I have only used the free JBM calculator, but want to purchase a good program.

My question....

Do any of the programs allow you to put in your REAL shooting Dope, found at the range, and then extrapolate the rest of the data you need from that dope, or do you just have to keep playing with the numbers until it gets close (like JBM)

I can get perfect, real live shooting dope from my rifle, say at 200,300,400,500,600, 700 and 800 yards at that days atmospheric conditions, and can get nothing that really matches in JBM, close, but it seems my rifle shoots a lot flatter in the 4,5,6, and 700 yard range of the trajectory than calculated. Then back on at 800 yards, I'm getting ready for a match to 1100 yards and do not trust the data.

Any programs that will "move" the trajectory arc around to fit real data?

Thanks,
Brad

precision shooter's workbench. Can also be put onto a PDA and used while in the field. It is the one I use and offten get first round hits at 1000 with it. Just put in all the CORRECT real time data.

How accurate it will be depends on what BC you're feeding it. If you feed JBM Bryan Litz's BC values, I think you will find JBM to be very accurate. If you're feeding it a manufacturer's published BC, it may not be.

Have a look at my report comparing 155 grain bullets. It shows how to derive a BC from your drop numbers that is specific to the calculator you are using. http://www.geocities.com/kombayotch/155_Berger_Lapua_Sierra.pdf

To be successful at this, you have to feed it accurate data (garbage in gives garbage out).

kombayotch--

Where would I find Bryan Litz's BC values, or they only for the 155's? Any real world on .308 178 A-max's around 2750fps? (And several other pills I shoot)

EXCELLENT writeup, BTW Thank you for taking the considerable time and energy to do it.

Thanks,
Brad

If your shooting Bergers, the new bc in G1 are on there website. you can pm Bryan here on the hide to get G7 bc's. I don’t have a clue if he will have bc's on other manufactures bullets. Some times you just have to keep putting in numbers until it agrees.

Assuming you have run you loads through a chronograph, use the manufactures bc as the starting point and then back down (I have yet to find one that I had to adjust up). If you don’t know your velocity it can still be done, it’s just a lot more of a hassle.

Hornady .308 178 Amax:
G1 BC = 0.469 lb/in^2 (average from 3000 fps to 1500 fps)
G7 BC = 0.240 lb/in^2 (valid for all speeds)[

Hornady advertises a G1 BC of 0.495 for this bullet. According to my measurements, the BC is actually 0.498 at 3000 fps, but falls to 0.427 at 1500 fps. For long range trajectories it's best to use the average BC.
The least error in trajectory predictions will occur if you use the G7 BC. Be sure to select G7 in JBM if you input the G7 BC.

I'm curious to know if this BC results in more accurate trajectories from JBM.
Also, how are you measuring muzzle velocity? That's an important input to the program as well.

Take care,
-Bryan

Bryan,
Do you happen to have Amax .284 162gr corrected BC's?

Hornady .284 162 Amax:
G1 BC = 0.599 lb/in^2 (average from 3000 fps to 1500 fps)
G7 BC = 0.307 lb/in^2 (valid for all speeds)

The G1 BC ranges from 0.633 at 3000 fps to 0.549 at 1500 fps. As with the 178 Amax, the advertised BC is accurate at high speed, but it's not a representative average for the bullet at long range. It's best to use the G7 BC because the velocity variation is much less.

-Bryan

Much thanks, Bryan!

i have an i phone, and even if all you have is an i pod touch the app will work. the name of it is ballistic. and i love it to death. it only cost about 4 dollars and it has everything that jbm has and also alows you to store your dope, uses the built it accelerameter in the phone to measure the angle your shooting and it even has its equivalent to a mildot master built into the app. measuring both the mil and moa retical and come ups. hope this helps out.

The program is only gonna be as accurate as the info you put into it. Horus I was told is a very good system to work off of. I was also told if all the correct info in inputed into it, its dead nuts accurate.

Bryan, Thanks for the data, I'm getting ready to get serious about this and this will be a big help. I have found a 1300 yard area I can shoot (I was previously limited to 7-800yards) I will let you know if this helps the discrepancies.

I have some reservations about my chronograph data, I have noticed discrepancies depending on the angle of the light. I am actually going to place 2 chronographs back to back on my tripod and check to see the difference in the 2 with 10 shot averages.

Another question.....I am wanting to get a new 1 in 8" twist barrel for my son's 243 WSSM (currently 1-10")just to be able to shoot some of your heavy 6mm bullets. Would you have a list of the lengths of your bullets from the bearing surface to the tip (ogive MAX length)? I will be constrained to an OA (magazine) length of 2.26" and need to know what bullets will fit my length constraints.

Thanks again for the data.
Brad

Brad,
Your efforts to measure muzzle velocity will be worth it. That's a very important number to get right.
I understand your concern about max ogive length and mag feeding. Here are some ogive lengths for some of our 6mm 'heavies':
95VLD: 0.670"
105BT: 0.649"
105VLD: 0.671"
108BT: 0.631"
115VLD:0.705"
We recommend a 1:7" twist for the 115's. The recommended twist has to work 100% of the time but you can often get away with a slower than recommended twist if you're not shooting at sea level in the winter. I've shot the 115's from my 1:8" twist 6BR with no trouble so you might consider them in your sons 243 WSSM.

One thing you can do to shorten the OAL of the loaded round is to have the chamber cut with a shorter than standard throat.
Just a consideration.

-Bryan

Thanks for the info Bryan,

Those 115's sure sound good but I don't know about getting them to fit, I've got some figuring to do. They are my "ideal" I'm going to try and build the new bbl around the best BC bullet that will fit my constraints. I'm also looking at some magazine mods that may help a little. Have you compared this bullet to the 115 DTAC's from Tubb/Sierra?

I tried your 95's and they wouldn't stabilize (in 1-10") even at 3200 fps..... they sure are pretty, though; I was really hoping they would work in this bbl. I couldn't get the accuracy out of your 90's, either. I think the throat is too long for the VLD's to work.

I ended up w/ 87 A-max's as the best balance in BC and accuracy for this bbl. It's holding .25-.50 MOA out to around 700 yards at the last F-class match he shot in.

Thanks again for all the helpful information.
Brad

Brad,
The DTAC 115's have a G1 BC of 0.540, averaged from 3000 fps to 1500 fps. Our 115 VLD's have a G1 BC of 0.551 averaged over the same speed range.
Lots of people try to get the 95 VLD's to stabilize in a 1:10" barrel with mixed results. Those who live at high enough altitude can sometimes get away with it, but otherwise performance is intermittent.
Take care,
-Bryan