boattail and flatbase bullets 111412

Flat Base Or Boattail?

As hunters, we put a lot of thought into the tips of our bullets.  Roundnoses, spire points, plastic tips and such are all worried over to ensure that the bullet we’re using is right for the game we’re hunting.  But have you ever given as much consideration to the other end of your bullet–the base?

boattail and flatbase bullets 111412
Should you use a flat base or boattail bullet for your type of hunting? Does it even matter anymore?

In the scheme of things, the base of your bullet probably isn’t going to make any more of a difference between a hit or a miss, a clean kill or a wound, than the bullet tip, but it is something to consider if you’re on a once-in–a-lifetime hunt and want to eliminate as many variables as possible that could leave you standing there wondering what went wrong if a trophy animal bounds away seemingly unscathed.

jacket/core separation 111412
This boattail bullet was fired into a whitetail deer from about 20 yards. The core completely separated from the jacket, and the penetration was poor.

There are generally two types of bases on hunting bullets—flat base and boattail—and the practical differences between them may not be what you think. Both have their benefits, and their drawbacks. For example, when it comes to pure accuracy, flat base bullets are inherently more accurate than boattails, and that’s why you see the “short range” Benchrest shooters using them. The reason is because it’s easier to make their bases perfectly square

with the sides of the bullets than it is to make boattails perfectly concentric and on straight.

Another benefit of flat base bullets is that for a given caliber and bullet weight, they’re shorter overall, so are more easily stabilized in a slower rifling twist. That shorter length, however, puts their center of gravity more toward the rear of the bullet, and that tends to offset stability gained from the shorter length.

roundnose mushroom 111412
This is a 180-grain roundnose fired from a .35 Remington. It mushroomed well and retained most of its weight–a good choice for close shots on medium game.

Finally, flat base bullets generally experience less jacket/core separation on impact. If you think of the bullet jacket like an ice cube tray and the lead core as the ice, it should be obvious that the right angle inside of a flat base jacket holds onto the core better than the tapered inside of a boattail jacket. On big game, you want a bullet that penetrates, and that means using a bullet that stays together and retains its weight instead of coming completely apart during expansion.

I’m not suggesting standard cup-and-core boattails are the wrong bullet to use for hunting—they have their place and their advantages—such as at very long range on light-bodied game. Boattails increase the ballistic coefficient of bullets, which helps them overcome air resistance and wind deflection. The difference in the amount of bullet drop between flat base and boattail bullets won’t amount to much until well past the range at which most of us shoot, but the boattail’s better ballistic coefficient makes errors in wind deflection correction and range estimation more forgiving. Whatever loss of accuracy there is from the boattail’s inherent manufacturing flaws are more than offset by their ability to overcome adverse or unknown shooting conditions. And if you’re a handloader, boattail bullets are simply easier to start into a case mouth and seat with less chance of crumpling or bulging a case neck.

Nosler Partition base 111412
This is the base of a Nosler Partition bullet. It shows that on impact, a bullet’s core tends to shift forward in the jacket. In this design, though, the partition retains the base core.

Thankfully, bullet technology is at a point where we really don’t have to choose between a flat base and a boattail for good terminal performance. There are plenty of bullets that give you the benefits of both without some of their drawbacks.

From a design standpoint, Nosler has its Solid Base boattails that retain their cores during penetration better than standard cup-and-core boattails. With the Solid Base design, the entire boattail base is solid copper, so instead of being tapered inside the base, the lead core bottoms out against an all-flat surface.  It’s like Nosler made a flat base inside a boattail so there’s less a chance of the core popping out as it impacts and passes through game. That design also shifts the bullet’s center of gravity forward helping with stability.

Nosler Solid Base Bullet 111412
Nosler’s Solid Base bullet has a solid copper boattail base and the lead core bottoms out against a flat surface like on a flat base bullet.

