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velocity FPS spread???????

 
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  #1  
Old 11-07-2007, 09:35 AM
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velocity FPS spread???????

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?
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  #2  
Old 11-07-2007, 11:22 AM
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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..
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Old 11-07-2007, 02:01 PM
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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.
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Old 11-07-2007, 07:01 PM
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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
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Old 11-07-2007, 08:47 PM
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Quote:
Originally Posted by jeff 300 View Post
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.

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
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Old 11-08-2007, 12:11 AM
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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)
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  #7  
Old 11-08-2007, 10:30 AM
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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…
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