in Texas? What kind of scale do you use. I'm using a rcbs charge master. i will be trying the h1000 more to see where she's going to top out at. kirby tested it with 93gr of retumbo and got 2950 out of it. if i can get that kind of speed and have good tight group under 1/2 moa with h1000 i'll be happy.
     
  4. stxhunter

    stxhunter Well-Known Member

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    jeff i had the same problem working up a load of retumbo in my 300 ultra. I was not letting the gun cool down enought and when i loaded a round if i waited to long to squeeze off the shot it would cook the round and i would get a jump in velosity.I have a ced millinium chrono if you would like to use it call me 658 2665
     
  5. Boss Hoss

    Boss Hoss Well-Known Member

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    Jeff I am in the DFW area and I use the same scale you do but it weighs about .3 gr light and I trickle the rest onto my Acculab scale. Just a habit I have gotten into from competing. All of my Wilson Seating dies were also cut with the finish reamer used to chamber the barrel.

    David
     
  6. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Low extreme spreads are certainly what you want but it may not be as critical as many thing. I can not say how many customers I have had that came into my shop or e-mailed or called wanting to order a rifle. They will will say they want a top end rifle that will hold extreme spreads in the single digits.....

    I then as, wouldn't you rather have a tight grouping rifle and they often reply that if you get low spreads, you WILL have 1/2 moa groups or better.

    Simply put, and I will be blunt as always, thats simply BUNK!!!!

    If your dealing with small capacity, small bore BR rounds, it is possible to get extreme spreads in the single digits.

    When you jump up to a +90 grain capacity case in a faster twist barrel with a very heavy, long bullet driven to upper velocity ranges, it becomes much more of a challange to get those single digit extreme spreads.

    That is not to say its not possible, I have shot several strings through my 338 AM that had single digit extreme spreads. That said, the same exact lot of ammo tested at a different time would have up to 30 fps spreads........

    In my opinion, in a chambering in the class of the Edge, if you can get extreme spreads under 30 fps, you will get fine accuracy at long range if the rifle like that particular load. If you can get better, great, if not, I would not sweat it.

    Group size is what is critical, not extreme spreads. Yes, long range groups will show velocity spreads for sure, how much, depends on how accurate your rifle is and how well you can shoot.

    I have shot 1/2 moa groups at 1000 yards with loads that have 40 fps spreads. I have also shot sub moa groups at 3000 yards with the same loads.

    I have also seen loads that were in the teens for extreme spreads not be able to hold better then 2 moa at ranges past 500 yards.

    Simply put, shoot the rifle at long range, if a load groups well, that is what is important, DO NOT pass on a load just because of extreme spreads that are a bit higher then you like to see.

    I had one customer come in complaining about a rifle I built him that he could not get under 15 fps extreme spreads. This was a semi heavy 300 RUM. We took the rifle out and I shot it at my 450 yard range behind the shop. After shooting three shots over the chrono and printing a sub 1/2 moa group, the customers only comment was, SEE, those three had a spread of 35 fps!!!! I literally had to put the group in his face to see how the rifle would shoot and to not get so hung up on ES.

    If she shoots, thats the critical thing, do not get to hung up on ES. In my experience, if a rifle likes a certain bullet, you will get fine accuracy with any load that gets you ES under 50 fps or less. Again, if you can get fine accuracy with low ES, great, but do not pass on an accurate load because the ES is a bit higher then you like.

    Kirby Allen(50)
     
  7. Boss Hoss

    Boss Hoss Well-Known Member

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    At 1k a 50fps is just about the limit for me (sporter rifles that use over 80 grains) as even with the for example 190 30 SMK I use the difference at 1k is 8.5 inches to some that is not a lot but to me it is. Granted the load has to shoot (group well) but most folks do not have the knowledge, equipment or skill to properly set up a rifle to Truly evaluate its potential at 1k. Most use shorter ranges and extrapolate which is something that I am fortunate not to have to do. Just do not downplay the potential for vertical dispersion at 1k because it can make a big difference both shooting at animals and in competition which I know is not the subject but still has relevance.