There are also bullets that mechanically retain the core such as Hornady’s InterLock boattail bullets. An InterLock is essentially a raised edge inside the bullet jacket that grips the core solidly when it’s swaged into place during bullet forming. I’ve shot a lot of big game with Hornady InterLock bullets and I can’t recall an instance of jacket/core separation.

Another technique to help boattail bullets perform better is by bonding the jacket and the core.  Often, this bond is so strong that it’s not uncommon to recover expanded bullets with significant amounts of lead still bonded to the petals instead of being ripped or wiped off. Swift Bullets uses bonding in its Scirocco II line, and if you section one you’ll also see that the lead core sits in a flat-bottom cavity much like Nosler’s Solid Base bullets.

Bullet jaket and core 111412
If you think of the jacket like an ice cube tray and the core as the ice, it’s easy to see how boattail cores separate more easily unless locked or bonded into place.

Of course, we can’t forget all-copper bullets such as Barnes. They offer the sleek design and high ballistic coefficient of boattail bullets, and expand reliably without any lead core at all.

There are continuing efforts being made in the Benchrest shooting community to make boattail bullets that behave like flat bases at all ranges,

and flat base bullets that behave like boattails at long range. Those efforts include rebated boattail designs that have an abruptly reduced bullet diameter before the boattail is formed, and FBVLD, or flat based very low drag bullets that have an extremely long nose, or ogive (pronounced o-jive), for minimum nose drag to compensate for the greater base drag. I also understand Berger Bullets has been working on a method of forming boattails so that they are more concentric. If those efforts prove successful, it’s likely that we’ll see them adapted to hunting bullets in some fashion. Until then, if using standard cup-and-core bullets, you’re probably better off with flat base bullets on heavy game at close to long range, and boattail bullets on light game at very long range.—Scott Mayer

 

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6 thoughts on “Flat Base Or Boattail?”

  1. Great article. Design info is correct. Most folks didn’t know those facts. Try to shoot the most accurate bullet for your gun.

  2. Scott, I have harvested Antelope, Black bear, Deer and Elk all over 500 yards. My rifle is a custom built 7mm RUM. The barrel is a Lilja SS 14 to 1 twist 27.5 inches long. It was built specifically for long range, if needed, shots. I shoot Berger Y140 grain VLD hunting bullets. The weight retention has been 90%+ on all the animals mentioned. I find your article flat base vs boattail is a bit perplexing. What do you consider a heavy skinned animal. My black bear ranged 763 yards.

    Keith Zimmerman

  3. Keith, Thanks for taking the time to read my article and for sharing your experiences. I consider a boattail the right choice if you’re regularly taking 500-yard+ shots as the design is more forgiving for any errors in range estimation or wind deflection.
    I don’t know your starting velocity, but I’m going to estimate it at about 3,150 fps. A quick ballistics check using a G1 BC estimates 500 yard velocity with the 140-grain Berger VLD hunting bullet as approximately 2250 fps. That impact velocity is low enough that I would expect the high weight retention you’re experiencing.
    I think what you might be finding perplexing are my last couple of sentences, and I can see where that can happen. I’ll try to clarify, and please keep in mind it’s a recommendation based on the inherent strengths and weaknesses of the two designs, not “set-in-stone” terminal ballistic rules. If using standard cup-and-core bullets, the flatbase bullet is the better choice at close range and higher impact velocities, especially on larger game, as their construction tends to make them hold together better at high impact velocity than standard cup-and-core boattails. At longer ranges, the boattail gets the nod because of its improved accuracy potential in field conditions.

  4. I have a friend that expresses that the reason a flat base is more accurate than a boat tail is because the flat surface at the back of the bullet allows the gas to escape around the bullet uniformly and that it doesn’t escape the same around a boat tail I find this theory to be flawed but won’t contest it what is your theory on this

  5. It’s interesting how you said that ammo with a flat base holds a core better than some other kinds of ammo. This would be good if you wanted to try to have someone recast your ammo for you after you have fired it. That way you could save some money without having to worry about having to put any effort in yourself.

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