Tag Archives: VLD

RELOADERS CORNER: Why Not Flat-Base?

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A better question, given that the vast majority of popular rifle bullets are boat-tail, is why flat-base? KEEP READING

flat base bullet

Glen Zediker

Good question! I have something that at least has elements of an answer.

A boat-tail bullet is the standard for the majority of rifle bullets, and the domineering choice of long-range shooters. Competitive Benchrest shooters favor flat-base bullets. Flat-base is also popular with varmint-hunters: the stellar Hornady V-Max line for good instance.

Hmm.

We all want best accuracy, so why the difference? Consider the overriding characteristic of a flat-base bullet: it’s shorter. Now, since not all flat-base bullets are shorter overall than a same-weight boat-tail (they’re usually not), I seriously need to clarify that!

Clarification: a flat-base can be shorter, and lighter, than it would be if the same ogive or nosecone profile used then added a boat-tail. More: if they’re both the same weight and at least similar in profiles, a flat-base often has a longer bearing area than a boat-tail bullet, again because the boat-tail is sticking down there, or not. These are both a bonus to Benchrest or any other shorter-distance circumstance where utmost precision is the goal. (When I refer to capital-b “Benchrest,” I’m not talking about a shooting rest, but a competitive sport.) Shorter bullets allow slower barrel twists (bullet length, not weight, chiefly governs needed twist). Slower twists offer a miniscule improvement in damping a bullet’s orbital pattern in flight, and considering the likewise near-caliber-size 5-shot groups these folks are after, that matters. Bullets fly in a spiral, like a well-thrown football. Again comparing those with similar profiles, flat-base bullets stabilize faster and sooner than boat-tails, it’s a smaller spiral. Bullets with longer bearing areas tend to shoot better “easier,” less finicky. And, flat-base bullets can provide more cartridge case capacity.

vld and ld compare
Here’s unique. Jimmy Knox of the original JLK Bullets once made flat-base versions of his Davis-designed VLD (very low drag) boat-tails. So this is a .224-caliber flat-base 65gr LD (low drag), which is the same as his 80gr VLD shown with it, just no boat-tail. Why? It was more of a “Why not?” Idea was to provide better downrange performance for those with slower-twist-rate barrels, and to retain the flight pattern and in-barrel characteristics he liked about flat-base (and way on more speed). This idea was popular among some better High Power shooters about 15 years ago.

All those good points make it sound like flat-base provide superior accuracy. They might. By my experience, they do, but! Distance defines the limit of that truth.

The boat-tail provides an aerodynamic advantage, and the farther it flies, the greater this advantage. There are well-founded beliefs that boat-tails are less influenced by gas pressure thrusting against the bullet base. A good and most knowledgeable friend at Sierra told me that a boat-tail has an effectively more concentric radius at the base due to the junction point created by the angle on the tail and the bearing surface. Further, a flat-base, is, in effect, harder to make so that the base will have a radius that’s as concentric with the bullet bearing surface. Manufacture care and quality (related), of course, makes that more or less true or false. If the idea is that a good boat-tail is “easier” to make, that this shape makes the end product more forgiving of manufacturing errors, then I’ll accept that since it’s pretty hard to argue against, but, again, I really don’t think that boat-tail designs simply take up slack in quality tolerances. I’m sho no rocket-surgeon but I know that the tail slips the air better.

LD_ and Hornady 68
Same LD bullet compared to a Hornady 68gr HPBT. The 65 is a tic shorter overall but, because it’s a 15-caliber (!) ogive, way less bearing area (exception to the “rule” big-time) than the boat-tail next to it. The 65 had a higher BC but was über-tricky to get to shoot well. I could get these to just over 3000 fps in a 20-inch .223 Rem. Mostly because of the tiny bearing area.

This can get pounded completely into the ground because adding a boat-tail (and I’ll show a great example of just that) to a similar nosecone also adds weight to the bullet, and that increases BC. It’s not exactly a chicken-egg question, though, because the tail helps otherwise.

barts bullet
Here’s a 52gr boat-tail from Hornady (right) next to a 52gr custom Benchrest bullet. I said the overriding difference is that a flat-base bullet is shorter, but that’s not referring to overall length. A flat-base is shorter than it would be as a boat-tail, if the other dimensions were the same, and usually has a longer bearing area.

You might have also heard said that boat-tails shorten barrel life because the angled base directs burning propellant gases more strongly at the barrel surface. They do, and many steadfastly uphold that as a reason against them. More in a bit. However! Beyond 300 yards, at the nearest, there are no disadvantages in using boat-tail bullets that come close to surpassing their advantages.

There’s another debated advantage of a flat-base and that is they tend to shoot a little better in a barrel that’s about to go “out.” I’m talking about a good barrel that’s pushed the limit of its throat. That one is true too!

And speaking of barrel life, another is that flat-base bullets produce less flame-cutting effect than boat-tails. A barrel lasts longer if fed flat-base. True! Flat-base bullets “obturate” more quickly. Obturate means to “block,” but here it means to close a hole, which is a barrel bore, which means to seal it. The angled boat-tail creates a sort of “nozzle” effect. Can’t much be done about that, though, because when we need boat-tails we need them. That is, however, a big score of help for the varmint hunter.

There is a relatively obscure “combo” out there called a “rebated” boat-tail. This has a 90-degree step in from the bullet shank (body) to the tail. It steps in before the boat-tail taper is formed (they look like a flat-base with a boat-tail from a bullet a couple of calibers smaller stuck on there). It’s common for competitive .308 NRA High Power Rifle shooters, for instance, to switch from the popular Sierra 190gr MatchKing to a Lapua 185 rebated boat-tail when accuracy starts to fall off due to throat wear. Sure enough, the Lapua brings it back for a couple hundred more rounds.

rebated boat tail
Here’s a rebated boat-tail. 115 grain 6mm from David Tubb.

If anybody with heavy equipment making bullets for sale out there is listening: I’d like to see some more rebated boat-tail designs! It is, though, a challenge to make precisely.

So. What? So what? Well, if you are big into small groups, I very encourage some experimentation with flat-base bullets. Again, distance is the only limit to their potential goodness. 100 yards, yes. 200 yards, yes. 300 yards, no!

vld chamfer
One thing is for certain: Flat-base bullets are not nearly as easily seated! Some have an edge-radius, some don’t, but, they are very easy get started crooked, or difficult to get started straight, same effect. I strongly recommend taking steps to square case mouths and use a generous chamfer.

This article is adapted from Glen’s books, Handloading For Competition and Top-Grade Ammo, available at Midsouth HERE. For more information about other books by Glen, visit ZedikerPublishing.com