7mm STW info

Timberman · #1 11-22-2005, 09:43 AM

Hello, I'm new to this site, thought I'd ask for some advice on my new deer rifle project. I'm in the process of setting up a weatherby accumark in 7mm STW. I'm putting a Zeiss diavari 3-12X 56mm on it. Setting it up to shoot whitetails in big bean fields. Most shots average 250 yards out to about 400, don't think I'll shoot farther than that. I don't have a range longer than 100 yards to sight in on, what would be the best height to sight in at? I put it 3" over at 100 yards, figured this would be close to dead on at 300 yards. Don't have a ballistics table to go by either. I'm shooting factory loaded 140 grain winchester ballistic silvertips. Any info would be appreciated.

budlight · #2 11-22-2005, 09:51 AM

search the web for ballistic software. I have a very nice version for free.

the only problem is: Unless you chrono your loads your at the mercy of what ever they claim the speed to be.

I only shoot 175 sbt's out of my 7 stw

Timberman · #3 11-22-2005, 01:00 PM

I found a downloadable ballistics program, and entered as much info as I could. I sure don't know the ballistic coeffecient of the bullet, or the powder type winchester uses. Anyway, from what I can gather, sighted 3" high at 100 yards should put it zeroed at 335 yards. 4.4" low at 400, and 14.7" low at 500. Sound about right? Looks like I'll have to be careful at ranges from 100 to 250 yards, it says it should be 3 to 4" high along in there. Looking forward to testing it out. I'm not sure if the scope is suited to longer ranges, it has some pretty heavy cross hairs, but I'm hoping it will get me enough light to shoot the last 10 minutes at 300 yards. We'll see.

budlight · #4 11-22-2005, 01:46 PM

Most every bullet manufacturer gives the BC of every bullet they make. So just check out www.sierrbullets.com or
http://www.speer-bullets.com/default.asp?s1=7&s2=27
The powder type is not important. If i was sighting in a sub 400 yard gun and expected most shots to be @100 yards. I would go out and zero in at 100. that way you know that your nearly dead on from 0-150 yards. Then just memorize your tables for wind and drop out to 400. Then just offset your cross hairs on the target for the long shots.

Here is what they say about a 140 gr. spire point

Bullet Name Diameter inches Weight grains Sectional
.284 dia. (7mm) 140 gr. SPT .284 140 .248

Density Ballistic Coefficients

.377 @ 2400 fps and above
.386 between 2400 and 1800 fps
.400 @ 1800 fps and below

Varmint Hunter · #5 11-22-2005, 03:52 PM

The BC of the 140gr Ballistic Tip is .485. Typical velocity from the 7STW is about 3,400 ft/sec.

Given those figures, zero the rifle @ 300yds and it will be 3.2" high @ 200yds and 7.7" low @ 400yds. (For what its worth, you would be 2.6" high @ 100yds.)

A 10mph crosswind will cause 5" of diviation @ 300yds.

That should put you in the ballpark. [img]/ubbthreads/images/graemlins/wink.gif[/img]

Timberman · #6 11-23-2005, 06:09 AM

Thanks for the info. Our rifle season starts Saturday, and I'm home with a bad cold, nothing to do but watch the outdoor channel and scheme about my new rifle. Trying to get better before the weekend, got a lot of deer that need shooting. The ballistics program is pretty cool, I've been running some other calibers through it for fun. This is a good website, and I appreciate the advice.