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velocity FPS spread???????

 
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  #8  
Old 11-08-2007, 01:02 PM
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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)
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Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

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  #9  
Old 11-08-2007, 02:32 PM
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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…
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  #10  
Old 11-08-2007, 07:17 PM
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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)
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Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.

Web Page: www.apsrifles.com

allenmagnum@gmail.com
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  #11  
Old 11-08-2007, 08:06 PM
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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.
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  #12  
Old 11-08-2007, 08:20 PM
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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.
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  #13  
Old 11-08-2007, 09:59 PM
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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.
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  #14  
Old 11-09-2007, 08:56 AM
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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
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