Sighting in rifles for long-range match - need some help with ballistics

[Kabal]

I'm going to participate in a match that includes some long(ish)-range shooting (200 and 475 m = 220 and 520 yards). I'll only get 5 sighting shots per distance, and I only have a 100 m (110 yards) range available to sight in my rifles before the match, so I'll have to do some maths.

It would be great if you could check if my approach is reasonable, and help me out with some details.

Let's take the 520 yd match as an example. I am using the ballistic calculator from gundata.org: http://gundata.org/ballistic-calculator/
I set "zero range" to 520 yd and calculated the "drop" of the bullet at 110 yd. It gives me a "drop" (i.e. rise) of about +11.8" at 110 yd.

Now I should be able to sight in my rifle for the 520 yd match using the 110 yd shooting range by making sure that my rifle shoots 11.8" above point of aim – correct?



As for the details:
For the 520 yd match, I will be using a scoped Izhmash Tigr rifle chambered in .308 Win (22 ¼" barrel; 3.3" sight height over bore; shooting S&B 147gr FMJ factory ammo).
Gundata.org gives a ballistic coefficient of 0.409 for the S&B bullet, and I estimate that muzzle velocity is around 2800 fps. According to the ballistic calculator, this results in a 11.8" rise at 110 yd, as mentioned above.

I'd like to compete in the 220 yd match with a Swedish Mauser m/1896 chambered in 6.5x55 (29.1“ barrel, 0.7" sight height over bore, shooting S&B 140 gr FMJ factory ammo).
According to gundata.org, the bullet's ballistic coefficient is 0.465, and muzzle velocity for S&B 140 gr FMJ ammo is 2582 fps. This should result in a 3.2" rise at 110 yd.


Some additional, not so decisive questions:

- Do you think 2582 fps is a realistic muzzle velocity for a 147gr FMJ bullet out of an M96 Swedish Mauser?
The S&B homepage specifies that this velocity is achieved trough a 24" barrel (a little longer than an M38 barrel). Might the barrel of the M96, which is more than 5 inches longer, lead to a significantly higher muzzle velocity?

- Am I correct in assuming that the G1 drag model is the one best suited to calculate the trajectory of both the .308 and 6.5x55 FMJ bullets used by S&B?

Thanks for your help.


And now, after so many numbers, it's time for some pictures:

 

[taliv]

Well that's totally backwards but it just migh work. I'm posting from an iPhone so I will be brief. Normally you zero at 100 and then just let the calculator build a range card for all ranges. The calc will tell you how many minutes or mils you dial on your scope to hit the target at the cooresponding range.

If your numbers are right and I'm understanding you correctly you've essentially figured out you have to come up 11.8" at 100 to hit 520 or whatever. What you should do is leave your rifle zeroed at 100 and convert 11.8" to moa or mils (it should be about 11 minutes or 3.x mils)

 

[Dave P]

If you are zeroed for 100 meters, click up 3 minutes and you will be very close for 200 meters.

 

[Kabal]

Thanks for the advice, taliv and Dave!

Unfortunately, this won't work for the Swedish Mauser, as I'll have to shoot with factory iron sights.

As for the scoped rifle, I was aware of the option - I was just not sure if the MOA adjustment on the scope (Nikon Fieldmaster) is as precise as the (admittedly complicated) solution I came up with.

Gotta go now, but I'll think about it and post again later.


Edit: I'll just zero the Tigr at 100 m, click up 11 or so minutes on the scope, and check if this results in the 11.8" rise I predicted.

 

[jerkface11]

Don't put too much faith in that 11.8 figure. Since you don't know the actual velocity you're point of impact won't be where the calculator says. That number should get you close though.

 

[Float Pilot]

I compete with a m/96 Swedish Mauser ( Deutsch gemacht, 1900 Oberndorf ) and a m/38 Husqvarna Swedish rifle.

I replaced the front sight blade with a taller blade and filed it down until it was correct for 100 meters using my best hand-loads. I was able to figure my various sight settings for longer ranges after chronographing my loads.

If I had some S and B ammo I would chronograph it for you...But I never found their ammo to be very accurate so I do not keep any around the shop.

 

[mnhntr]

S&B 147gr on my ballistics calc shows 2808 out of a 26in barrel. And a rise of 12.2in at 100yds if sighted at 500yds

 

[Kabal]

I somehow missed your posts, Float Pilot and mnhntr. Thanks for the help!


A little post-match report:

Jerkface11 was right - you shouldn't put too much faith in ballistic calculators. A few days before the match, I adjusted my Swedish Mauser's sights so it shot 3.2" high at 100 m.

However, when I fired my test shots before the actual match, all the shots went high at 200 m (by what looked like 2.5 - 3" on the screen of the electronic scoring system).
Looks like the round's trajectory is so flat there's barely any difference between 100 and 200 m. Another shooter who also used an M96 and S&B FMJ ammo confirmed this.

Well, I aimed a little lower and still won the match. But I also learned something on ballistics that day.


The 500m match with the Tigr didn't turn out that well.
One of the screws that hold the picatinny rail to the sidemount worked loose during shooting, causing the scope to wobble around - which I only noticed after the match.
I still got a few rounds on paper, inclunding two lucky 10s.

I had checked the fit of the sidemount and the tightness of every screw on the scope rings before the match. I wasn't even aware of that particular screw which failed me. Another lesson learned, I guess.

 

[taliv]

congrats on the win!

Looks like the round's trajectory is so flat there's barely any difference between 100 and 200 m

well, that's true of just about any rifle cartridge from 223 to 50bmg if by "barely" you mean about .3 mil
if you mean less than .3 mil, then it's likely your height over bore wasn't input correctly.

 

[Kabal]

Thank you!

well, that's true of just about any rifle cartridge from 223 to 50bmg if by "barely" you mean about .3 mil
if you mean less than .3 mil, then it's likely your height over bore wasn't input correctly.

It looked like a little less, but I'm not sure because I only had a computer screen that showed me the hits, and I don't know exactly how big the target was. There might also have been other factors involved. I zeroed the rifle at an indoor range from a sitting position, but I shot the match in broad daylight and from a prone position. Maybe the difference in lighting affected my sight picture.

Anyway, the bullet didn't seem to drop quite as far as the ballistic calculators suggested.

 

[taliv]

lights up, sights up!

 

[dprice3844444]

buy a good chronograph to work up your loads and bullet drop.

 

[hvychev77]

Check out jbm ballistics website to get your adjustments. It's been helpful for me. Keep in mind though, garbage in = garbage out.

 

[mnhntr]

Ballistic calculators work but the info we gave you was with our current weather and elevation ect. The best results are with the right info and it all adds up. Congrats on the win!