how to reduce velocity extreme spread?

[davewilson]

at 600 it doesn't mean much. how about 1000. i ran a 180 - 308 at 2900 and 2950 and the difference is 14" at 1000 yards. there's only 3" dif at 600. most regard long range as starting in the 700 ballpark. the farther you go the more important ES becomes.

[rufous]

I would still be really interested in knowing whether or not RL25 would be a good choice for 200 grain bullets in the 300 Win Mag or would RL22 be better. If RL 22 is better why and in what way? Thanks, Brian.

[goodgrouper]

[QUOTE=boomtube;211315
Consider a 7 Mag shooting a .534 Hornady SPBT at a specific speed ( ie, not an average) of 3,100 fps and zeroed at 500 yards. That's a pretty fair long range load. Hornady's #4 book of charts says it will drop 17.1" at 600 yards. Then, at 3,000 fps (100 fps slower) the same bullet expects to drop 18.4" at 600 yards, a full 1.3" difference.

An ES of half that velocity difference (50 fps) would only cut the drop to something like 7/8"? If even if that estimation is off a half inch, it's certainly not enough to cause a miss on a 600 yd. p' dog! And all that calculating assumes zero wind and mirage to make aiming harder and assumes each bullet is cutting one hole groups out to infinity, none of which is likely in my world!

I think an accurate, reliable load with an ES of 50, varying only 25 fps from the middle speed, is a pretty good load in the real world.

Not perfect, but pretty good. [/QUOTE]



I don't mean this in a bad way but have you ever shot a load with an ES of 50 fps at 600 yards?? If you have, you did so with some bad calculations!

In your example, you zeroed the rifle at 500 yards and compared the 600 yard drop. In other words, you only have 100 yards of distance in which you are making your comparisons. Of course the difference in the two loads will be small in this small distance. What you should have done is zero them at 100 yards or 200 yards or 300 yards which is a more "real world" zero for most hunting rifles. If you would have done that, you would have seen more of a difference--something in the order of 5" to 7" depending on the bullet, bc, and conditions. That is the pure theoretical difference without the other factors that will be in your "real world" scenario. These other factors are group size, bullet stabilization (some bullets don't like being shot that extra 100 fps faster) and accuracy potential. Now consider the fact that you don't know which particular round you have grabbed from the old ammo box. Is it the slow one? Is it the fast one? Is it the one in the middle? You don't know! So supposing you play the wind, mirage, breath, heartbeat, and all the other "real world" things perfectly (which 99% of people aren't going to do on the first shot), you still have a 4" to 7" variation multiplied by two for the real world for a final group size discarding the accuracy issues at 18" to 14"!!! So, a load like that WOULD make you have a less than perfect shot an a deer's vitals at the very best! You could hit him in the brisket, the lungs, or the tuft of the backbone hair or miss him entirely!

Now for fun, let's throw in a little real world accuracy into the equation. Contrary to what I hear at the local range on a daily basis come deer season, NOT EVERY HUNTING GUN CAN PUT 5 SHOTS INTO A .1" OR .25" GROUP "ALL DAY LONG". At least mine won't anyway. The only gun I own that can do that is my 6ppc comp gun and it will only do that "all day long" if I steer the damn thing right. So we have "built in" vertical and horizontal error in our group to start that only adds to all the other stuff we've covered already! So now your guesstimated 7/8" difference at 600 yards becomes closer to "can't hit the broadside of the backside" at 600 yards. Do you see the error of thinking a high ES load will cut it for long range or even medium range?? I hope so. Please tell me there are not guys out there trying to shoot Bambi at 600 yards with guns and load that have ES's of 50 fps!!!! Screw the whales, save our poor deer!

[goodgrouper]

Originally Posted by Bruin

I would still be really interested in knowing whether or not RL25 would be a good choice for 200 grain bullets in the 300 Win Mag or would RL22 be better. If RL 22 is better why and in what way? Thanks, Brian.

Both can work. It would depend on how much case capacity I had to work with that would make the difference. If loading to fit a magazine, you would have less room to work with in which case Rl22 might be a better bet to get 100% load density whereas RL25 might be 105% or more in which case, the powder would get in the way of seating your bullets.

[rufous]

Goodgrouper, thanks for the input on RL25. My magazine box is 3.6" and my throat allows me to seat the bullets to an overall cartridge length of 3.485" with the 200 Nosler touching the lands. So if the extra 0.5 grain of Ramshot Magnum does not reduce my extreme velocity spread and give good accuracy I will probably go ahead and give RL25 a try. Brian.

[boomtube]

Goodgroup - "NOT EVERY HUNTING GUN CAN PUT 5 SHOTS INTO A .1" OR .25" GROUP "ALL DAY LONG". At least mine won't anyway. The only gun I own that can do that is my 6ppc comp gun and it will only do that "all day long" if I steer the damn thing right. So we have "built in" vertical and horizontal error in our group to start that only adds to all the other stuff we've covered already!"

You make a part of my point, at least so far as ideal, never mind field accuracy, anyway.

Understand that I didn't do my own calculations, I used a chart from a recognised ballistics authority (Hornady) to illustrate the ideal, precise effect of a 100 fps spread on a good, high speed load at 600 yards, fired with a 500 yard zero. Certainly we should all agree that such ideals are for paper and cannot be duplicated in the field, real things in the real world are likely to be much worse. I sort of interpolated a bit and made a guess of 7/8" difference as a probability of half that charted 100 fps spread. Thought I had made that clear, perhaps I didn't.

However, if you believe Hornady's long range ballistics charts are wrong, might you please explain what it is they don't understand?

[goodgrouper]

Originally Posted by boomtube

However, if you believe Hornady's long range ballistics charts are wrong, might you please explain what it is they don't understand?

There is nothing wrong with Hornady's charts. They are the same G1 drag function military ballistic charts everybody uses. The part of your equation I found wrong was what I explained in my earlier post.

#1. Your drop was figured from a 500 yard zero to 600 yards so there won't be much difference in drop between the two speeds in this short distance. In other words, you are looking at sentence in the middle of a novel and trying to guess what the book is about.

#2. Since you don't know if the round in the chamber is on the high end of the ES or the low end, or in the middle, you must multiply the drop by two for real world accuracy predictions. In other words, if your first shot went high and was the fast one of the group, you would aim lower on the next shot by the distance you shot over on the first. Then if the second shot is a slow one, you just DOUBLED your error and shot under your target. At 600 yards with the ES of 50 fps, the pure trajectory part of the equation means a tough to hit target without even factoring in all the other inaccuracies I mentioned earlier.

#3. Since bullet trajectories are not true parabolas, zeroing your rifle at the nearer half and then seeing what the drop is at the second half will be a more accurate way of comparison of two velocities.

#4. Any shooter's errors must be added to the difference of the pure exterior ballistics to make an accurate prediction of what the gun/load is capable of.

Do you understand? You looked at accurate information, you just interpreted it wrong.