On Paper Vs Ballistic Program

[s.ferg]

I realize numbers in the computer and bullet holes on paper can be way off. Kinda like theory and reality. I am shooting a Remington sendero 300 rum 6.5 x 20 long range Leupold with a gentry brake. I am loading 100.5gr retumbo w/ 180 gr accubond. I have chronographed the load at 3355fps avg. I am shooting 2.8 inches high at 100 for a 300 yard zero. Here is the problem, when I shoot the 300 yd target, I am actually 3.5 in low. My question is how do I dial up to 400 yards or further if the ballistics info is that inaccurate at close range.
I am using the shooting chrony's ballistic program. Any suggestions other than shooting and documenting the poi. at all ranges? I am limited to a 300 yard shooting range. I am new to trying to strech the range but not to shooting out past 300 yad. I just have never had the optics or a flat shooting rifle to do so.
Thanks for the responses,

Shawn

 

[Guy M]

Okay - old school solution here - I have messed around with some of the programs, and some are okay, while others seem to be very error prone. That said, I'm pretty much old-school on this one.

Feel free to disagree, but if you want to hunt game at long range, I believe you should practice at long range.

There's a whole lot more to shooting at long range than dialing in the appropriate number of "clicks" and squeezing off a round. This little thing called "wind" comes to mind, and yes, even with a rip-snorting 3300 fps .300 Rem Ultra Mag, wind plays a major role - particularly at longer ranges. Most places I've hunted out west here have some pretty significant wind on a routine basis.

So - don't limit yourself to that 300 yard range. That may be all that's convenient, but a guy can get himself somewhere to shoot some range... If a real live 600 or 1000 yard rifle range isn't handy, and I realize they're scarce in places, there are alternatives. I've set up on public land. Along power lines. With permission on private property. All kinds of ways to get 400, 500, 600+ yards.

Having been surprised a few times when real-world trajectory didn't match what ballistics tables or programs told me... Well, I'm a firm believer in actually shooting your hunting rifle to the ranges you expect to use it at in the field.

Yeah - I know - I'm an old school stick in the mud about this stuff, but I generally hit pretty darned close to where I aim. Best of luck to ya.

Regards, Guy

 

[rdc]

I am by no means an expert at long range anything. But, do you think the published BC is too good to be true? That would put you low. I think that would be the case as most BCs don't even tell you which drag table they are correcting for ie: G1, G7, Ingals, etc.

I think shooting and chronographing at long range will give you the correction factor (BC or whatever) that might get you close.

But I agree, shoot at range. I always wondered why I missed reading the wind in high power. The charts I had were off and the click values in the data books were also wrong.

Okay, experts, do you use two chronos or just move the one to different ranges and get 10 shot averages to calculate the drag?

 

[s.ferg]

I agree with the old school basics. I have decided to check the BC on the load and check several other entries on the program but when it comes down to it, I am going to physically zero at 300 then shoot at 100 then 200 to see whats going on. I guess I will need to find a location where I can shoot at 4-500 yad just to see what the drop is to at least know what the hold over is. I am actually working on this rifle for a Colorado hunt in Nov. I shoot between 200-325 yad on average for mule deer but where the elk graze are between 4-450 yds. So I am hoping to get this thing sewed up before I long.
Thanks for the replies.

 

[gonehuntinmeyer]

I echo what Guy is saying about practice but I understand wanting to know a starting point. I have found that the ballistic calculator that I use is usually pretty accurate but not perfect. When I punch in the info you provided, I get a similar trajectory to what you expected. My calculator takes into account many variables that I had to guess such as elevation, temperature, and scope height. I used my own typical number of 1000 ft. and 70 degrees with a scope height of 1.5 (low mount). I used the more conservative number from Nosler's website of 0.474 for the BC. For this set of parameters and a 300 yard zero, the 100 yard impact should be plus 2.7 inches. A better way to get started is to zero your rifle at the intended zero range and work from there. I would click up 5 clicks and double check the zero and then shoot at the other ranges. I can't explain why the actual is so different from the calculator. Just playing with other parameters to match what you observe would take some drastic changes to the velocity or BC. A velocity of 2950 and a 250 yard zero would be close. A lower BC would require a value of half or less which cannot be the case. It could be combination of things. Anyway, it is critical that you shoot a group at each range to get accurate data. Don't just shoot twice and say that it's 3.5 inches low. A MOA rifle's group at 300 yards is going to be around 3 inches. Good Luck

 

[rdc]

With your data, 350 yards shows -3.5 for a 300 yard zero. Are you sure the target is at 300 yards? Could it be 300 meters? Just a thought. I may get it wrong, but I keep thinking about it.

