I have been considering having a custom load made for my .338WinMag, using Sierra's 300gr MK bullets. These bullets show a very high BC of .768 (above 2300fps). I was reading an article in Wikipedia.org about external ballistics and I came upon a section about the "magnus effect" in which the effect acts as a force acting either up or down depending on wind variable and rifling twist. The article says the magnus effect is present in rounds that have a center of pressure located ahead of the center of gravity. The article also says that longer bullets tend to show greater magnus errors due to their longer surface area that affects the flow of air around them. Do bulletmakers account for this effect? Or do they base their BC's on shape and sectional density alone?

True BC has to be shot useing 2 chronographs one in front of the muzzle and one farther away usualy 100 yards, although 300 yards is much better.

The Magnus effect will cause your bullet to drift slightly in the direction of your rifling- right drift for right hand twist. You adjust your sights to allow for it when you zero at longer ranges.

The BC may vary from one rifle to the next with the exact same bullets. The only way to determine exactly what the BC is for a bullet fired from your rifle is to test it when fired from your rifle. The difference from the manufacturer's numbers will be negligible unless your twist rate is way off for the velocity you're getting.

Calculations are fine but the only way to know for sure what a specific bullet will do out of a specific rifle is to shoot it at various ranges and under various conditions. Ballistics programs are wonderfully accurate but cannot replace field data and experience. Use the manufacturer's numbers to get an estimate and then fine-tune your data on the range.

Also be sure to look up 'spherical predecession' if you want some more reading :D

Long range shooting is a fascinating subject, and there's more to it than slinging lead downrange. It can be very critical to match up the twist rate with the bullet you are using, otherwise the high B.C. may not mean as much as you'd suspect.

And we are assuming this is for paper targets only, that is not a game bullet. Apologies if that is obvious, but we have many new shooters reading here, and they might misconstrue the purpose of such a load.

The 300 Grain SMK is used succesfuly for long range today and has been for quite sometime.
Dan Lilja has writing about this quite abit and has an article or two on his web site.

[Quote] by Dan Lilja
I've talked to quite a few hunters that have used the 300 grain Sierra .338 bullet at long-range on game like elk, deer and bears. They are reporting very good killing qualities from this bullet. The down-range energy level is tremendous.
[Quote]

http://www.riflebarrels.com/articles/longrange_shooting/shooting_hunting.htm

Many hunters have used match bullets for taking game. Still, the bullet manufacturer states rather clearly the match bullets are not meant for hunting purposes, being rather thin jacketed and explosive upon contact. I'll abide by the maker's recommendations.

Being that your interested in the subject here's a few more places for you to look. If this don't keep you busy nothing will.

http://www.long-range.com/

http://www.shooterready.com/

http://www.lazzeroni.com/ct_lrs.htm

http://www.longrangehunting.com/

http://www.snipercountry.com/

http://demigodllc.com/articles/practical-long-range-rifle-shooting-equipment/

Many hunters have used match bullets for taking game. Still, the bullet manufacturer states rather clearly the match bullets are not meant for hunting purposes, being rather thin jacketed and explosive upon contact. I'll abide by the maker's recommendations.


That's not exactly true with Sierra SMKs as the jackets are the same for the Sierra hunting bullets and the SMKs. The Berger are on the J-4 jacket and they are indee thiner than SMKs.Bergers were strickly match bullets before the sucessfull use by the Long Range hunting comunity and now Berger promotes them as hunting Bullet. Another thin Jacketed hunting bullet is the A-Max by Hornady.

As long as Sierra i selling Millions of SMK bullets to the Military they are never going to promote the SMKs as hunting bullets. The fact that the SMKs are desigbed as target bullets and that expansions was not part of the original design criterria is on of the factors that the Military use to conclude that the SMKs fit the legal definition of a FMJ. The military is fully aware that the SMK expand and or fragment on impact and they are not the first or only FMJ to do this.

The SMKs (or any of the Sierra bullets) are not my first choice for a general purpose hunting bullet because of close range shots, but as a long range hunting bullet they are excellent..

Checkout this video of a 300 grain SMK 338 Cal bullet flat a Deer at 950 Yards


http://i33.photobucket.com/albums/d62/jwp475/th_338edge.jpg (http://s33.photobucket.com/albums/d62/jwp475/?action=view&current=338edge.flv)

Yup - if you limit your "hunting" to 400 yds or more, the SMK will probably be as deadly as any softpoint hunting bullet.

Realizing you're an advocate of long range shooting, I have no quarrel with you on the issue. As you stated, the regular hunting bullets should be used by the majority of hunters, since shots most frequently taken by them are in the order of 20 to 200 yds. The occasional 300 yd shot may present itself for a good marksman.

We are in complete agreement on the subject.....