Bullet drop-39gr Sierra

WyoWindage · Post by **WyoWindage** » Sat Feb 02, 2013 3:31 pm

Just shot a match today. Wasn't aware of format, yardages, etc. so didn't get to sight in earlier. Shot 10 at 200yds, then 5 at 400 yds, then 5 at 100yds. I was set up for 200yds so didn't do too bad. At 400 yds, I shot about 12 rounds, with aim point from 30" hi to 4" hi, and couldn't see any holes in target. When they came in, I had 5 on paper (about 2ft square). Looking at ballistic tables here at home, Accurate Shooter shows about 17" drop from 100yd to 400yd (Sierra 39gr BK). Then JBM Ballistics shows almost double that drop at 400yds (about 36"). I know I am not looking at these tables right, but need some help to get me on track for test trip and next match. No wind flags or sighters allowed

. Thanks for any tips. Ron.

TC Encore204 · Post by **TC Encore204** » Sat Feb 02, 2013 4:35 pm

What kind of velocity are you pushing the bullets? My ballistic calculator shows a 39 BK at 3570fps dropping 16 inches at 400 if zeroed for 200. That's at sea level 59 degrees.

WyoWindage · Post by **WyoWindage** » Sat Feb 02, 2013 4:57 pm

Suppose I'm in that ballpark, maybe 3700fps, 25.5gr v133.

Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
0 -1.5 *** 0.0 *** 3000.0 2.687 779.2 0.000 0.0 ***
100 -0.0 -0.0 1.3 1.2 2608.0 2.336 588.9 0.107 18.9 18.0
200 -3.7 -1.7 5.5 2.6 2226.4 1.994 429.2 0.231 40.7 19.5
300 -14.4 -4.6 14.0 4.5 1845.9 1.653 295.0 0.379 66.8 21.3
400 -35.6 -8.5 28.0 6.7 1513.2 1.355 198.2 0.559 98.4 23.5
500 -72.1 -13.8 49.0 9.4 1245.9 1.116 134.4 0.778 137.0 26.2

This is JBM, shows 35.6" at 400yds, I think?? The Sierra figures are 17.06" drop at 400yds from 100yd zero. This sounds more reasonable than 35.6"?

HeadLever · Post by **HeadLever** » Sat Feb 02, 2013 7:50 pm

Be aware that the Sierra 39gr listed BC is a G1 number, which is NOT the best model to be used for modern boattail bullets. If you look deeper, you will see that the listed G1 BC for this bullet is dependent upon velocity. The G7 model would be much better suited, but unfortunately, I don't think that they have a published G7 coefficient.

If you are shooting at extended ranges where the velocity is much lower, you will see a deterioration in the G1 BC as well. In order to take out much of this guesswork, I would suggest shooting the rifle at multiple ranges (while keeping good notes on the conditions at the time) and developing a good chart from how you gun actually shoots.

Of course this could be quite a bit of work, but hey; more excuses to get out and spend time behind a rifle!

TC Encore204 · Post by **TC Encore204** » Sat Feb 02, 2013 9:05 pm

Looks like you only have 3000 fps as the muzzle velocity.

WyoWindage · Post by **WyoWindage** » Sat Feb 02, 2013 9:44 pm

Calculated Table
Range Drop Drop Windage Windage Velocity Mach Energy Time Lead Lead
(yd) (in) (MOA) (in) (MOA) (ft/s) (none) (ft•lbs) (s) (in) (MOA)
0 -1.5 *** 0.0 *** 3700.0 3.314 1185.3 0.000 0.0 ***
100 -0.0 -0.0 0.7 0.7 3351.0 3.002 972.3 0.085 15.0 14.3
200 -1.6 -0.8 3.1 1.5 3008.2 2.694 783.5 0.180 31.6 15.1
300 -7.1 -2.3 7.4 2.3 2682.2 2.402 622.9 0.285 50.2 16.0
400 -17.4 -4.2 14.1 3.4 2364.0 2.117 483.9 0.404 71.2 17.0

EUREKA; That did it, now at -17.4". I didn't input the correct velocity. Will be testing later. Now if I can see my bullet holes. Thanks, Ron.

TC Encore204 · Post by **TC Encore204** » Sat Feb 02, 2013 11:09 pm

I just got a new calculator that allows different BCs for different velocities and here's what it came up with:

Range(yd). Path(in) Path(moa) Drift. Drift Velocity Energy TOF(s)
400 -19.2. U4.6 -0.0 0.0 2133.4 394.1 0.424
350 -12.6. U3.4 -0.0 0.0 2325.5 468.3 0.357
300 -7.7 U2.4 -0.0 0.0 2507.9 544.6 0.295
250 -4.1 U1.6 -0.0 0.0 2700.0 631.3 0.237
200 -1.7 U0.8 -0.0 0.0 2891.4 724.0 0.183
150 -0.4 U0.3 -0.0 0.0 3084.0 823.6 0.133
100 0.0 0.0 -0.0 0.0 3288.2 936.3 0.086
50 -0.4 U0.7 -0.0 0.0 3493.7 1056.9 0.042
0 -1.5 0.0 -0.0 0.0 3700.0. 1185.5 0.000

WyoWindage · Post by **WyoWindage** » Sun Feb 03, 2013 10:59 am

A bit more drop. I think

I can handle the scope turrets now, and not hold off. A Simmons Whitetail Classic, 1/4" clicks. On 100yd at zero, up 1.6" (3 clicks) at 200yds, then up 17" (4 clicks) at 400yds. Does this sound close? Thanks again. Ron.

TC Encore204 · Post by **TC Encore204** » Sun Feb 03, 2013 2:59 pm

1/4 inch clicks at 100 are 1/2" at 200, 3/4" at 300, and 1 inch at 400. So your figuring for 200 is about right but at 400 since you need 17 inches it would be 17 clicks.

WyoWindage · Post by **WyoWindage** » Sun Feb 03, 2013 4:39 pm

Beginning to understand why my math teacher

when I turned in my homework. Thank you very much TC. Ron.

TC Encore204 · Post by **TC Encore204** » Sun Feb 03, 2013 10:39 pm

No problem, that's what this place is for. My dad and I are always talking about ballistics, and I read a very in depth book about it by a Phd, otherwise I of been in the same boat as you lol. Good luck in your next match.