300 Win Mag Races 7mm Rem Again!

A reader recently requested a ballistic comparison between same weight bullets in a 300 Win. Mag. and 7mm Rem. Mag. launched at maximum velocities for each. (See previous 300 WM vs. 7mm RM comparisons on this site here and here. These demonstrate there's more than one way to run a race.) Now, here’s the reader's request:

Ron:

7mm Rem Mag vs. 300 Win Mag

1)) Load each of them with the very ‘maximum’ amount of powder each case will safely hold, and also with exact same type of powder.

2)) Load both of them with exact same bullet grain weight(150, 165, or 180 grain, etc.) an example is both of them with a 150 grain bullet, and also same bullet type.

Then I ‘do’ know the 300 Win Mag will have more velocity, being more FeetPerSecond than the 7 mm Rem Mag.

But I would also like to know, in the scenario I mentioned above, please also compare which cartridge will have the ‘best’ Ballistic Coefficient, Energy ft/lbs, flatter shooting, etc.??

This is a fair comparison that I would like to see done. Thank you.

David

David, one can't expect the same powders in different cartridges to produce maximum velocities in each, so I went with those that would produce maximum velocities at safe pressure levels and ran the test using G1 BC numbers (which won’t beas accurate at G7 numbers, but those are still too unfamiliar to most shooters.) Here are the resulting ballistic charts comparing two nearly identical-weight Hornady ELD-X bullets, some of the most ballistically efficient on the market:

This image shows the ballistic performance of a 7mm Rem. Mag. shooting a 175-gr. bullet, BC .675

And we have a winner. The 300 Win. Sort of. Maybe. Truth be told, it's a mixed bag with each "winning" in different categories. But questions arise. If both these cartridges are made from the 375 H&H Magnum brass (belted case with .532” head diameter,) and both fit standard (30-06-length) actions, why does the 300 WM generate 200 fps more velocity? Basic answer: It has water capacity of 82.3 grains with this bullet aboard. The 7mm Rem. Mag. has a water capacity of 77 grains with its bullet. This results in the 300 accommodating 78.9 grains of Alliant RL-25 powder and the 7mm squeezing in just 66.2 of the same powder for safe pressure levels according to Hornady’s Handbook of Cartridge Reloading, Tenth Edition. For the velocity recorded above, however, Alliant RL-26 was used in the 300 WM. 

Okay. So on to the next question: Why does the 300 have more volume? Because its overall case length is 2.620”. The 7mm RM case has an OAL of just 2.5”. More significantly, the 300 Win case shoulder sits at 2.356” while the 7mm’s is back at 2.040". That accounts for most of the capacity difference, despite the typical complaint of 300 WM bullets intruding into powder space.

This image shows dimension of the 300 Win Mag cartridge.

Illustrations taken from Hornady Manual, 10th Edition. Note shorter neck of the 300 Win. 

Some handloaders say the shorter base-to-shoulder dimension of the 7mm is good because it allows the 7mm to have a longer neck for grabbing more of the bullet, which is supposed to be better for accuracy. Indeed, the 300 Win. Mag. is often criticized for its “too short” neck, which is less than the .308” diameter of the bullets it shoots. Yet, somehow, the 300 Win. Mag. has managed to win many 1,000-yard competitions and has been widely used as a U.S. military sniper round. Not bad for an inaccurate cartridge. My current 7mm Rem. Mag., a Jim Borden Timberline custom, groups sub-MOA, too. So much for inaccuracy issues. 

What all of this means to the average hunter is -- not much. Few of us engage game beyond 400 yards and fewer of us ever should. Our rifles, cartridges and bullets may be capable of 1,000-yard performance. We rarely are. When selecting suitable hunting or even target/fun rounds, we should pay as much attention to ballistics, recoil, etc. as we can and/or want to. Minimal drop and drift compensate for our mistakes and make it easier to hit. But when the butt stock hits the shoulder, it’s more about our abilities to aim and fire accurately than our bullets' abilities to fly. Some rifles, cartridges, scopes and bullets make this easier than others. Those are the ones we should use. Several newer cartridges in .308 and .284 (7mm) outperform the old 300 Win and 7mm Rem. But not by much. 

Image shows the longer 300 Win Mag cartridge beside the shorter 7mm Rem Mag.

Ron Spomer has worked extensively with the 7mm Rem. Mag. and 300 Win. Mag. and many other cartridges at home and around the world. He's convinced that most debates about their relative merits are much ado about little. The game he's take with them have tended to agree. Nevertheless, Ron still enjoys arguing ballistics. Pull up a chair.