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BC Question .30 vs. .33 cal

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Unread 05-21-2007, 05:27 PM
Bronze Member
Join Date: Oct 2006
Location: South Jordan, Utah
Posts: 73
BC Question .30 vs. .33 cal

A friend and I were talking the other day about BC's on the .33 and the .30 cal. He was telling me that:

"the 240 gr .308 and 250 gr.338, the .308 still exhibits a higher bc in all makes of bullets I know of. Until the 300 gr Matchking, which obviously is not available in .308, the .30 cal bc,s tend to run higher than that of the .338. And I wouldn't reccomend an SMK for hunting, but that is another story. Not trying to pick a fight, if I am wrong, I would like to know."

I have always been under the impression that the .33 had higher BC's with heavier bullets than the .30. Am I wrong? Can you guys please explain this to me. My friend and I are always up for learning so maybe you guys can help us out. Thanks in advance.
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Unread 05-21-2007, 06:35 PM
Gold Member
Join Date: Sep 2005
Posts: 748
Re: BC Question .30 vs. .33 cal

Hi if you have a smaler diameter projectile weighing the same as a larged diameter projectile and they are both of the same type EG MatchKings the smaler diameter projectile will have a higher BC. Now that sounds great in practice but with the same case eg a 300 Ultra mag with a 240gr Matchking will not push it out as fast as a 338-300 Ultra mag so the larger diameter one will beet the smaler one in velocity. The next thing you do is use a larger weight projectile in the larger diameter projectile so the 300gr MatchKings come into question. When you increase the weight and diameter generaly you get a higher BC combination. The other thing is retained energy as you go up to the larger projectiles they retain a lot more of it to make sure you have enough energy to get the job done.

You have to compare apples to apples here you cant compare say a 300 ultra mag with 240gr MatchKings to a custom 270 with 195gr Wildcat ULD's and a non factory twist you have to compare conventional twists and projectiles against each other and the wildcats against each other aswell.

Now all that has been said what do you want to do? A 300 Ultra mAg is a good long range rifle loaded with the 240gr Sierra MAtchKings but the 338-300 Ultra Mag loaded with the 300gr Sierra MatchKing is even better (338 Edge)

Cheers Bill
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Unread 05-22-2007, 08:44 AM
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Join Date: Jun 2004
Location: Fort Shaw, Montana
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Re: BC Question .30 vs. .33 cal

Comparing bullet weights in different calibers concerning BC will get you into some trouble unless you have a basic understanding of a few things.

The most important thing to compare is sectional density when comparing different caliber bullets. Sectional Density is basically the ratio of bullet weight to bore diameter to greatly simplify things. This allows you to compare bullets of different calibers that will have similiar terminal performance when they are made of the same similiar design.

If you look at sectional density of 30 cal and 338 bullets, this is what you find:

30 cal
200 gr..........0.301
220 gr..........0.331
240 gr..........0.361

338 Cal.
225 gr..........0.281
250 gr..........0.313
300 gr..........0.375

Looking at these numbers it allows you to group the 30 cal and 338 cal bullets with similiar SDs and compare them to get a more accurate idea which bullets should be compared to which bullets.

Its hard to compare 240 gr 30 cal SMK to a 250 gr 338 cal bullet. As has been mentioned, this is an apples and oranges comparision. If you look at the sectional density of the above bullets you see that a 240 gr 30 cal has a sectional density much closer to the 300 gr 338 cal bullet then any other on the list so those two should be compared and in that case the 300 gr SMK has the advantage in ballistic performance.

Bullet design can also play a huge role in ballistic performance however. If you take for example some of the new Wildcat Bullets Aluminum tipped bullets that weight 266 grains in 338 cal and compare them to a 338 300 gr SMK, we see the above idea does not hold true because of the different design of the two bullets.

The lighter bullet has a much lower sectional density of around .333 compared to .375 for the 300 gr SMK. But, the tipped bullet is significantly longer then the 300 gr SMK because the aluminum tip allows a longer bullet with less weight then an all lead bullet.

In this case, the expected BC of the new Wildcat Bullet will be in the .850 range at least compared to the SMK which has a BC of .780 in most cases.

If you compare the new Wildcat 266 gr 338 bullet to the closest 30 cal bullet as far as sectional density, that is the 220 gr SMK.

With these two bullets you are comparing bullets with basically identical section densities, 0.331 vs 0.333, for all intent and purpose, identical. If you look at BC, the 220 gr SMK will have a BC in the 0.630 range according to Sierra, again, the 266 gr 338 tipped bullet will be in the .850 range.

Comparing different caliber bullets is a tricky business. It is hard to say that a smaller caliber will offer higher BC then a larger caliber or vice versa for that matter. If has more to do with bullet design then anything else.

Using sectional density allows you to compare bullets that are in the same class and will generally provide similiar velocity potentials when used with similiar case capacity cartridges. For instance, a 30 cal bullet with a SD of .333 will be driven to similiar velocities as a 338 cal bullet with the same SD when both are using the same powder capacity.

Not this is not exact and other variables come into play here as well but its close.

So I will not say your friend comments are incorrect, just that they need to be qualified a bit. It is true most conventional weight 30 cal bullets have higher BCs then most conventional weight 338 bullets but some 338 bullets offer much higher BC potential and some 30 cal bullets do as well.

Its a broad stroke to cover with one comment and to be honest impossible to do accurately.

Kirby Allen(50)
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

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Unread 05-22-2007, 10:55 AM
Bronze Member
Join Date: Oct 2006
Location: South Jordan, Utah
Posts: 73
Re: BC Question .30 vs. .33 cal

Thanks for the great replies, that explained alot to us.
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