Flat Base vs. Boat Tail - 223 Rem

[Nick_C_S]

I recently started loading for 223 Rem for my AR-15's.

The two bullets I'm focused on right now are the Winchester 64gn PP - a Flat Based bullet; and the Sierra 65gn SBT - a Boat Tail.

My question is: What's the difference?

I mean, visually, it's obvious. And from what I understand, the Boat Tail design is to reduce air drag; and thus, potentially sail farther and straighter. That said, why have a flat base? There must be some "trade off" between the two.

Boat Tails are ballistically superior (I guess) and are easier to load (get started into the case mouth); so why have Flat Based bullets at all?

What am I missing? <-- I guess that's the real question

[MarkCO]

While you might not be able to see the difference in many AR15s, flat based bullets that are on the lighter (<55 grains) side "might" be a little more accurate out to about 200 yards than the same weight boat tail bullets. In my match grade AR15s, the 50 grain NBT still has the best accuracy 200 yards and in, typically around .2MOA if the wind behaves. That beats about 35 other bullets I have tried over the years.

When you get past 55 grains, there really is not a generality that can be made as other factors have much more significance. I have never been able to shooter a better group with a flat based bullet than a boat-tail in .223 past 300 yards. In .308, there are some excellent FB bullets, but in most other calibers, true match grade FB bullets that are heavy for caliber are pretty rare.

I would bet on the Sierra, but not because it has a boat tail.

[T. O'Heir]

BT's tend to be better for long range. Flat bottoms are better at close range. Has to do with stabilizing. Rumour has it that flat base bullets release from the muzzle cleaner. Berger says they're easier to make consistent because flat is always flat. No varmint will care one way or the other.
"...are easier to load..." That's what the case mouth chamfer is for. Takes the place of the flaring done to a handgun case.

[Stats Shooter]

Just like everyone else said, flat base bullets tend to be a bit more consistent at lower costs, and a bit more accurate at short range as the stabilize faster.

But flat base bullets can be shot long range and boat tail bullets at short range too.

However, a lot of this stuff is Academic unless you are at a point where very subtle differences matter.

[Unclenick]

Flat base bullets are shorter for the same weight than a boattail, so they may be stabilized with a slightly slower twist. This is why short range benchrest competitors often use fairly stubby flat base bullets. The shorter twist produces less dispersion due to any ting bullet imbalance or CG offset due to imperfectly straight seating and cartridge concentricity. Short range benchrest doesn't have to worry about wind so much, or they'd use boattails, too.

The other factor is simply that it's easier to make dies that produce a square base than it is to produce dies that cause the boattail to be perfectly centered in the bullet. This is often seen on cheap bullets where the boattail meets the bearing surface unevenly all the way around. So when that cheap bullet starts to clear the muzzle, the muzzle blast playing off of it creates more deflecting force on one side, imparting to the bullet a slow but real drift of the intended trajectory path that results in it opening the group up.

Finally, though a small difference, the boattail takes longer to clear the muzzle than a square base does. This gives muzzle blast more time to play off the bullet base and try to tip it or deflect it and garner the influence of any imperfection in the bullet or muzzle crown asymmetry.

That said, because the boattail reduces drag, a bullet equipped with one loses velocity more slowly than a flat base does and is therefore deflected less by the wind. So if you have enough twist for the longer BT and you have bullets that are perfectly formed by a high grade match bullet maker, you may see no practical drawback to using them in your gun.

[Nick_C_S]

Thanks for the replies folks. Good information. I learned a few things.

I kind of figured out for myself that BT's, being slightly longer per weight, would be slightly more difficult to stabilize - all else being equal. My guns' barrels are 1:7 twist; so stabilization is not really an issue in my application.

What I didn't factor is the potential deflection from muzzle blast because BT's don't leave the barrel as "cleanly" as a flat base. Interesting concept. I'm using Sierra's #1395 65gn SBT's. I'm assuming that Sierra is a top quality bullet and their BT's are pretty symmetrical all the way around the base.

I should also mention that I only plan on shooting at targets from 50 to 100 yards. Groups of 2" to 3" would be acceptable. I'm not asking a lot from either bullet I'm using.

So if you have enough twist for the longer BT and you have bullets that are perfectly formed by a high grade match bullet maker, you may see no practical drawback to using them in your gun.

Yeah, that's kind of where I am. ^^

Boat tails are a lot easier to load; specifically, to get started. Without flaring, I struggle starting a flat based bullet. Chamfering with a VLD tool helps, but it's still a bit of a hastle that simply doesn't exist with BT bullets. I think for me, sticking with Sierra's 65gn SBT's are the way to go.

[Longshot4]

Even though the quicker stabilizing is better for accuracy. It's a tough job to shoot in the wind for the light weight bullets.

Would you agree?

[Unclenick]

That's generally true. The bottom line, though, is ballistic coefficient. Whether lighter or heavier, the bullet with the lower BC is the one the wind will deflect least during any matching time of flight. The feeling that the lighter bullets don't do as well comes from the fact their BC's are generally not up to that of heavier bullets.

[Jeffm004]

I am behind you with 5.56. I was surprised at the variation with factory, this was at 100. I went back to the PPU Match in the middle after the Norma. I have a lifetime of brass I plan to sort by weight eventually. For now I ordered some prepped Lake City brass from Wes Sage (one sale $25/250). That will be my base line for weight variation and performance. I have a .270 with a demonstrable preference for flat base, so I'll be trying both. My goal is minute of prairie dog for 200.

[g.willikers]

A lot of this stuff is Academic unless you are at a point where very subtle differences matter.

Makes sense for many reloading and ammo questions that are routinely asked on this and most other forums.
I've never gotten anywhere near that point myself, although it can be an interesting endeavor to pursue for some.

[rg1]

Win 64 PP bullets I've loaded vary in weight a bit more than some other bullets. I weigh and sort them in 2 groups, lighter and heavier. Mine are from years ago when the 64 PP was first introduced so yours may be more consistent? My accuracy improved slightly weighing and sorting them. Out to 300 yards the difference between fb and bt would be hard to distinguish the difference in trajectory. Flat bases may even be more accurate. Good hunting bullet the 64 PP.