going from 600 to 800 yards

[rufous]

I would like to extend my effective kill range from 600 yards to 800 yards. I feel confident at 600 at this point but have not shot much past that with my 300 Win Mag. I did shoot once at 1000 yards and got an 8" three shot group. This load typically gives me sub 2" groups at 250 yards.

In looking at a ballistic program I see that temperature, elevation and velocity make a significant difference at 800 yards but not so big a difference at 600 yards. I was surprised to see that temperature made a difference. I would have figured that it would not matter what the temperature was. Why/how does it affect trajectory?

My load is using the Barnes 180 TSX at approximately 3070 fps. The problem is that sometimes the velocity is 3090 and sometimes it is 3030, depending on temperature and who knows what else (I am using RL22, perhaps I should be using H4831 which supposedly is less sensitive to changes in temperature). I have a Leupold 3.5-10 with the Boone and Crockett reticle and would plan on using the 500 yard aim point and then dialing in the needed extra elevation on the scope to be rezeroed at longer range.

The worst case scenario difference in trajectory at 600 yards with velocity at 3030 fps, temperature at 30 degrees and elevation at 3000' compared to velocity at 3090 fps, temperature at 80 degrees and elevation at 6500' is only 2" but at 800 yards there is a whopping 16" more drop (again from a 500 yard zero) at the slower velocity, lower elevation and lower temperature.

So how do you guys account for all of these variables in the field, especially not knowing exactly what your velocity is going to be on any given shot? What do I need to do to take the next step in long range hunting? Thanks so much, Brian.

 

[royinidaho]

Number 1 item would be to get those extreme velocity spreads down to no more than 15 FPS over a bunch of shots. ES less than 10 is 4 times better and about 20 times harder to achieve. Reach your own personal balance but what your experiencing at this point won't cut the mustard.

Your catridge is definitely good for 1000 but the vertical stringing will drive you nuts.

You may with to try a heavier bullet and slower powder. You may well end up with a summer and winter load. A lot of people do that.

 

[rufous]

My extreme spreads are not usually that great. I did not mean to say that on any given outing that I will get velocities ranging from 3030 to 3090 fps but that on cold days I get lower velocities than on hot days. Even so how does one reduce the extreme spread? I measure each powder charge on an electronic scale so that every one weighs exactly the same (to the nearest 0.1 grain) and use Federal Match primers. What else can I do to ensure the smallest extreme spreads? Thanks, Brian.

 

[Buffalobob]

Ok Rufous, I will let other deal with ES being as I don't know anything about it and I will just give you a basic course in long range trajectory.

You should go out and dial your gun in for what ever range you would like to shoot and then for a couple of hundred yards more. So if you wanted to shoot tadpoles out to 1000 yards you would have a dial in to 1200 yards. If you want to shoot possums at 800 yards you should dial in to 1000 yards.

The dialin should begin at some recognizable point – say 100 yards for a beginner and you should shoot the gun into the target for every two hundred yards out to 1200 yards. Typically I shoot a group at a distance and then fine adjust and reshoot to verify the adjustment and then move on to the next distance. Close in such as 100, 300 and 500 yds I may only shoot 1 or two rounds as a group and as the distance increases I will increase the number of bullets in the group.

The barrel must be kept cool during all of this shooting and somewhat clean. The temperature should be not freezing cold nor blazing hot. Wind should be almost none. I try to start shooting at first light and really don't like to shoot once the sun gets on the target because I have trouble judging mirage. This means several sessions to get a good bullet dialin. All of the bullets should be from the same loading so there is nothing different in the cartridges.

No then, you should have a notebook of some kind and in that you will record the drops for every distance you shot. This is critical that you keep this information in a safe place so you can get at it again.

