Bullet Seating Depth Misconception
Bullet seating depth can make or break accuracy, but does it matter for velocity?
You know how certain cartridges are condemned because long, heavy bullets take up too much powder space? The 260 Remington, for example. It’s supposedly inferior to the 6.5 Creedmoor because those long, aerodynamically efficient 142- to 147-grain bullets must be crammed deep into the powder reservoir in order to fit many rifles’ short-action magazines.
Short and long 7mm bullets illustrate the myth that long bullets can't be effective if they infringe on powder space.
Beware long, heavy bullets! They protrude into powder space and render your cartridge useless. Or so goes the myth.
The Truth About 6.5 Creedmoor and 260 Rem. Powder Space
The 6.5 Creedmoor, on the other hand, is vastly better because it was designed with a longer neck and the shoulder pushed back 0.07” farther than the 260 Remington’s.
Don’t you see! If you seat the long bullet in the Creedmoor so that it fits the rifle’s magazine and/or just kisses the lands when chambered, its base won’t be protruding into the case’s powder space. So you can fill it with more powder. More powder means, duh, more muzzle velocity!
Image of 260 Rem. and 6.5 Creedmoor beside a long bullet that protrudes into both powder spaces puts the lie to one bullet seating depth argument.
Bullet seating depth is a big deal? Those long, sleek, high B.C.bullets are a perfect match for the 6.5 Creedmoor, but too much for the 260 Remington? This Berger 156-grain EOL illustrates how much that misconception is overstated. Of course this bullet is much better suited for larger 6.5 cases, but it clearly illustrates how seating depth can encroach on powder space.
Uh, ok. But… The 260 Remington drives these heavy bullets, on average, as fast as or slightly faster than does the 6.5 Creedmoor. There is no hard and fast standard here because every barrel and every factory load and every handloader’s custom load differs. Sometimes radically.
The Nosler Reloading Guide 8 lists water volume of cartridges with various bullets seated, and this is quite revealing. It shows the 6.5 Creedmoor with a 142-grain AccuBond Long Range seated to OverAllCartridgeLength of 2.805” with water volume of 46.8 grains. It shows the 260 Remington with the same bullet seated to OACL of 2.800” at water volume of 47.4 grains. Both are in 24” barrels. The top load for each shows the 260 Remington beating the Creedmoor by 99 fps MV.
Could Bias Be Biasing Bullet Seating Depth Concerns?
Of course, this could be biased data since Nosler’s competitor, Hornady, gave us the Creedmoor, even though they didn't name it the 6.5 Hornady. Interestingly, the Hornady Handbook of Cartridge Reloading 10th Edition shows the top 6.5 Creedmoor load besting the 260 Remington by 100 fps with its 143-grain ELD-X bullet. It does not list water capacity, but does show equal barrel length at 24 inches. And we must remember that different cases (brass) have different internal volumes depending on how thick each manufacturer makes its walls and bases/heads.
Image shows handloading manuals, all of which present slightly different data putting bullet seating depth "common knowledge" into question.
Handloading recipe books come up with different results for the same cartridges due to a host of performance altering conditions from barrel and chamber dimensions to internal volume of the brass used, to powder lot, humidity, atmospheric pressure and maybe moon phase.
(Just kidding on those last three.)
I find it interesting that not one powder is listed as common between the two despite their nearly identical powder volume and shape. It would seem fair to load both with the same powder to safe pressure levels to see which shot faster. The closest match in the Hornady recipe book may be Alliant 4350 in the 260 vs. Hodgdon 4350 in the Creedmoor. The 260 took 41.7 grains, the Creedmoor took 42 grains, resulting in a 50 fps MV advantage to the Creedmoor. Those volumes were with bullets seated.
Still a "Lot" to Consider
While this might seem to settle the argument, one must consider the variations in powder lots. Over the years thousands of handloaders have learned that a change in manufacturing lots can increase or decrease MV of their pet loads by 50 to 100 fps. There are also the differences in chambers and bores. A tighter chamber or bore can increase pressures and MV.
Compared side-by-side, the 260 Rem. (L) and 6.5 Creedmoor don't look radically different, and their performances prove it. Sierra load on right, SIG on left.
Regardless, 50 fps variation falls within the spread of most factory loads and many handloads from shot to shot with the exact same components. So… the main concern here should be effective muzzle velocity, the MV you desire (if not require) for your hunting. Does seating long bullets deep into powder space compromise MV to such a degree as to make one cartridge unsuitable for, say, elk hunting?
I don’t think so, and I’ll try to prove it next.
