JBM yields some interesting info:
Allowing for a 7" vital zone and zeroing for Max Point Blank (about 300yds +/-), the big 7mm's look pretty good both near and far.
400yd performance of 300Wby with 155 Scenar at 3,450FPS.
Drop = 6.9"
Wind = 8.9" at 10mph
Vel = 2,630FPS
400yd peformance of a 7mm with 162 Amax at a "lowly" 3,200FPS.
Drop = 8.7"
Wind = 7.5" at 10mph
Vel = 2,590FPS
At this range, the 7mm will drop about 1.8" more but drift about 1.4" less. Impact speeds are nearly the same with the Scenar being 7 grains lighter and starting out a full 250FPS faster. It looks like the .30 cal doen't hold onto its velocity edge for too long, which is interesting considering that few folks shoot game animals out past 400yds. If they do, the comparison gets way uglier. I knew that speed is fleeting but BC is forever, still I didn't realize it would matter as much in instances inside "normal" ranges. That 162 is something....
Jpro: That has always been the attraction of 7mm's....that 162 is the ballistic equivilent of a 30 cal weighing (what?)...200+ grains?,which is really the right comparison.And how much powder do you have to burn in a mag 30 to get that heavy 30 cal bullet to 3200 fps?
Answer.....a lot;along with the recoil.
If you want to go "light" with the 7mm I know the Dakota (Mashburn, 300 WM case,etc)will likely start 120TTSX at over 3500;just a junior version of that 300 Weatherby load you cite.
Actually a garden variety 7RM will start a 140 BT or AB at 3250,and with the 300 yard sighting you list above,will only be down 8-9 " at 400,and about 26" at 500.If you are going to shoot light bullets, I would not bother with a necked down 300 Mag,or Mashburn, etc.It is just not worth the effort and expense of a wildcat.
The Nosler manual shows loads for the 7mmRM of 3300 with a 140, so a 300WM necked down is not worth it;neither is the Mashburn. The real advantage of the larger cases is with the higher veocity of the heavier 7mm bullets.
The figures look correct based on 300 yard zero....even a crummy 160 gr Nosler Partition started at 3200 will only be down about 9" at 400 from a 300 yard zero.
For chuckles, run a 175 Partition (BC 519) at 3100 or so, against a 300 Weatherby with 180's at 3200.It hangs pretty close....and it takes a lot less powder in the 7mm(about 73 gr in my rifle),to get the 175 to speed.
Despite the din over real LR shooting, I have never had to go beyond 400 for my BIGGEST bucks;most were half that distance or under.