If you have a chronograph, that is great. If it is accurate that is even better. If you trust what it says, you shouldn't. You now have a muzzle velocity and six or seven drops along the trajectory of the bullet. You have the manufacturers Ballistic Coefficient. In a perfect world you could simply take a ballistic program and input the muzzle velocity, BC, temperature, altitude and other data and the program would compute a trajectory that would match the drops you shot. It is unlikely that your real world data will match the data from the computer. So at this time you must start a guessing game. If you adjust the bullet BC to a lower value then the drops will increase. If you adjust it to a higher value drops will decrease. What I expect you will find is that you cannot match your real data by adjusting only the BC. You should then begin tweaking the muzzle velocity at BC values that were close to your real data. Remember that it is more important to match the further out data points than the closer data points if you are shooting at an animal. This is why you shoot way past where you plan of shooting an animal – to make the longer range part of the curve more accurate. Once you have a good match to your real data you print out what you have. What you print out must have the final muzzle velocity and final BC you used to duplicate the curve.

So you now have a drop chart but you get tired of shooting Walla Walla bingbangs and decide to go to Colorado and hunt up high in the snow. Take you computer and the information that produced your drop chart and change only temperature and elevation. Do not change BC nor the input muzzle velocity (I don't care what the "real" muzzle velocity is). This will shift the shape of the trajectory by only the factors that have physically changed.

Finally, when you get to Colorado up in the snow, verify your zero and verify at least one drop at a long distance. If they don't match than adjust your drop chart again.

In all of this you should see that I give preference to what I see my bullets do. Every time, I will believe my bullets over my computer or any other electronic device. Bullets kill elk, computers kill time.

 

[goodgrouper]

[ QUOTE ]
Even so how does one reduce the extreme spread? I measure each powder charge on an electronic scale so that every one weighs exactly the same (to the nearest 0.1 grain) and use Federal Match primers. What else can I do to ensure the smallest extreme spreads? Thanks

[/ QUOTE ]

Brian,
Even if you have the powder charge measured out to the very last kernel exactly, some powders and/or charges will never give good extreme spreads. You can only work up each load over a chronograph and "map" the powder you are using to find accuracy/combustion nodes that yeild small spreads.

Some loads might have a standard deviation (I'll use this from now on because it is a little more accurate than using extreme spreads) in the single digits but produce horrific groups. ANd some loads have razor edge accuracy but horrible standard deviations. The trick is finding a load that has good accuracy and good deviations. Once this has been tested a few times and the accuracy and uniformity have remained the same, you will have found the optimum load for your particular components and rifle. Now you can change the temperature 40 degrees or so and the load will usually hold onto it's uniformity and accuracy even if the overall speed increases or decreases.

SO, now it is 50 degrees colder than when you worked up the load. So we go out and check it again over the chrono a week or so before your hunt so the temps will be similiar and refigure our charts for the velocity change and do any final tweaking.

However, a good portion of guns/cartidge combos will totally change their accuracy and deviation nodes in temperature changes. If your gun is one of these, than count yourself among the unlucky. This is not a huge probelm, it just means that you will have to have a summer and a winter load. And if your gun is really picky, you might have to have a spring and fall load as well. So this means you will be finding two or three or four accuracy nodes on the same gun. Count on spending lots of time shooting over the chrono in this case!

Hope this helps.

 

[Chawlston]

Hello,

I agree with GG again. What I do for my barrels that I load for is to find the max charge in the warm weather with the bullet touching the lands and then back off one grain. This is now my maximum charge period! Next, I start seating groups of bullets .010" deeper into the case and shoot them for accuracy and velocity deviation. Most of the time, I find the most accurate groups also have the least velocity deviation.

My above procedure works for me and I started using it becasue I have so many chamberings I load for and cannot invest time to test every bullet, powder and seating depth combination. Anyway, if you cannot find the node where accuracy and velocity deviations are satisfactory, it is time to change powders and do it all over again. With a little experience and some wisdom from people who use your caliber, you will find it much easier to get to the magic loading for your gun. Also, make sure you are using a mirage shade as this help prevent heat waves off the barrel from changing your sight picture. A venetian blind velcroed to the barrel is what works for me. Good luck.

James