    The takeaway here is having as few variables as possible and your chances of success are always better…
     
  8. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    Boss Hoss,

    You are in fact correct in your comments, but there are ways around this to some degree. Let me explain. The main reason for developing my Allen Magnums in conjunction with Richard Graves Wildcat bullets was to get extreme BC bullets loaded to upper end velocities for what is common with current magnums and conventional bullet weights.

    Why do this, well, you offer the explination in your post about your 190 gr SMK having 8.5" of vertical variation with only 50 fps muzzle velocity spreads at 1000 yards.

    That may well be with conventional bullets at the velocities you can get with conventional magnums. I wanted more so I designed my Allen Magnums and all are similiar to what your about to read. These numbers are concerning my 7mm AM in a 30" barrel shooting the 200 gr ULD RBBT to a velocity range of 3250 fps up to 3350 fps.

    1000 yard drop numbers with 500 yard zero

    3350 fps -106.4"

    3300 fps -109.9"

    3250 fps -113.5"

    Now with your example, you get 8.5" of vertical variation for every 50 fps, my 7mm AM cuts that dramatically. If we go from 3350 fps down to 3300 fps, the veritcal variation will only be 3.5" Well under 1/2 moa and to be honest, not enough that most people will ever be able to see this on target from field shooting postions at 1000 yards.

    Even if you drop 100 fps, 3350 fps down to 3250 fps, you only have 7.1" ofo vertical variation. Now certainly you do not want 100 fps spreads if you can help it, BUT, with the ultra high BC bullets and moderate to high velocity, you can pretty much change the thinking as far as vertical variation compared to conventional chamberings and bullets.

    If we look at the first example, the 338 Edge, lets compare the numbers again.

    1000 yards with 300 gr SMK at 2950 fps.

    2950 fps -146.9"

    2900 fps -152.5"

    2850 fps -158.4"

    So dropping from 2950 fps to 2900 fps in velocity, a 50 fps spread, will result in a 5.6" vertical variation, again right at 1/2 moa, again, better then most can hold shooting from field conditions.

    Again, a full 100 fps ES will result in 11.5" of vertical spread. Again, no one would be happy with a 100 fps spread but this goes to show that the vertical shift in impacts is much less then many would think.

    To reinforce my comment about ultra high BC bullets pretty much taking this out of the equation, lets look at what the prototype 265 gr AT RBBT would offer in this same chambering. But we can get more velocity with the lighter bullets but they have a higher BC with the .89 BC I have found these bullets to have at around 3100 fps.

    1000 yard

    3100 fps -125.1"

    3050 fps -129.6"

    3000 fps -134.3"

    So dropping from 3100 to 3050 fps, 50 fps spread, your looking at 4.5" variation is all at 1000 yards. With the full 100 fps spread, just 9.2" of variation, not much more then your 30 cal example but again more then you would want but its pretty easy to get any load to under 50 fps spreads.

    The final example I will offer is about the ultimate in ballistic performance we are playing with. The 338 AM loaded with the prototype 265 gr AT RBBT to 3500 fps. We will go +/- 50 fps from this velocity as its the standard velocity with this bullet in my AM.

    1000 yards

    3550 fps -93.8"

    3500 fps -96.7"

    3450 fps -99.6"

    lets keep going!!

    3400 fps -102.7"

    So from 3550 to 3500 fps, 50 fps variation, you will have 2.9" vertical variation at 1000 yards. Well below most can hold groups to and even less then many of the best rifles in the world can hold groups to.

    Even dropping a full 100 fps in velocity spreads, 5.8" vertical spreads, still right around 1/2 moa.

    Even a full 150 fps velocity variation will result in only 8.9" vertical variation on target at 1000 yards. Roughly the same as the 30 cal example with three times less velocity spread.

