"Point Blank" Ballistic Programs?

[Nicholas]

I am using the Point Blank Ballistic program to calculate the ballistics for my 308 win.

With the conditions I'm shooting under then the program says I need 38 moa to be zeroed @ 1000 yards from my 100 yard zero. But I actually need 42.5 moa. Is this amount of error typical of Ballistic programs?

Here's my data if someone would please verify it on another program for me:

175 grain Matchking BC=.496
Velocity is 2640-50 fps
elevation is 5000 ft above sea level
temperature is 90 degrees
scope height is 1.5 inches

The reason I am asking is because I was rereading Blaine Fields post "Why a Knowledge of Ballistics" where his 1 in 12 twist barrel was having issues with the heavier projectiles at 1000 yards. I was able to consistantly hit at 1000 yards so I don't think my 1 in 12 barrel is having problems, but I thought I'd ask anyway.

What you also need to factor in is the Rel Humidity and Bar. Pressure at altitude....

Here's what I got...

@ 2645 average vel.

@1000 yards with 90 degrees 5000 ft Ele. 30.17 Bar. Pres. ( thats what it said for yesterday ) 38% rel. Hum. Shooting the 175 SMK.

@1K .....
1468 FPS
838 Ft. Lbs.
-333.64 inches
Almost 37 MOA

All I can say is .. are you sure your velocity is 2645 ish

if your at 2600 that is about 42 MOA... ???

[ 09-15-2002: Message edited by: *WyoWhisper* ]

[Nicholas]

I chronoed the load two months ago, though it was warmer back then so many I'll chrono them again.

At 500 yards I need 1 moa less than what Point Bland says.

Thanks

[Tim Behle]

I've had real good luck with Point Blank. I enter all of the information for each shot during load development, and a gain for each shot for several groups. For most of my loads, it has been right on the money all of the way out to 1,000 yards.

The biggest problem I've had is due to the temperature swings we have here. If you use a drop chart developed for a 70 degree morning, you will over shoot a coyote during the 95 degree afternoon.

If i shoot in 90 degreees I loose 30 - 40 fps in 70 degrees..

bet that may be the culprit....

[waitaminit]

Somewhere in PS I read an article named 2Why BC is BS".
I think the author knows why he used this title.

The Sierra Manual lists a BC of .496 for a speed between 2800 and 1800 fps and hops to a BC of .505 for more than 2800. As there is no stepwise increment in BC, one can expect a BC of more than .5 for 2650 fps.
Your experience shows the opposite.
A while ago, I talked to a Sierra technician who said they do tests up to 200 yrd, so I wonder from where they know about the long range performance of their bullets.

When I use your data in the Perry software, the results are close to yours (378" drop) while Sierra's rangetable shows a drop of about 436".

You may need to correct the optimistc Sierra BS-BC, I'm afraid.

[Nicholas]

I hope that is what it is. The next thing I am going to test is the Elevation turret values on my scope to make sure they are what they say.