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)