 

[Ridge Runner]

what you need to do is shoot at 3 known distances other than the one your zeroed at and measure your drops, then you can either tweak the BC in you computer program till the drops are correct or use a program that allows to to "figure BC from trajectory". Published BC is never dead on everywhere, you need your actual BC and then use that number in your chart, just keep all the info as accurate as you can while figuring the BC.
RR

 

[Boss Hoss]

what you need to do is shoot at 3 known distances other than the one your zeroed at and measure your drops, then you can either tweak the BC in you computer program till the drops are correct or use a program that allows to to "figure BC from trajectory". Published BC is never dead on everywhere, you need your actual BC and then use that number in your chart, just keep all the info as accurate as you can while figuring the BC.
RR

RR is right on here --- measure the trajectory and back into the numbers.

 

[davewilson]

Guy and myself must have went to the same school because i'm old and think like he does.i'm a firm believer in shooting your gun with it's preferred load at every hundred yards out as far as you will possibly shoot at game.now that i have a place to go farther, i'm gonna shoot as far as my scope will crank just for fun,rocks, groundhogs, coyotes,or anything else that might need shot at. it doesn't take that many rounds. i find a volunteer to walk and give me the impacts.as soon as i get 2 that are pretty close vertically and within a couple inches, i go to the next distance. this has a way of putting confidence in your shooting that can't be matched.scope tracking is another variable.to me, even if you have a computer, you still have to verify all the numbers before you can shoot at game. again, this means shooting at several distances to verify your gun/scope combo will hit at those distances.

 

[Rimfire]

S.ferg

Like guy said Old school or only school You NEED REAL FIRE confirmation. To combine what a few have already said not all scopes track the same true 1/4 MOA etc. not all crony's are dead acurate.

I run my numbers, print a drop chart and go to the range and get a solid 100 yard zero.Then go straight to 300, 500, and 1000 yards and and get real numbers for MOA come ups to check against the chart. Then go and tune the program to match my real numbers.

Sometimes my charts are dead on out to 600 but don't run true to 1k so there are little pen corrections with REAL FIRE confirmation at least every 100 yards.

I know it can be tough to find a place to shoot long but you have to shoot at the distance your going to hunt at and often 300 yards isn't long enough to tell you what's going on with the numbers.

As for "flat shooting" just my .02 but it's a term I dont even pay attention to. A 308 Win shoots like a rainbow but will still connect at long range, you dont need fps to be accurate with a good proven set up.

I think once you get things worked out you will quickly meet your goal. Good luck in Nov.

PS make a log and keep good notes on each outing.

 

[Ridge Runner]

Sure you always confirm your chart at different ranges. I thought that was a given.
RR

 

[mikebob]

JBM - Calculations - Trajectory (Basic) is a pretty close program that will get you on target. You will still have to tweak it but it will get you close enough to be on the target. Save some rounds and waiting for bbl to cool down. I zero at 100 then 500 and 1000, then tweak bc until all match. Print it and go shoot the middles to make sure they match. JBM is a great program for free online and wil even print cards. That web sight has alot of good stuff you should check it out.

 

[s.ferg]

Well I shot today . The 100.5 gr shoots good at 100 but out at 300 very unstable shooting irratic probally the excessive pressure as someone spoke of due to the longer accubond bullet. When I changed to a 99.0 gr load which shot as good as the 100.5 max load , Without moving the scope, the first shot was dead 0 and 2.0"r windage at 300, the second shot was at the 2.25"r windage but 1.5 high, I pulled the third way low guess I flintched. I let it sit for about 15 minutes and shot two other guns. When I shot the 4th shot, It was 1.5" high at 1.5r windage. So the center of my group is +1" ^ and 2" right.I going to shoot again tomorrow or Saturday waiting long enough to shoot 3 out of a cold barrel. I do not understand why the max load that shot good at 100 would be so irradic when shooting .3xx Well I am going to get it shooting at 300, then shoot at 200 and note my height, then at 100, maybe I found the pill for the ailment. I guess it's trial and error. Thanks all for the replies. Your ideas and input have given me a lot to consider, I'll keep you up to speed with my progress.
Shawn

 

[Ridge Runner]

what did your groups measure at 100?
what twist ya have?
how many shots did you chrony? (shots in succession unless you let it completely cool get slower.
RR
Here's 2 shots dialed up from a 100 yard zero (the first attemt at long range dialing) at 660 yards in an 11mph crosswind

This was before tweaking my BC in my ballistic program