Range Report JBM Ballistic Calculator

[TT]

Just a quick review.

Recently used it to create some data cards. Excellent tool, very user friendly.

Selected the off-the-shelf Sierra data for the 30 cal. 175 MatchKing 300 yard zero with 2750 ft/s MV.

Calculator stated 15.9 MOA drop to 750 yards and 23.3 MOA drop to 900 yards.

Set up LV Steel 10.25x17 target and 750 yards, dialed in 15.75 MOA and and hit the target (right bullet mark) on the second shot.

Moved the target out to 900 yards dialed in 23.25 MOA and hit the target (left bullet mark) on third shot.

Not sure why the Litz data is different, as I will be using the Sierra provided data...


http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

 

[azimutha]

Re: JBM Ballistic Calculator

Sounds like you got good results with the Sierra data. You might try the Litz data for comparison. It comes from his book - Applied Ballistics for the Long Distance Shooter - and was gleaned from very accurate tests. I've found that with other bullets, his BCs are much more realistic. Not having the book with me I can't compare it to Sierra's published figures.

 

[jrob300]

Re: JBM Ballistic Calculator

Once you get out past 1000 yds., you'll find data like Litz's, as well as G7 BC's to be more accurate. They take into account the changing G1 BC with slowing velocity.

John

 

[TT]

Re: JBM Ballistic Calculator

John - thanks for the heads up. To be honest with you it seems difficult enough shooting the 308 accurately at 900 yards. So much so I have a 30-06 build in progress and plan to use the 208 AMAX as an improved countermeasure to the wind.

Are you of the same opinion regarding the Litz data for the 208 AMAX?

Kindly advise...

 

[jrob300]

Re: JBM Ballistic Calculator

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TT</div><div class="ubbcode-body">John - thanks for the heads up. To be honest with you it seems difficult enough shooting the 308 accurately at 900 yards. So much so I have a 30-06 build in progress and plan to use the 208 AMAX as an improved countermeasure to the wind.

Are you of the same opinion regarding the Litz data for the 208 AMAX?

Kindly advise... </div></div>

Velocity, it seems, trumps BC. Depending on what you get out of your 30-06, it may or may not mean that much, again depending on what range you shoot at. I've found Litz's data to be more important after 1500 where bullets are starting to auger.

PM Bohem here on the Hide. He's getting 2900 fps from 208's in a 30-06. He may be able to steer you in a good direction.

John

 

[TT]

Re: JBM Ballistic Calculator

"Velocity, it seems, trumps BC. Depending on what you get out of your 30-06, it may or may not mean that much, again depending on what range you shoot at."

While I agree regarding the vertical component of the velocity vector (where drop is a function of time) - I believe the data shows ~33% less windage required for the 208 AMAX given the same muzzle velocity (which relates the horizontal component of the velocity vector in the y-axis shown below). That is really what I'm trying to accomplish. Calling wind at 900 yards (or further) with no flags etc. is very difficult...

 

[jrob300]

Re: JBM Ballistic Calculator

I honestly don't remember where I was going with the velocity thing... old age.. and I totally missed the wind reference.

So, to answer your question, I think... my real world wind numbers don't jive with the numbers I get from JBM no matter whose BC I enter. In practice, I'm correcting just over half what it calls for.

These bullets truly are amazing. My shooting partner shoots 200 SMK's at 3000 fps and I had him holding almost a mil and a half for a 5 mph full-value wind at 1500 whereas I could hold just left of the 24" plate and hit center mass. It's hard to know if the conditions were exact, but to my eye they weren't noticeably different.

John