7mm-08 Remington Data Weakens Bullet Seating Depth Misconception
Now that we’ve established that the 260 Remington runs neck and neck with the supposedly better designed, more efficient 6.5 Creedmoor, lets drift on over to another cartridge, the 7mm-08 Remington. This one is often celebrated as a light recoiling launchpad for 140-grain bullets, maybe 150-grain, but any longer than that and you’re wasting your time. The stubby 7mm-08 just hasn’t the powder capacity to propel 175-grain bullets adequately, in part because they protrude so far into powder space.
Oh really?
Image shows various lengths of bullet beside a 7mm-08 cartridge to illustrate how deeply into its powder space they would intrude.
The Federal factory-loaded 7mm-08 cartridge with a 140-grain bullet aboard is at the established OACL. The other bullets are positioned to the same OACL so we can see how much of them would encroach on powder space. Clearly all of them do! From the
on left to the 168-grain Nosler ABLR on right. But they would do the same atop a 7x57 Mauser, 7mm Rem. Mag., or any other 7mm cartridge IF the rifle magazine didn't allow for seating bullets much farther out than standard OACL. Rather than worry about lost powder space, pay attention to the MV of your loads. Giving up 100 fps or even 200 fps hardly means your bullets are going to fall harmlessly to the ground.
One of the 7mm-08’s claims is that it’s a modern version of the famous 7x57mm Mauser, the 1892 cartridge that inspired the U.S. to “invent” the 30-06. The 7x57 was also the monstrous round Karamojo Bell famously hired to lay low some 800 elephants. (The other 200 or so he collected fell to a mix of other cartridges including a little 6.5mm Mannlicher.) Bell’s 7x57 was a Rigby rifle with the British designation 275 Rigby, identical to the German 7x57 Mauser. He shot German military ammo with 173-grain Round Nose bullets at about 2,300 fps and averaged about 1.5 cartridges per collected elephant. Most, if not all, of these were brain shots, but Bell also used the 7x57 on buffalo, as he relates here:
Karamojo Bell's 7x57 Testimonial
“I often had the opportunity of testing this extraordinary little weapon on other animals than elephant. Once, to relate one of the less bloody of its killings, I met at close range, in high grass, three bull buffalo. Having at the moment a large native following more or less on the verge of starvation, as the country was rather gameless, I had no hesitation about getting all three. One stood with head up about 10 yds. away and facing me, while the others appeared as rustles in the grass behind him. Instantly ready as I always was, carrying my own rifle, I placed a .276 solid in his chest. He fell away in a forward lurch, disclosing another immediately behind him and in a similar posture. He also received a .276, falling on his nose and knees. The third now became visible through the commotion, affording a chance at his neck as he barged across my front. A bullet between neck and shoulder laid him flat. All three died without further trouble, and the whole affair lasted perhaps four or five seconds.”
Photo shows a Cape buffalo, a large animal famous for taking a punch, yet Bell dropped three with three shots from his little 275 Rigby despite bullet seating depth that protruded into powder space.
If Bell was able to drop three Cape buffalo with three 173-grain 7x57 bullets at 2,300 fps, there's hope for all of us.
This establishes the 173-grain bullet at 2,300 fps adequate for toppling not just elephants, but the infamously durable Cape buffalo. Now let’s see what the even shorter 7mm-08 Remington can do. According, once again, to that Nosler reloading guide, nine different powders can push a 175-grain Accubond Long Range (B.C. .648) 2,472 to 2,623 fps. The long-action 280 Remington, often touted as a better option for long, heavy bullets, bests these speeds by 150 fps. The 308 Winchester, celebrated by legions as the ultimate, do-it-all 30-caliber, pushed a 175-grain bullet 2,617 fps, a smidgeon slower than the 7mm-08 Remington. You know as well as I that no elk, moose, nor big black bear is going to notice the difference.
Don't Worry. Be Happy
Now, there are arcane concerns among competitive shooters about such things as brass build up in the neck/shoulder junction, etc. but these are loading issues, not ballistic performance issues. The bottom line for hunting, as I see it, is STOP WORRYING ABOUT BULLETS INTERFERING WITH POWDER SPACE! Even if you can’t realize that extra 50 to 100 fps you might salvage with a different case design or longer magazine box, you can hunt and drop your game just fine. Memorize your trajectory table, shoot within your dead-certain targeting range, and leave the powder space worrying to the armchair theorists.
After five decades of hunting, shooting, and handloading, the author finds himself less and less interested in bullet seating depth to gain an additional 100 fps and more interested in figuring out how to stalk within 100 yards of an elk.