    This is why its so easy to hit targets at 1000 yards with the 338 AM compared to other chamberings. Now remember I am only referring to the velocity variation here. Other factors come into play dramatically but with the modern ultra performance wildcats, extreme spreads in velocity do not need to be held to the standards that out fathers did when they were shooting at long range. Simply not as critical with new componants.

    Now, is the 338 AM as easy to shoot as the smaller chamberings, well, to be honest yes but there are other issues to deal with with such a round.

    Anyway, I guess I should qualify my comments, with conventional componants and chamberings, extreme spreads are much more critical then with some of the newer designs which are designed for one purpose, extreme range ballistic performance.

    Where conventional componants will offer vertical variation at 1000 yards in the 3/4 to 1 1/4 moa range at 1000 yards with 50 fps spreads, with the modern cutting edge wildcats and projectiles, this is cut to 1/4 to 1/2 moa vertical variation with same velocity spreads.

    I suppose thats why my thinking is the way it is, just gotten used to using these wildcats and bullets and really care very little about getting ES numbers much below 20 fps. If they are between 50 and 20 fps, I am happy and generally that load, if the rifle likes it will shoot better then I can hold out to any range I have tested to including out to 3000 yards.

    SO while ES are important, they are much more critical to some rifle combos then others.

    Kirby Allen(50)
     
  9. Boss Hoss

    Boss Hoss Well-Known Member

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    I would agree with you statements as they relate to your cannons and you have done a good job btw. My 338 Lapua AI that Speedy built (have a couple of competition barrels as well as a sporter) for me is not quite up to your speeds but agreed in the ultra high BC bullets it will be less of a factor % wise. Just that most folks shoot “normal” guns albeit I am not one of them but accuracy is my obsession and has been for quite a few years. Point is that most people who shoot the normal chamberings usually overlook the all important velocity spread.

    Speedy has developed a round called the Warp 7 and the first one chambered is on a sporter but next year a heavy gun will built to compete with it. I will be looking at the BIG 7mm pills to try in it. Right now am getting 3390 with a 150SMK but that is just a play/hunting load. The deviation for that load runs 18fps for 10 shots over the Oehler 35 and at 600 yards shoots consistent 10 shot groups of less than 3.5 inches --- lot of promise but the batch of RL 25 I am using will be depleted sooner rather than later so the next lot along with others will be used for developing the Heavy Gun loads…
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    I would agree, its a combination of many factors to get precision at long range, first and formost an accurate rifle. Second, good straight ammo with good consistant velocities and finally, a good marksmen who knows their rifle and its ballistic personality.

    Without all of these, precision long range shooting is not possible.

    Kirby Allen(50)
     
  11. Michael Eichele

    Michael Eichele Well-Known Member

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    I have found that barrel harmonics are way more important than ES in most circumstances. At least at the ranges I shoot at (1K and less, mostly between 600-800 yards). I ussually get 25-30 in the ES department. Sometimes more. A bullet and charge that the barrel likes and is in good harmony with the barrel's "node" will shoot better at long range with a 40 FPS ES than only a decent load with 20 FPS. ES certainly has it's place, but not at the expense of real good real life results. Many times I have seen a bullet's velocity higher or lower than it should be and still group well at distance.

    Hope that makes sense.
     
  12. Mikecr

    Mikecr Well-Known Member

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    The biggest single ES improvement I've ever seen, came with changing to 20' screen spacing with an Oehler.
    That dropped ~35fps to about ~8fps..

    Now I may be wrong, but that told me that ~50fps ES across a cheap chrono, might not be a problem.
     
  13. davewilson

    davewilson Well-Known Member

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    he said his crony was 10 ft in front of the barrel. might be a little close with the big boomer's.
     
  14. jeff 300

    jeff 300 Well-Known Member

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    man thinks for all the in put keep it coming. i was hoping you would jump on this Kirby be you built the rifle. I'm going to try more of the H1000 and try to get a load to group well at a 1000 before i even look at the chono this time. so 10 foot is to close? How far back should it be????? i going to load some up and try it out at 1000 this weekend.
    thank for the help
    Jeff