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]

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 **** 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]

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 **** 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]

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.

 

[boomtube]

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

Ah. Now I understand. I guess.

You are saying that there are mulitple ways of "interpeteding" a ballistics chart and I thought I was only reading what Hornady says about drop variations at 600 yards due to 100 fps speed differences. Silly ol' me.

Okay, I don't mind saying it, you win!

 

[AlbertaAl]

I'm a little late chiming in here but I reloaded extensivley for a 300 Win Mag
in a SAKO factory model 75 rifle.

Best load was using:
BERGER 210 seated 4 thou from rifling
LAPUA brass, Federal 210 match Gold Medal primers,
80.0 grains H1000
avg 2853 fps ES 35.67 / SD 13.11
3/8" group @ 100 yds.

Hope this might help your situation in some way !

Regards
AL

 

[Boss Hoss]

Just to put this to bed hopefully --- I compete at 1K won my share and will tell you that ES is CRITICAL at 1K period end of story. On a competition rifle it will make the difference between winning and not even being in the running or worse yet a DQ. On a long range hunting rifle it makes the variables that you do not have to worry about on a competition rifle become painfully obvious. Vertical dispersion is a killer.

 

[PDA]

I thought the primer could have a big effect on ES? Am I wrong? It seems so since no one has suggested trying another primer. What about a CCI250 or BR2? Someone more knowledgeable please advise.

 

[coues7]

Very good thread!

 

[AtownBcat]

Just got my first chrono...Would someone please take a sec and explain ES and SD? Thanks

 

[Jamie6.5]

ES = Extreme spread. The maximum velocity variation with a given load.
The highest velocity minus lowest velocity equals ES.

SD= Standard deviation. The average velocity variation of a given load.
Subtract the lowest velocity from all others in a batch of a given load. Add those differences together and divide by the number of shots.