As far as efficiency goes, the 366 DGW appears to do very well in that department. I too like to play around a bit with with cartridges that use mass quanities of powder. These are not as efficient but do have good ballistics.

30-378 WBY IMP
180gr Barnes X @3400 MV

100yds +2.3
200yds +2.6
300yds -.9
400yds -8.8
500yds -21.9
Does is shoot flat?


378 WBY
300 gr Barnes X @3000MV 5997 ft lbs

100yds +2.3 5330 ft lbs
200yds +1.8 4726 ft lbs
300yds -3.7 4176 ft lbs
400yds -15.1 3679 ft lbs
500yds -32.5 3229 ft lbs

416 WBY
400 gr Barnes X @ 2730MV 6477 ft lbs


100yds +2.3 5848 ft lbs
200yds +.6 5147 ft lbs
300yds -6.9 4515 ft lbs
400yds -21.4 3943 ft lbs
500yds -43.8 3431 ft lbs


All these numbers are moot if you cant hit where you are aiming. These big guns are not that easy to shoot accurately, especially in field situations. I would' nt hesitate on 300 yard shots with the last 2 alot further with the 30 cal. I think you' ll have to look hard to beat that 378WBY with a 300gr. Heck, out to 300 yards the 416 has good numbers, it will leave a bigger hole and penetrate very well, bullet drop is insignificant.
The .375 Barnes X has a BC of .555 and an SD of .305.
The .416 Barnes X has a BC of .546 and an SD of .330
The .308 Barnes X has a BC of .511

If I didnt already have the bases covered this 366 DGW shows merit.

yours in sport....AA